Download 1 - JAVA PLATFORM, ENTERPRISE EDITION

1 - java platform, enterprise edition
1 - JAVA PLATFORM, ENTERPRISE
EDITION
1.1 the state of java EE
The Java EE 6 is the current Java Enterprise Edition specification (as of Oct. 2011). Compared
to the previous specification, it introduces several new features:
•
Profiles, configurations of the Java EE platform targeted at specific classes of
applications. Specifically, the Java EE 6 platform introduces a Web Profile targeted at
web applications, as well as a Full Profile that contains all Java EE technologies.
•
New technologies, including the following:
•
Java API for RESTful Web Services (JAX-RS)
•
Contexts and Dependency Injection for the Java EE Platform (JSR-299),
informally known as Web Beans
•
Dependency injection for Java (JSR 303)
•
Bean Validation (JSR 303)
•
Java Authentication Service Provider Interface for Containers (JASPIC)
•
New features for Enterprise JavaBeansTM (EJBTM) components
•
New features for servlets
•
New features for JavaServer TM Faces components
1.2 the application model
The application model starts with the Java programming language and the Java Virtual
Machine. This combination provides high portability, scalability and developing efficiency.
Java EE is designed to support applications that implement enterprise services for customers,
employees, suppliers, partners, and others who make demands on or contributions to the
enterprise. Such applications are inherently complex, potentially accessing data from a variety of
sources and distributing applications to a variety of clients.
To better control and manage these applications, the business functions to support these
various users are conducted in the middle tier. The middle tier represents an environment that is
closely controlled by an enterprise's information technology department. The middle tier is
typically run on dedicated server hardware and has access to the full services of the enterprise.
The Java EE application model defines an architecture for implementing services as multi-tier
applications that deliver the scalability, accessibility, and manageability needed by enterpriselevel applications. This model partitions the work needed to implement a multi-tier service into two
parts: the business and presentation logic to be implemented by the developer, and the standard
system services provided by the Java EE platform. The developer can rely on the platform to
provide solutions for the hard systems-level problems of developing a multi-tier service.
1
1 - java platform, enterprise edition
1.3 distributed multitiered applications
The Java EE platform uses a distributed multitiered application model for enterprise
applications. Application logic is divided into components according to function, and the various
application components that make up a Java EE application are installed on different machines
depending on the tier in the multitiered Java EE environment to which the application component
belongs. Figure 1.1 shows generic multitiered Java EE applications divided into the tiers
described in the list below. The Java EE application parts shown in figure 1.1 are presented in the
Java EE components section.
•
client-tier components run on the client machine.
•
web-tier components run on the Java EE server.
•
business-tier components run on the Java EE server.
•
enterprise information system (EIS)-tier software runs on the EIS server
Figure 1.1 Distributed multitiered applications
Although a Java EE application can consist of the three or four tiers shown in figure 1.1, Java
EE multitiered applications are generally considered to be three-tiered applications because they
are distributed over three locations: client machines, the Java EE server machine, and the
database or legacy machines at the back end. Three-tiered applications that run in this way
extend the standard two-tiered client and server model by placing a multithreaded application
server between the client application and back-end storage.
2
1 - java platform, enterprise edition
1.4 java EE components
Java EE applications are made up of components. A Java EE component is a self-contained
functional software unit that is assembled into a Java EE application with its related classes and
files and that communicates with other components.
The Java EE specification defines the following Java EE components:
•
Application clients and applets are components that run on the client.
•
Java Servlet, JavaServer Faces, and JavaServer Pages (JSP) technology components
are web components that run on the server.
•
Enterprise JavaBeansTM (EJB) components (enterprise beans) are business components
that run on the server.
Java EE components are written in the Java programming language and are compiled in the
same way as any program in the language. The difference between Java EE components and
“standard” Java classes is that Java EE components are assembled into a Java EE application,
are verified to be well formed and in compliance with the Java EE specification, and are deployed
to production, where they are run and managed by the Java EE server.
1.5 java EE Clients
A Java EE client can be a web client or an application client.
1.5.1 Web Clients
A web client consists of two parts: (1) dynamic web pages containing various types of markup
language (HTML, XML, and so on), which are generated by web components running in the web
tier, and (2) a web browser, which renders the pages received from the server.
A web client is sometimes called a thin client. Thin clients usually do not query databases,
execute complex business rules, or connect to legacy applications. When you use a thin client,
such heavyweight operations are off-loaded to enterprise beans executing on the Java EE server,
where they can leverage the security, speed, services, and reliability of Java EE server-side
technologies.
1.5.2 Applets
A web page received from the web tier can include an embedded applet. An applet is a small
client application written in the Java programming language that executes in the Java virtual
machine installed in the web browser. However, client systems will likely need the Java Plug-in
and possibly a security policy file in order for the applet to successfully execute in the web
browser.
Web components are the preferred API for creating a web client program because no plug-ins
or security policy files are needed on the client systems. Also, web components enable cleaner
and more modular application design because they provide a way to separate applications
programming from web page design. Personnel involved in web page design thus do not need to
understand Java programming language syntax to do their jobs.
3
1 - java platform, enterprise edition
1.5.3 Application Clients
An application client runs on a client machine and provides a way for users to handle tasks that
require a richer user interface than can be provided by a markup language. It typically has a
graphical user interface (GUI) created from the Swing or the Abstract Window Toolkit (AWT) API,
but a command-line interface is certainly possible.
Application clients directly access enterprise beans running in the business tier. However, if
application requirements warrant it, an application client can open an HTTP connection to
establish communication with a servlet running in the web tier. Application clients written in
languages other than Java can interact with Java EE 6 servers, enabling the Java EE 6 platform
to interoperate with legacy systems, clients, and non-Java languages.
1.5.4 The JavaBeans Component Architecture
The server and client tiers might also include components based on the JavaBeans component
architecture (JavaBeans components) to manage the data flow between an application client or
applet and components running on the Java EE server, or between server components and a
database. JavaBeans components are not considered Java EE components by the Java EE
specification.
JavaBeans components have properties and have get and set methods for accessing the
properties. JavaBeans components used in this way are typically simple in design and
implementation but should conform to the naming and design conventions outlined in the
JavaBeans component architecture.
1.5.5 Java EE Server Communications
Figure 1.2 shows the various elements that can make up the client tier. The client
communicates with the business tier running on the Java EE server either directly or, as in the
case of a client running in a browser, by going through JSP pages or servlets running in the web
tier. Your Java EE application uses a thin browser-based client or thick application client. In
deciding which one to use, you should be aware of the trade-offs between keeping functionality on
the client and close to the user (thick client) and off-loading as much functionality as possible to
the server (thin client). The more functionality you off-load to the server, the easier it is to
distribute, deploy, and manage the application; however, keeping more functionality on the client
can make for a better perceived user experience.
4
1 - java platform, enterprise edition
Figure 1.2 Server communication
1.6 web components
Java EE web components are either servlets or pages created using JSP technology (JSP
pages) and/or Java Server Faces technology. Servlets are Java programming language classes
that dynamically process requests and construct responses. JSP pages are text-based documents
that execute as servlets but allow a more natural approach to creating static content. Java Server
Faces technology builds on servlets and JSP technology and provides a user interface component
framework for web applications.
Static HTML pages and applets are bundled with web components during application assembly
but are not considered web components by the Java EE specification. Server-side utility classes
can also be bundled with web components and, like HTML pages, are not considered web
components.
The web tier, like the client tier, might include a JavaBeans component to manage the user
input and send that input to enterprise beans running in the business tier for processing.
1.7 business components
Business code, which is logic that solves or meets the needs of a particular business domain
such as banking, retail, or finance, is handled by enterprise beans running in the business tier.
Figure 1.3 shows how an enterprise bean receives data from client programs, processes it (if
necessary), and sends it to the enterprise information system tier for storage. An enterprise bean
also retrieves data from storage, processes it (if necessary), and sends it back to the client
program.
5
1 - java platform, enterprise edition
Figure 1.3 Web, Business and EIS Tiers
1.8 enterprise information system tier
The enterprise information system tier handles EIS software and includes enterprise
infrastructure systems such as enterprise resource planning (ERP), mainframe transaction
processing, database systems, and other legacy information systems. For example, Java EE
application components might need access to enterprise information systems for database
connectivity.
1.9 java EE Containers
Normally, thin-client multitiered applications are hard to write because they involve many lines
of intricate code to handle transaction and state management, multithreading, resource pooling,
and other complex low-level details. The component-based and platform-independent Java EE
architecture makes Java EE applications easy to write because business logic is organized into
reusable components. In addition, the Java EE server provides underlying services in the form of
a container for every component type. Because you do not have to develop these services
yourself, you are free to concentrate on solving the business problem at hand.
1.9.1 Container Services
Containers are the interface between a component and the low-level platform-specific
functionality that supports the component. Before a web, enterprise bean, or application client
component can be executed, it must be assembled into a Java EE module and deployed into its
container.
6
1 - java platform, enterprise edition
The assembly process involves specifying container settings for each component in the Java
EE application and for the Java EE application itself. Container settings customize the underlying
support provided by the Java EE server, including services such as security, transaction
management, Java Naming and Directory Interface (JNDI) lookups, and remote connectivity.
Here are some of the highlights:
•
The Java EE security model lets you configure a web component or enterprise bean so
that system resources are accessed only by authorized users.
•
The Java EE transaction model lets you specify relationships among methods that make
up a single transaction so that all methods in one transaction are treated as a single unit.
•
JNDI lookup services provide a unified interface to multiple naming and directory services
in the enterprise so that application components can access these services.
•
The Java EE remote connectivity model manages low-level communications between
clients and enterprise beans. After an enterprise bean is created, a client invokes methods
on it as if it were in the same virtual machine.
Because the Java EE architecture provides configurable services, application components
within the same Java EE application can behave differently based on where they are deployed.
For example, an enterprise bean can have security settings that allow it a certain level of access
to database data in one production environment and another level of database access in another
production environment.
The container also manages nonconfigurable services such as enterprise bean and servlet life
cycles, database connection resource pooling, data persistence, and access to the Java EE
platform APIs.
1.9.2 Container Types
The deployment process installs Java EE application components in the Java EE containers
illustrated in figure 1.4.
7
1 - java platform, enterprise edition
Figure 1.4 Java EE Server and Containers
•
Java EE server - the runtime portion of a Java EE product. A Java EE server provides
EJB and web containers.
•
Enterprise JavaBeans (EJB) container - manages the execution of enterprise beans for
Java EE applications. Enterprise beans and their container run on the Java EE server.
•
Web container - manages the execution of JSP page and servlet components for Java
EE applications. Web components and their container run on the Java EE server.
•
Application client container - manages the execution of application client components.
Application clients and their container run on the client.
•
Applet container - manages the execution of applets. Consists of a web browser and Java
Plug-in running on the client together.
1.10 support for web services
Web services are web-based enterprise applications that use open, XML-based standards and
transport protocols to exchange data with calling clients. The Java EE platform provides the XML
APIs and tools you need to quickly design, develop, test, and deploy web services and clients that
fully interoperate with other web services and clients running on Java-based or non-Java-based
platforms.
To write web services and clients with the Java EE XML APIs, all you do is pass parameter data
to the method calls and process the data returned; or for document-oriented web services, you
send documents containing the service data back and forth. No low-level programming is needed
because the XML API implementations do the work of translating the application data to and from
an XML-based data stream that is sent over the standardized XML-based transport protocols.
These XML-based standards and protocols are introduced in the following sections.
The translation of data to a standardized XML-based data stream is what makes web services
and clients written with the Java EE XML APIs fully interoperable. This does not necessarily mean
that the data being transported includes XML tags because the transported data can itself be plain
text, XML data, or any kind of binary data such as audio, video, maps, program files, computeraided design (CAD) documents and the like. The next section introduces XML and explains how
parties doing business can use XML tags and schemas to exchange data in a meaningful way.
1.10.1 XML
XML is a cross-platform, extensible, text-based standard for representing data. When XML data
is exchanged between parties, the parties are free to create their own tags to describe the data,
set up schemas to specify which tags can be used in a particular kind of XML document, and use
XML stylesheets to manage the display and handling of the data.
For example, a web service can use XML and a schema to produce price lists, and companies
that receive the price lists and schema can have their own stylesheets to handle the data in a way
that best suits their needs. Here are examples:
•
One company might put XML pricing information through a program to translate the XML
to HTML so that it can post the price lists to its intranet.
•
A partner company might put the XML pricing information through a tool to create a
marketing presentation.
•
Another company might read the XML pricing information into an application for
processing.
8
1 - java platform, enterprise edition
1.10.2 SOAP Transport Protocol
Client requests and web service responses are transmitted as Simple Object Access Protocol
(SOAP) messages over HTTP to enable a completely interoperable exchange between clients
and web services, all running on different platforms and at various locations on the Internet. HTTP
is a familiar request-and response standard for sending messages over the Internet, and SOAP is
an XML-based protocol that follows the HTTP request-and-response model.
The SOAP portion of a transported message handles the following:
•
Defines an XML-based envelope to describe what is in the message and how to process
the message
•
Includes XML-based encoding rules to express instances of application-defined data types
within the message
•
Defines an XML-based convention for representing the request to the remote service and
the resulting response
1.10.3 WSDL Standard Format
The Web Services Description Language (WSDL) is a standardized XML format for describing
network services. The description includes the name of the service, the location of the service,
and ways to communicate with the service. WSDL service descriptions can be stored in UDDI
registries or published on the web (or both). The Sun Java System Application Server Platform
Edition 8 provides a tool for generating the WSDL specification of a web service that uses remote
procedure calls to communicate with clients.
1.10.4 UDDI and ebXML Standard Formats
Other XML-based standards, such as Universal Description, Discovery and Integration (UDDI)
and ebXML, make it possible for businesses to publish information on the Internet about their
products and web services, where the information can be readily and globally accessed by clients
who want to do business.
1.11 java EE 6 core technologies and APIs
Figure 1.5 illustrates the availability of the Java EE 6 platform APIs in each Java EE container
type. The following sections give a brief summary of the technologies required by the Java EE
platform, and the APIs used in Java EE applications.
9
1 - java platform, enterprise edition
Figure 1.5 Java EE Platform APIs
1.11.1 Enterprise JavaBeans Technology
An Enterprise JavaBeans (EJB) component, or enterprise bean, is a body of code having fields
and methods to implement modules of business logic. You can think of an enterprise bean as a
building block that can be used alone or with other enterprise beans to execute business logic on
the Java EE server.
There are two kinds of enterprise beans: session beans and message-driven beans. A session
bean represents a transient conversation with a client. When the client finishes executing, the
session bean and its data are gone. A message-driven bean combines features of a session bean
and a message listener, allowing a business component to receive messages asynchronously.
Commonly, these are Java Message Service (JMS) messages.
In Java EE 5, entity beans have been replaced by Java persistence API entities. An entity
represents persistent data stored in one row of a database table. If the client terminates, or if the
server shuts down, the persistence manager ensures that the entity data is saved.
1.11.2 Java Servlet Technology
Java servlet technology lets you define HTTP-specific servlet classes. A servlet class extends
the capabilities of servers that host applications that are accessed by way of a request-response
programming model. Although servlets can respond to any type of request, they are commonly
used to extend the applications hosted by web servers.
1.11.3 JavaServer Pages Technology
JavaServer Pages (JSP) technology lets you put snippets of servlet code directly into a textbased document. A JSP page is a text-based document that contains two types of text: static data
(which can be expressed in any text-based format such as HTML, WML, and XML) and JSP
elements, which determine how the page constructs dynamic content.
1.11.4 JavaServer Pages Standard Tag Library
The JavaServer Pages Standard Tag Library (JSTL) encapsulates core functionality common to
many JSP applications. Instead of mixing tags from numerous vendors in your JSP applications,
you employ a single, standard set of tags. This standardization allows you to deploy your
applications on any JSP container that supports JSTL and makes it more likely that the
10
1 - java platform, enterprise edition
implementation of the tags is optimized.
JSTL has iterator and conditional tags for handling flow control, tags for manipulating XML
documents, internationalization tags, tags for accessing databases using SQL, and commonly
used functions.
1.11.5 JavaServer Faces
JavaServer Faces technology is a user interface framework for building web applications. The
main components of JavaServer Faces technology are as follows:
•
A GUI component framework.
•
A flexible model for rendering components in different kinds of HTML or different markup
languages and technologies. A Renderer object generates the markup to render the
component and converts the data stored in a model object to types that can be
represented in a view.
•
A standard RenderKit for generating HTML/4.01 markup.
The following features support the GUI components:
•
Input validation
•
Event handling
•
Data conversion between model objects and components
•
Managed model object creation
•
Page navigation configuration
All this functionality is available via standard Java APIs and XML-based configuration files.
1.11.6 Java Message Service API
The Java Message Service (JMS) API is a messaging standard that allows Java EE application
components to create, send, receive, and read messages. It enables distributed communication
that is loosely coupled, reliable, and asynchronous.
1.11.7 Java Transaction API
The Java Transaction API (JTA) provides a standard interface for demarcating transactions.
The Java EE architecture provides a default auto commit to handle transaction commits and
rollbacks. An auto commit means that any other applications that are viewing data will see the
updated data after each database read or write operation. However, if your application performs
two separate database access operations that depend on each other, you will want to use the JTA
API to demarcate where the entire transaction, including both operations, begins, rolls back, and
commits.
1.11.8 JavaMail API
Java EE applications use the JavaMail API to send email notifications. The JavaMail API has
two parts: an application-level interface used by the application components to send mail, and a
service provider interface. The Java EE platform includes JavaMail with a service provider that
allows application components to send Internet mail.
1.11.9 JavaBeans Activation Framework
The JavaBeans Activation Framework (JAF) is included because JavaMail uses it. JAF
provides standard services to determine the type of an arbitrary piece of data, encapsulate access
to it, discover the operations available on it, and create the appropriate JavaBeans component to
11
1 - java platform, enterprise edition
perform those operations.
1.11.10 Java API for XML Processing
The Java API for XML Processing (JAXP), part of the Java SE platform, supports the
processing of XML documents using Document Object Model (DOM), Simple API for XML (SAX),
and Extensible Stylesheet Language Transformations (XSLT). JAXP enables applications to parse
and transform XML documents independent of a particular XML processing implementation.
JAXP also provides namespace support, which lets you work with schemas that might otherwise
have naming conflicts. Designed to be flexible, JAXP lets you use any XML-compliant parser or
XSL processor from within your application and supports the W3C schema. You can find
information on the W3C schema at this URL: http://www.w3.org/XML/Schema.
1.11.11 Java API for XML Web Services (JAX-WS)
The JAX-WS specification provides support for web services that use the JAXB API for binding
XML data to Java objects. The JAX-WS specification defines client APIs for accessing web
services as well as techniques for implementing web service endpoints. The Web Services for
J2EE specification describes the deployment of JAX-WS-based services and clients. The EJB
and servlet specifications also describe aspects of such deployment. It must be possible to deploy
JAX-WS-based applications using any of these deployment models.
The JAX-WS specification describes the support for message handlers that can process
message requests and responses. In general, these message handlers execute in the same
container and with the same privileges and execution context as the JAX-WS client or endpoint
component with which they are associated. These message handlers have access to the same
JNDI java:comp/env namespace as their associated component. Custom serializers and
deserializers, if supported, are treated in the same way as message handlers.
1.11.12 Java API for RESTful Web Services (JAX-RS)
The Java API for RESTful Web Services (JAX-RS) defines APIs for the development of Web
services built according to the Representational State Transfer (REST) architectural style. A JAXRS application is a web application that consists of classes that are packaged as a servlet in a
WAR file along with required libraries.
The JAX-RS API is new to the Java EE 6 platform.
1.11.13 Java Architecture for XML Binding (JAXB)
The Java Architecture for XML Binding (JAXB) provides a convenient way to bind an XML
schema to a representation in Java language programs. JAXB can be used independently or in
combination with JAX-WS, where it provides a standard data binding for web service messages.
All Java EE application client containers, web containers, and EJB containers support the JAXB
API.
1.11.14 SOAP with Attachments API for Java
The SOAP with Attachments API for Java (SAAJ) is a low-level API on which JAX-WS and
JAXR depend. SAAJ enables the production and consumption of messages that conform to the
SOAP 1.1 specification and SOAP with Attachments note. Most developers do not use the SAAJ
API, instead using the higher-level JAX-WS API.
1.11.15 Java API for XML Registries
The Java API for XML Registries (JAXR) lets you access business and general-purpose
registries over the web. JAXR supports the ebXML Registry and Repository standards and the
12
1 - java platform, enterprise edition
emerging UDDI specifications. By using JAXR, developers can learn a single API and gain access
to both of these important registry technologies.
Additionally, businesses can submit material to be shared and search for material that others
have submitted. Standards groups have developed schemas for particular kinds of XML
documents; two businesses might, for example, agree to use the schema for their industry's
standard purchase order form. Because the schema is stored in a standard business registry, both
parties can use JAXR to access it.
1.11.16 J2EE Connector Architecture
The J2EE Connector architecture is used by tools vendors and system integrators to create
resource adapters that support access to enterprise information systems that can be plugged in to
any Java EE product. A resource adapter is a software component that allows Java EE
application components to access and interact with the underlying resource manager of the EIS.
Because a resource adapter is specific to its resource manager, typically there is a different
resource adapter for each type of database or enterprise information system.
The J2EE Connector architecture also provides a performance-oriented, secure, scalable, and
message-based transactional integration of Java EE-based web services with existing EISs that
can be either synchronous or asynchronous. Existing applications and EISs integrated through the
J2EE Connector architecture into the Java EE platform can be exposed as XML-based web
services by using JAX-WS and Java EE component models. Thus JAX-WS and the J2EE
Connector architecture are complementary technologies for enterprise application integration
(EAI) and end-to-end business integration.
1.11.17 Java Database Connectivity API
The Java Database Connectivity (JDBC) API lets you invoke SQL commands from Java
programming language methods. You use the JDBC API in an enterprise bean when you have a
session bean access the database. You can also use the JDBC API from a servlet or a JSP page
to access the database directly without going through an enterprise bean.
The JDBC API has two parts: an application-level interface used by the application components
to access a database, and a service provider interface to attach a JDBC driver to the Java EE
platform.
1.11.18 Java Persistence API
The Java Persistence API is a new all Java standards based solution for persistence.
Persistence uses an object-relational mapping approach to bridge the gap between an object
oriented model and a relational database. Java Persistence consists of three areas:
•
The Java Persistence API
•
The query language
•
Object/relational mapping metadata
1.11.19 Java Naming and Directory Interface
The Java Naming and Directory Interface (JNDI) provides naming and directory functionality,
enabling applications to access multiple naming and directory services, including existing naming
and directory services such as LDAP (Lightweight Directory Access Protocol), NDS (Novell
Directory Services), DNS, and NIS (Network Information services). It provides applications with
methods for performing standard directory operations, such as associating attributes with objects
and searching for objects using their attributes. Using JNDI, a Java EE application can store and
retrieve any type of named Java object, allowing Java EE applications to coexist with many
legacy applications and systems.
13
1 - java platform, enterprise edition
Java EE naming services provide application clients, enterprise beans, and web components
with access to a JNDI naming environment. A naming environment allows a component to be
customized without the need to access or change the component's source code. A container
implements the component's environment and provides it to the component as a JNDI naming
context.
A Java EE component can locate its environment naming context using JNDI interfaces. A
component can create a javax.naming.InitialContext object and looks up the
environment naming context in InitialContext under the name java:comp/env. A
component's naming environment is stored directly in the environment naming context or in any
of its direct or indirect subcontexts.
A Java EE component can access named system-provided and user-defined objects. The
names of system-provided objects, such as JTA UserTransaction objects, are stored in the
environment naming context, java:comp/env. The Java EE platform allows a component to
name user-defined objects, such as enterprise beans, environment entries, JDBC DataSource
objects, and message connections. An object should be named within a subcontext of the naming
environment according to the type of the object. For example, enterprise beans are named within
the subcontext java:comp/env/ejb, and JDBC DataSource references in the subcontext
java:comp/env/jdbc.
1.11.20 Java Authentication and Authorization Service
The Java Authentication and Authorization Service (JAAS) provides a way for a Java EE
application to authenticate and authorize a specific user or group of users to run it.
JAAS is a Java programming language version of the standard Pluggable Authentication
Module (PAM) framework, which extends the Java Platform security architecture to support userbased authorization.
1.11.21 Java Authorization Service Provider Contract for Containers (Java
ACC)
The Java ACC specification defines a contract between a Java EE application server and an
authorization policy provider. All Java EE containers support this contract.
The Java ACC specification defines java.security.Permission classes that satisfy the
Java EE authorization model. The specification defines the binding of container access decisions
to operations on instances of these permission classes. It defines the semantics of policy
providers that employ the new permission classes to address the authorization requirements of
the Java EE platform, including the definition and use of roles.
1.11.22 Java Authentication Service Provider Interface for Containers
(JASPIC)
The Java Authentication Service Provider Interface for Containers (JASPIC) specification
defines a service provider interface (SPI) by which authentication providers that implement
message authentication mechanisms may be integrated in client or server message processing
containers or runtimes. Authentication providers integrated through this interface operate on
network messages provided to them by their calling container. They transform outgoing messages
so that the source of the message may be authenticated by the receiving container, and the
recipient of the message may be authenticated by the message sender. They authenticate
incoming messages and return to their calling container the identity established as a result of the
message authentication.
1.11.23 Simplified Systems Integration
The Java EE platform is a platform-independent, full systems integration solution that creates
14
1 - java platform, enterprise edition
an open marketplace in which every vendor can sell to every customer. Such a marketplace
encourages vendors to compete, not by trying to lock customers into their technologies but
instead by trying to outdo each other in providing products and services that benefit customers,
such as better performance, better tools, or better customer support.
The Java EE 6 APIs enable systems and applications integration through the following:
•
Unified application model across tiers with enterprise beans
•
Simplified request-and-response mechanism with JSP pages and servlets
•
Reliable security model with JAAS
•
XML-based data interchange integration with JAXP, SAAJ, and JAX-WS
•
Simplified interoperability with the J2EE Connector architecture
•
Easy database connectivity with the JDBC API
•
Enterprise application integration with message-driven beans and JMS, JTA, and JNDI
1.12 java EE application assembly and deployment
A Java EE application is packaged into one or more standard units for deployment to any Java
EE platform-compliant system. Each unit contains:
•
A functional component or components (such as an enterprise bean, JSP page, servlet, or
applet)
•
An optional deployment descriptor that describes its content
Once a Java EE unit has been produced, it is ready to be deployed. Deployment typically
involves using a platform’s deployment tool to specify location-specific information, such as a list
of local users that can access it and the name of the local database. Once deployed on a local
platform, the application is ready to run.
A Java EE application is delivered in an Enterprise Archive (EAR) file, a standard Java Archive
(JAR) file with an .ear extension. Using EAR files and modules makes it possible to assemble a
number of different Java EE applications using some of the same components. No extra coding is
needed; it is only a matter of assembling (or packaging) various Java EE modules into Java EE
EAR files.
An EAR file contains Java EE modules and deployment descriptors. A deployment descriptor
is an XML document with an .xml extension that describes the deployment settings of an
application, a module, or a component. Because deployment descriptor information is declarative,
it can be changed without the need to modify the source code. At runtime, the Java EE server
reads the deployment descriptor and acts upon the application, module, or component
accordingly.
15
1 - java platform, enterprise edition
Figure 1.6 EAR file structure
There are two types of deployment descriptors: Java EE and runtime. A Java EE deployment
descriptor is defined by a Java EE specification and can be used to configure deployment
settings on any Java EE-compliant implementation. A runtime deployment descriptor is used to
configure Java EE implementation-specific parameters. For example, the Sun Java System
Application Server Platform Edition 9 runtime deployment descriptor contains information such as
the context root of a web application, the mapping of portable names of an application’s resources
to the server’s resources, and Application Server implementation-specific parameters, such as
caching directives. The Application Server runtime deployment descriptors are named sunmoduleType.xml and are located in the same META-INF directory as the Java EE deployment
descriptor.
A Java EE module consists of one or more Java EE components for the same container type
and one component deployment descriptor of that type. An enterprise bean module deployment
descriptor, for example, declares transaction attributes and security authorizations for an
enterprise bean. A Java EE module without an application deployment descriptor can be deployed
as a stand-alone module.
The four types of Java EE modules are as follows:
•
EJB modules, which contain class files for enterprise beans and an EJB deployment
descriptor. EJB modules are packaged as JAR files with a .jar extension.
•
Web modules, which contain servlet class files, JSP files, supporting class files, GIF and
HTML files, and a web application deployment descriptor. Web modules are packaged as
JAR files with a .war (Web ARchive) extension.
•
Application client modules, which contain class files and an application client deployment
descriptor. Application client modules are packaged as JAR files with a .jar extension.
•
Resource adapter modules, which contain all Java interfaces, classes, native libraries,
and other documentation, along with the resource adapter deployment descriptor.
Together, these implement the Connector architecture (see J2EE Connector Architecture)
for a particular EIS. Resource adapter modules are packaged as JAR files with an .rar
(resource adapter archive) extension.
16
1 - java platform, enterprise edition
1.13 scripting versus application servers
In this section we attempt to answer a recurrent question – why bother with servlets, java server
pages or java server faces when we can achieve faster the same results using a versatile
language like PHP? Without ignoring its major qualities, let's point out some of weaknesses of
PHP, which are inherent to its nature.
PHP scripts are tied to a the web server and require writing explicit database queries to
generate dynamic content. Even these queries are written in a way which is specific to a particular
database engine. In PHP, the application programmer writes the SQL queries and embeds them
directly into the script, mixing presentation and business logic in the process. No direct support is
provided for the management of component pooling and lifecycle management, client session
management, database connection pooling, persistence, transaction management, authentication,
and access control. On the other hand, all these may be achieved through an application server.
17
2 - HTTP
2 - HTTP
2.1 what is http
HTTP stands for HyperText Transfer Protocol while hypertext means text contatining links to
another text. HTTP was created by by Tim Berners-Lee in 1990 at CERN as a mean to store
scientific data. It quickly evolved into the preferred communication protocol over the internet.
The first oficial version – HTTP 1.0 – dates from 05/95 and is the object of RFC 1945
(www.apps.ietf.org/rfc/rfc1945.html). It is authored by Tim Berners-Lee, Roy Fielding and Henrik
Nielsen.
The second (and last, so far) version, namely HTTP 1.1, was the object of several RFCs, of
which we mention RFC 2068 (01/97), RFC 2616 (06/99), RFC 2617 (06/99) and RFC 2774
(02/00).
For a complete specification of the different HTTP versions, check the official HTTP site –
www.w3.org/Protocols . As a site for understanding how HTTP works, we recommend
www.jmarshall.com/easy/http.
2.2 the structure of http transactions
HTTP follows the client – server model. The client sends a request message to the server. The
server answers with a response message. These messages may have different contents, but they
also have some common structural elements, as follows:
1. an initial line
2. zero or more header lines
3. a blank line (CR/LF)
4. an optional message body
<initial line>
Header1: value1
...
Headern: valuen
<optional data block>
2.3 the initial request line
Contains 3 elements, separated by spaces:
•
a command (method) name (like GET, POST, HEAD, ...)
•
a file specification (path) (the part of the URL after the host name)
18
2 - HTTP
the HTTP version (usually, HTTP/1.0).
•
Here is an example of an initial request line:
GET /path/to/the/file/index.html HTTP/1.0
2.4 http commands (methods)
As of HTTP 1.1, there are 8 HTTP commands (methods) that are widely supported. Here is
their list:
1. GET
2. HEAD
3. POST
4. CONNECT
5. DELETE
6. OPTIONS
7. PUT
8. TRACE
Three other commands are listed, as well, in the HTTP 1.1 specification, but lack of support
makes them obsolete. These commands are:
•
LINK
•
UNLINK
•
PATCH
The HEAD command is identical to the GET command in all respects but one. The only
difference is that the response must not have a body. All the information requested is returned in
the header section of the response.
2.5 the GET and POST methods
The GET method means retrieve whatever information (in the form of an entity) is identified by
the Request-URI. If the Request-URI refers to a data-producing process, it is the produced data
which shall be returned as the entity in the response and not the source text of the process, unless
that text happens to be the output of the process.
The POST method is used to request that the origin server accept the entity enclosed in the
request as a new subordinate of the resource identified by the Request-URI in the Request-Line.
POST is designed to allow a uniform method to cover the following functions:
- Annotation of existing resources;
- Posting a message to a bulletin board, newsgroup, mailing list,
19
2 - HTTP
or similar group of articles;
- Providing a block of data, such as the result of submitting a
form, to a data-handling process;
- Extending a database through an append operation.
The actual function performed by the POST method is determined by the server and is usually
dependent on the Request-URI. The posted entity is subordinate to that URI in the same way that
a file is subordinate to a directory containing it, a news article is subordinate to a newsgroup to
which it is posted, or a record is subordinate to a database.
The action performed by the POST method might not result in a resource that can be identified
by a URI. In this case, either 200 (OK) or 204 (No Content) is the appropriate response status,
depending on whether or not the response includes an entity that describes the result.
2.6 differences between GET and POST
1. The method GET is intended for getting (retrieving) data, while POST may involve anything,
like storing or updating data, or ordering a product, or sending E-mail
2. When used for form data submission, GET attaches this data to the URL of the request, after
the “?” character, as a sequence of “name=value” pairs, separated by the character “&” or “;”
On the other side, form data submitted by POST may be encoded either as above (using
application/x-www-form-urlencoded content type), or in the message
body, (encoded as multipart/form-data).
3. A POST request requires an extra transmission to retrieve the message body, while a GET
request allows data sent via the URL to be processed immediately.
2.7 the initial response (status) line
Contains 3 elements, separated by spaces (although the reason phrase may contain spaces, as
well):
•
the HTTP version of the response
•
a response status code (a number)
•
a response status reason phrase (a human readable response status)
Here is an example of an initial response line:
HTTP/1.0 404 Not Found
2.8 the status code
A three-digit integer, where the first digit identifies the general category of response:
•
1xx indicates an informational message only
20
2 - HTTP
•
2xx indicates success of some kind
•
3xx redirects the client to another URL
•
4xx indicates an error on the client's part
•
5xx indicates an error on the server's part
The most common status codes are:
•
200 OK - the request succeeded, and the resulting resource (e.g. file or script output) is
returned in the message body.
•
404 Not Found - the requested resource doesn't exist.
•
301 Moved Permanently
•
302 Moved Temporarily
•
303 See Other (HTTP 1.1 only) - the resource has moved to another URL (given by the
Location: response header), and should be automatically retrieved by the client. This is
often used by a CGI script to redirect the browser to an existing file.
•
500 Server Error - an unexpected server error. The most common cause is a server-side
script that has bad syntax, fails, or otherwise can't run correctly.
A complete list of status codes is in the HTTP specification (the URL was mentioned in the firs
section of this chapter) (section 9 for HTTP 1.0, and section 10 for HTTP 1.1).
2.9 header lines
A header line consists of two parts, header name and header value, separated a semicolon.
The HTTP 1.0 version specifies 16 headers, none of them mandatory, while the HTTP 1.1 version
specifies 46 of them, out of which, one (Host) is mandatory. Although the header names are not
case sensitive, header values are.
A couple of examples of header lines:
User-agent: Mozilla/3.0Gold
Last-Modified: Fri, 31 Dec 1999 23:59:59 GMT
Header lines which begin with spaces or tabs are parts of the previous header line.
2.10 the message body
An HTTP message may have a body of data sent after the header lines. The most common use
of the message body is in a response, that is, where the requested resource is returned to the
client, or perhaps explanatory text if there's an error. In a request, this is where user-entered data
or uploaded files are sent to the server.
If an HTTP message includes a body, the header lines of the message are used to describe the
body. In particular,
•
the Content-Type: header gives the MIME-type of the data in the body, such as text/html
or image/jpg.
•
the Content-Length: header gives the number of bytes in the body.
21
2 - HTTP
2.11 mime types/subtypes
MIME stands for Multipurpose Internet Mail Extensions. Each extension consists of a type and
a subtype. RFC 1521 (www.apps.ietf.org/rfc/rfc1521.html) defines 7 types and several subtypes,
although the list of admissible subtypes is much longer.
Here is the list of the seven types, together with the subtypes defined in this particular RFC.
1. text, with subtype plain
2. multipart, with subtypes mixed, alternative, digest, parallel
3. message, with subtypes rfc822, partial, external-body
4. application, with subtypes octet-stream, postscript
5. image, with subtypes jpeg, gif
6. audio, with subtype basic
7. video, with subtype mpeg
2.12 an example of an http transaction
To retrieve the file at the URL
http://web.info.uvt.ro/path/file.html
first open a socket to the host web.info.uvt.ro, port 80 (use the default port of 80 because none
is specified in the URL). Then, send something like the following through the socket:
GET /path/file.html HTTP/1.0
From: [email protected]
User-Agent: HTTPTool/1.0
[blank line here]
The server should respond with something like the following, sent back through the same
socket:
HTTP/1.0 200 OK
Date: Fri, 31 Dec 1999 23:59:59 GMT
Content-Type: text/html
Content-Length: 1354
<html>
<body>
<h1>Happy birthday!</h1>
(more file contents)
.
.
22
2 - HTTP
.
</body>
</html>
After sending the response, the server closes the socket.
23
3 - HTML
3 - HTML
3.1 what is html?
HTML stands for HyperText Markup Language. HTML describes how text, images and other
components are to be displayed in a browser, using a variety of tags and their related attributes.
The first version of HTML, namely HTML 1.0, appeared in summer 1991 and was supported by
the first popular web browser, Mosaic. The first official version – HTML 2.0 - was approved as a
standard in September 1995 (as RFC 1866 (http://www.apps.ietf.org/rfc/rfc1866.html) and was
widely supported. A newer standard, HTML 3.2 (3.0 was not widely accepted) appeared a W3C
recommendation in January 1997.
Version 4.0 introduces the Cascading Style Sheets.
The newest version of HTML is 4.01. It is a revision of 4.0 and was accepted in December
1997. However, a working draft for the next major revision, namely HTML 5 was published in
January 2008. Originally named Web Applications 1.0, the specification includes several ideas of
the WHAT (Web Hypertext Application Technology) working group. It might take several years
before the specification reaches final Recommendation status.
From 1999 on, HTML is part of a new specification – XHTML. The XHTML 1.0 draft was
released in 01.99. The latest version (XHTML 2.0) dates from 08.02 and is not intended to be
backwards compatible.
For a complete specification of the different HTML versions, check the official HTML site –
www.w3c.org/Markup . As a practical reference site use – www.blooberry.com/indexdot/html .
Other helpful sites - www.htmlgoodies.com/tutors, www.jmarshall.com/easy/html .
3.2 language definition
HTML is a system for describing documents. It is a special version of SGML (Standard
Generalized Markup Language – an ISO standard (ISO 8879)). All markup languages defined in
SGML are called SGML applications and are characterized by:
1. An SGML declaration – what characters and delimiters may appear. The SGML
declaration of the latest version of HTML (4.01) can be found at this address:
http://www.w3.org/TR/1999/PR-html40-19990824/sgml/sgmldecl.html. Since it fits in a
couple of pages, we can afford to have a look at this declaration.
<!SGML "ISO 8879:1986"
-SGML Declaration for HyperText Markup Language version HTML 4.01
With support for the first 17 planes of ISO 10646 and increased
limits for tag and literal lengths etc.
-CHARSET
BASESET
"ISO Registration Number 177//CHARSET
ISO/IEC 10646-1:1993 UCS-4 with
implementation level 3//ESC 2/5 2/15 4/6"
24
3 - HTML
DESCSET 0
9
11
13
14
32
127
128
160
55296
57344
CAPACITY
9
2
2
1
18
95
1
32
55136
2048
1056768
UNUSED
9
UNUSED
13
UNUSED
32
UNUSED
UNUSED
160
UNUSED
57344
SGMLREF
TOTALCAP
GRPCAP
ENTCAP
-- SURROGATES --
150000
150000
150000
SCOPE
DOCUMENT
SYNTAX
SHUNCHAR CONTROLS 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 127
BASESET "ISO 646IRV:1991//CHARSET
International Reference Version
(IRV)//ESC 2/8 4/2"
DESCSET 0 128 0
FUNCTION
NAMING
RE
RS
SPACE
TAB SEPCHAR
13
10
32
9
""
""
".-_:"
".-_:"
GENERAL YES
ENTITY NO
DELIM
GENERAL SGMLREF
SHORTREF SGMLREF
NAMES
SGMLREF
QUANTITY SGMLREF
ATTCNT
60
-- increased -ATTSPLEN 65536
-- These are the largest values
LITLEN
65536
-- permitted in the declaration
NAMELEN 65536
-- Avoid fixed limits in actual
PILEN
65536
-- implementations of HTML UA's
TAGLVL
100
TAGLEN
65536
GRPGTCNT 150
GRPCNT
64
FEATURES
MINIMIZE
DATATAG
OMITTAG
RANK
SHORTTAG
LINK
LCNMSTRT
UCNMSTRT
LCNMCHAR
UCNMCHAR
NAMECASE
-----
NO
YES
NO
YES
25
3 - HTML
>
SIMPLE
NO
IMPLICIT NO
EXPLICIT NO
OTHER
CONCUR
NO
SUBDOC
NO
FORMAL
YES
APPINFO NONE
2. A Document Type Definition (DTD) – defines the syntax of markup constructs. Check the
address http://www.w3.org/TR/REC-html40/sgml/dtd.html for the latest version of the
HTML DTD.
3. A specification that describes the semantics to be ascribed to the markup and character
entity references. This specification adds new syntactic restrictions which cannot be
defined within the frame of the DTD.
4. Document instances containing data (content) and markup. Each instance contains a
reference to the DTD to be used to interpret it.
Overall, the specification of HTML 4.0 contains an SGML declaration, three DTDs (HTML 4.0
Strict DTD, HTML 4.0 Transitional DTD, HTML 4.0 Frameset DTD) and a list of character
references. If you wonder what a character reference is, look at these examples: “&lt”, “&quot”,
"&#x6C34;" (in hexadecimal) - the chinese character for water. You get the point.
3.3 html elements
An HTML element consists of:
•
a start tag
•
a content
•
an end tag
One exception, though; the element <BR> has no content and no end tag.
There are 91 elements defined in the HTML 4.01 specification. This section deals with some of
the most common elements.
The start tag of the element contains the values of the (required or optional) attributes of the
element. An example:
<IMG SRC=”/images/logo.gif” ALT=”logo” HEIGHT=40 WIDTH=120>
declares an image element, with the required (mandatory) attributes SRC and ALT and the
optional attributes HEIGHT and WIDTH. Other optional attributes of the <IMG> element, like
ALIGN, BORDER, CONTROLS, DYNSRC, …, VSAPCE are omitted.
A comment section in an HTML document starts with <!-- and end at the first occurrence of -->.
An example:
<!-- acesta este un comentariu. <><> -->
26
3 - HTML
3.3.1 The <A> element
Must contain one of the 2 attributes – HREF, NAME. Main attributes:
•
HREF – specifies the absolute or relative URL of the hyperlink
•
NAME – assigns a symbolic name to the enclosed object (text, image, etc.) in order to
use it as a destination in a hyperlink or another URL call.
Example:
<A HREF=”http://web.info.uvt.ro/webmail/src/login.php”>Login to
web mail</A>
3.3.2 The <IMG> element
Main attributes:
•
ALT – required; specifies the text to be displayed in case source is not found
•
SRC – required; indicates the URL to reference the graphic
•
HEIGHT
•
WIDTH
3.4 the minimal structure of an html document
All HTML documents start with the <HTML> tag and end with the corresponding end tag
</HTML>. An HTML document consists of the parts:
•
the <HEAD> part
•
the <BODY> part
A minimal HTML document example:
<HTML>
<HEAD>My Page
</HEAD>
<BODY>Empty Body
</BODY>
</HTML>
3.5 tables
27
3 - HTML
A table is a visual rectangular object consisting of several rows and columns. The intersection
of any row and any column is called a cell. Usually, the cells in the first row contain are called
headers and consist of a brief description of the content of the corresponding column. Here is a
an example of a table:
3.6 table related elements
The specific elements defining a table, its rows, columns, headers and cells are <TABLE>,
<THEAD>, <TR>, <TH> and <TD>. Here is their description and attributes.
the <TABLE> element
attributes:
•
BORDER
•
CELLSPACING
•
CELLPADDING
•
WIDTH
•
ALIGN
•
VALIGN
•
TBODY
•
BORDERCOLOR
•
FRAME
•
RULES
•
COLORGROUP
•
BACKGROUND
the <THEAD> element
attributes:
•
ALIGN
•
BGCOLOR
•
CHAR
•
CHAROFF
28
3 - HTML
•
VALIGN
the <TH> element
attributes:
•
ABBR
•
AXIS
•
CHAR
•
CHAROFF
•
HEADERS
•
SCOPE
the <TR> element
attributes:
•
ALIGN
•
BGCOLOR
•
CHAR
•
CHAROFF
•
VALIGN
the <TD> element
attributes:
•
ABBR
•
ALIGN
•
CHAR
•
CHAROFF
•
COLSPAN
•
ROWSPAN
•
SCOPE
•
VALIGN
•
WIDTH
3.7 forms
A form is a basic component container, allowing user input and parameter submittal.
The <FORM> element has the following attributes:
•
ACTION - required, specifies the URL of the server side process that will receive the data
29
3 - HTML
•
METHOD - required, may have the values GET or POST, specifies how data will be sent to
the server. Possible values for this attribute:
•
"POST"- sends the form values in 2 steps: contacts first the server then the form values are
sent in a separate transmission.
•
"GET" - sends the form values in a single transmission, the browser appends the values to
the URL, after a quotation mark - ?. The pairs name=value are separated by ampersand - &
or (sometimes) by semicolon - :.
Example:
http://web.info.uvt.ro/servlet/MyServlet?a=12&b=25
•
ENCTYPE - specifies the encoding type of the of the form content. Default value:
"application/x-www-form-urlencoded" - the default value; however, since it converts spaces
to '+' and non-alphanumerical to '%HH', where 'HH' is the hexadecimal ASCII code of the
character.
•
Other possible values for this attribute:
•
"multipart/form-data" - used with forms that contain a file-selection field, data is sent as a
single document with multiple sections.
•
"text/plain"
3.8 form related elements
3.8.1 the <INPUT> element
Defines input fields for the form. Main attributes:
•
TYPE - required, specifies the type of the input which can have one of the following
values: "text", "password", "checkbox", "radio", "submit", "image", "reset", "button",
"hidden", "file".
•
NAME - required, specifies the parameter name.
3.8.2 the <SELECT> element
Used to create a list of choices, either as a drop-down menu or as a list box. Each of the listed
choices is an OPTION element.
Main attributes:
•
NAME
•
MULTIPLE - if specified, allows multiple selections from the choice list.
•
SIZE - maximum number of options visible to the user.
3.8.3 the <OPTION> element
Used inside a <SELECT> element to list the selection choices. Main attributes:
30
3 - HTML
•
SELECTED
Example of a <SELECT> element:
<SELECT NAME="action" STYLE="font-family: '@Arial Unicode
MS' font-size: 11pt">
<OPTION SELECTED>Select Action
<OPTION>Make Payment
<OPTION>Transfer a balance
<OPTION>Change Mailing Address
<OPTION>Change e-mail Address
<OPTION>Change User Name/Password
<OPTION>View Account Activity
</SELECT>
31
4 - JAVA PRIMER
4 - JAVA PRIMER
4.1 history
The initial name of this language was OAK and was developed as part of the GREEN project at
Sun, project started in 12.90. Early versions of Java were released in 12.94 and was officially
announced at Sun World in 05.95. The first commercial version was delivered to the first
customer (Netscape, Inc.) in 08.95. The current version (as of 10.2004) of Java 2 Platform
Standard Edition is J2SE 5.0, following the 1.4.2 version. The current version (as of 10.2010) of
Java Platform Enterprise Edition is Java EE 6 Update 21.
4.2 java the interpreter, jit
From source to execution, A java program goes thru the following phases:
1. Java source – a file with extension .java
2. Java bytecode – a file with extension .class
3. The Java interpreter (which is part of the Java Virtual Machine) parses and executes the
Java bytecode.
Example:
Edit the file prog1.java. The java compiler (javac) translates it to bytecode – prog1.class. The
java interpreter (as part of the JVM) parses and executes the prog1.class file.
In terms of execution time, a Java interpreted program is about 10 times slower than a
compiled and linked one. To overcome this significant shortage, a tool named Just In Time
compiler, allows the compilation of the Java source into machine-dependent binary executable.
The first time a class is loaded, the compilation process occurs, which accounts for a pretty slow
execution, but next time execution is much faster, pretty much comparable to that of a binary
executable.
The java compiler is (in general) a command line tool, with the following main options:
•
-classpath <path>
•
-sourcepath <path>
•
-d <directory> : specifies where to put the .class file.
•
-g : generate all debugging info.
One example of command line compilation:
javac -classpath .;C:\TW\mySource;C:\TW\myPackages -g login.java
4.3 java applications
32
4 - JAVA PRIMER
There exist 2 types of programs that can be written in Java. The first type are embedded in web
pages – applets, the others are the standalone programs – Java applications.
A java applet is a java class that extends the standard Applet class.
In general, an applet is inserted in a HTML page by an <APPLET> tag or by an <OBJECT> tag.
The <APPLET> element has 3 mandatory attributes, namely:
•
CODE – identifies the (compiled) class file of the applet
•
WIDTH
•
HEIGHT
A java application is a collection of java classes. Generally, each class is implemented in a
source file having the same name as the class itself and whose extension is .java. Exactly one of
these classes must implement a method called main(). This method is the entry point in the
application and must have the following signature:
public static void main(String[] args)
A compiled java application (class) may be executed from the command line using an
executable called java (the java interpreter), as follows:
java [-options] class [args]
Where main options are:
•
-cp <directories and jar files separated by “;”> : cp = classpath
•
-D <name>=<value> : set a system property
To execute a .jar file, use the command:
java –jar [-options] jarfile [args]
4.4 object oriented concepts
4.4.1 encapsulation
This is a fancy word for the tendency of hiding the implementation of the methods of some
class and exposing only the interface of its public (and to some degree – its protected) methods.
4.4.2 inheritance
Inheritance is a partial order relation in the set of all Java classes. A Java class B inherits
another class A (or is a subclass of A, or is derived from A, or that it extends A). This binary
relation is specified in the declaration of the derived class B using the keyword extends. An
example:
33
4 - JAVA PRIMER
public class CaineComunitar extends Caine
{
…
}
In this case, all variables and methods of the base class A are automatically variables and
methods of the derived class B.
The derived class B can use (for free) all the methods of the base class, but it also can
override the implementation of any method in the base class, providing its own implementation.
While C++ allows multiple inheritance, a Java class can extend a single base class. That
means that the graph of the direct inheritance relation is a forest (its connected components are
trees). In fact, all classes in Java are (by default) subclasses of a universal base class, called
Object. Therefore, the forest we mentioned is actually a tree, with the root the class Object.
4.4.3 Polymorphism
Polymorphism means the ability of a variable of a given (base) type (class) to be used to
reference objects of different (derived) types (classes), and automatically call the method specific
to the type (derived class) of the object that the variable references.
4.4.4 Method overloading
A method (which has to be declared in some class (or interface)) is identified by its name and
the type sequence of its parameters. The return type of a method is not part of this signature.
Therefore, a class can have more than one method with the same name, provided that the types
(and order) of its parameters are different. In OO jargon, this is called method overloading.
4.5 java as programming language
integer data types:
•
byte
•
short
•
int
•
long
floating point data types:
•
float
•
double
other types:
•
boolean - 1 bit
•
char - Unicode (16 bits)
All basic types have associated classes which extend their functionality, namely: Byte, Short,
Integer, Long, Float, Double, Boolean, Character.
34
4 - JAVA PRIMER
Other peculiarities: no pointers (only references), automatic garbage collection, no templates.
4.6 access specifiers and modifiers in java
The access attributes of a member variable or method of a class are specified by the access
specifiers. Except for the "package" concept, they have the same basic meaning as in C++.
•
no specifier - the default value allows access from any class in the same package
•
public - access from any class anywhere
•
private - no access from outside the class itself
•
protected - accessible from any class in the same package an any subclass anywhere
While the above specifiers apply to the variables and the methods of a class, the specifiers for
the class itself can be taken from the following list:
•
no specifier - the default value makes the class visible only to the classes in the same
package
•
public - the class is visible from any class, anywhere
•
abstract - the class is abstract (some of its methods (inherited or specified by some
interface) are to be implemented by some of its subclasses)
An example. The declaration:
abstract class myFirstClass extends javax.servlet.http.HttpServlet
implements Serializable
{
...
}
declares an abstract class, which is visible only to the classes in the same package, which
extends the class javax.servlet.http.HttpServlet and which implements the
Serializable interface.
The modifiers of the variables and methods of a class specify their range and stability. A static
variable or method is one which is implemented at class level, rather than at class instance. A
final variable (method, class) is one which cannot be modified (overridden, inherited). More
precisely:
A static (or class):
•
variable - one which is defined at class level, has the same value for all class instances.
•
method - all variables referenced in the function body are static variables.
Static variables and methods can be referenced (invoked) using either the name of the class or
the name of a class instance.
A final:
•
variable - one which is constant
•
method - the method implementation cannot be overriden by some subclass.
•
class - does not have any subclasses.
35
4 - JAVA PRIMER
4.7 exceptions in java
An exception signals an abnormal situation or an error in an application, due to a variety of
execution factors or due to programming errors.
In Java, an exception is an object which is created when the abnormal situation occurs.
Exception categories:
1. code or data errors - like invalid cast, array index out of bounds, division by 0.
2. standard method exceptions
3. programmer defined exceptions
4. java errors - JVM execution errors (mostly caused by programming errors).
All exceptions (even programmer defined) must inherit from the standard class Throwable.
All the standard exceptions are derived from 2 direct subclasses of Throwable, namely class
Error and the class Exception.
4.7.1 The Error class
Represent conditions which are not expected to be caught in our code. Therte are 3 direct
subclasses of the class Error - ThreadDeath, Linkage Error and VirtualMachineError.
4.7.2 The Exception class
Except for the RuntimeException exceptions, all then exceptions in this category must be
caught in our code.
4.7.3 RuntimeException Exceptions
Usually, these exceptions take place because of serious code errors and they are supposed to
be fixed in the coding phase, not at execution time.
The subclasses of the RuntimeException class, as defined in the java.lang package are:
•
•
•
•
•
•
•
•
•
•
•
ArithmeticException
IndexOutOfBoundException
NegativeArraySizeException
NullPointerException
ArrayStoreException
ClassCastException
IllegalArgumentException
SecurityException
IllegalMonitorStateException
IllegalStateException
UnsupportedOperationException
4.7.4 Handling Exceptions
There are 2 ways to deal with exceptions:
36
4 - JAVA PRIMER
•
supply then code to deal with the exception inside the method - this can be done by
providing a try, catch, finally construct.
•
ignore it (pass it to the code that called the method) - by adding the key word throws,
followed by a comma separated list of exceptions after the parameter list of the method.
4.8 java packages
A Java package is a named collection of classes. Each class belongs to a package (even if a
package name is not specified, the default package is used). The names in a package are
qualified by the package name, therefore, they have to be unique inside a package.
4.8.1 Package names
The default package has no name. The package containing the standard classes is java.lang
(automatically available). All other packages must be explicitly imported. As a general rule, the
package statement is the first one in a java source file, followed by the import statements. An
example:
package com.bank11.ccards.servlets;
import javax.sql.*;
import.java.util.Properties;
...
The name of the package is directly linked to the directory structure in which it is stored. In the
example above, the class (the .class file, rather) defined in the java source must be stored in a
directory called servlets, which is a subdirectory of ccards (which itself, is a subdirectory of a
directory called bank11).
4.9 standard Java packages
•
java.lang - default, don't have to import
•
java.io
•
java.awt - support for user interface
•
java.awt.event - support for event handling
•
java.awt.geom - support for operations with 2D geometric figures
•
java.net
•
java.nio
•
java.rmi
•
java.util - support for data collections, string analyzers, date and time info
•
java.util.zip - support for java archives creation
•
java.sql
•
java.security
37
4 - JAVA PRIMER
•
java.text
•
javax.accessibility
•
javax.swing - swing GUI components (minimal dependence on native code)
•
java.swing.event - support for event handling
4.10 interfaces
An interface in Java corresponds to the abstract class concept in C++. While multiple
inheritance is forbidden in Java (a class can be the subclass of a single base class), Java classes
can implement zero or more interfaces.
An interface is a collection of constants and "abstract" functions.
All variables (actually, constants) of an interface are automatically (by default) public, static and
final. All methods declared in an interface are (by default) public and abstract.
If a class is declared as implementing an interface but omits some of its methods, it must be
declared as abstract.
38
5 - javaScript
5 - JAVASCRIPT
5.1 so what is JavaScript?
JavaScript is a scripting language designed to add interactivity to HTML pages.
•
•
•
•
A scripting language is a lightweight programming language
A JavaScript source consists of lines of executable computer code
A JavaScript is usually embedded directly into HTML pages
JavaScript is an interpreted language (means that scripts execute without preliminary
compilation)
The initial official name of this language was ECMAscript. ECMA stands for European
Computer Manufacturers Association and is an organization founded in 1961 to standardize
computer systems in Europe. The origins of this language date back to 1995, and was originally
developed by Brendan Eich of Netscape under the names Mocha, then LiveScript and finally, as
JavaScript. Subsequently, JavaScript was standardized by ECMA in June 1997 under the name
ECMAScript. However, the general public knows it only by the name given by its creator –
JavaScript. Adaptations of the ECMA standard for other applications, like KDE or Adobe Flash
bear different names, like QtScript or ActionScript.
5.2 what can a JavaScript do?
•
•
•
•
•
•
•
JavaScript gives HTML designers a programming tool - HTML authors are normally
not programmers, but JavaScript is a scripting language with a very simple syntax!
Almost anyone can put small "snippets" of code into their HTML pages
JavaScript can put dynamic text into an HTML page - A JavaScript statement like this:
document.write("<h1>" + name + "</h1>") can write a variable text into an HTML page
JavaScript can react to events - A JavaScript can be set to execute when something
happens, like when a page has finished loading or when a user clicks on an HTML
element
JavaScript can read and write HTML elements - A JavaScript can read and change the
content of an HTML element
JavaScript can be used to validate data - A JavaScript can be used to validate form
data before it is submitted to a server. This saves the server from extra processing
JavaScript can be used to detect the visitor's browser - A JavaScript can be used to
detect the visitor's browser, and - depending on the browser - load another page
specifically designed for that browser
JavaScript can be used to create cookies - A JavaScript can be used to store and
retrieve information on the visitor's computer
5.3 how and where?
JavaScripts in a page will be executed immediately while the page loads into the browser. This
is not always what we want. Sometimes we want to execute a script when a page loads, other
39
5 - javaScript
times when a user triggers an event.
5.3.1 scripts in the head section
Scripts to be executed when they are called, or when an event is triggered, go in the head
section. When you place a script in the head section, you will ensure that the script is loaded
before anyone uses it. Here is an example:
<html>
<head>
<script type="text/javascript">
....
</script>
</head>
5.3.2 scripts in the body section
Scripts which are to be executed when the page loads go in the body section. When you place
a script in the body section it generates the content of the page.
<html>
<head>
</head>
<body>
<script type="text/javascript">
....
</script>
</body>
5.3.3 using an external JavaScript
Sometimes you might want to run the same JavaScript on several pages, without having to
write the same script on every page. To simplify this, you can write a JavaScript in an external
file.
Save the external JavaScript file with a .js file extension.
Note: The external script cannot contain the <script> tag!
To use the external script, point to the .js file in the "src" attribute of the <script> tag:
<html>
<head>
<script src="myScript.js">
</script>
</head>
<body>
</body>
</html>
5.4 javaScript variables and expressions
A variable is a "container" for some information whose value can change during the script.
40
5 - javaScript
5.4.1 variable names
Rules for variable names:
•
•
Variable names are case sensitive
They must begin with a letter or the underscore character
5.4.2 variable declaration
A variable can be declared or even created with the var statement:
var strnum = "2157 Sunrise Blvd";
or
strnum = "2157 Sunrise Blvd";
5.4.3 variable assignment
A value can be assigned to a variable at declaration time:
var strnum = "Morii 771"
Or just use a plain assignment:
strname = "Morii 771"
5.4.4 variable types
A variable declaration in JavaScript does not contain a type declaration. The type of the
variable is determined by any assignment of a value to that variable. This means that the type of
the variable can change during the execution of a JavaScript script.
5.5 javaScript flow control
Apart from the usual flow control constructs, namely – if ... else, switch(), for(), while(), break,
continue, while() it is worth mentioning the for ... in and the try ... catch constructs.
5.5.1 JavaScript for...In statement
The for...in statement is used to loop (iterate) through the elements of an array or through the
properties of an object.
The code in the body of the for ... in loop is executed once for each element/property.
Syntax
for (variable in object)
{
code to be executed
}
41
5 - javaScript
The variable argument can be a named variable, an array element, or a property of an object.
Example
Using for...in to loop through an array:
<html>
<body>
<script type="text/javascript">
var x;
var mycars = new Array();
mycars[0] = "Saab";
mycars[1] = "Volvo";
mycars[2] = "BMW";
for (x in mycars)
{
document.write(mycars[x] + "<br />");
}
</script>
</body>
</html>
5.5.2 catching errors
When browsing Web pages on the internet, we all have seen a JavaScript alert box telling us
there is a runtime error and asking "Do you wish to debug?". Error message like this may be
useful for developers but not for users. When users see errors, they often leave the Web page.
This chapter will teach you how to trap and handle JavaScript error messages, so you don't lose
your audience.
There are two ways of catching errors in a Web page:
•
•
By using the try...catch statement (available in IE5+, Mozilla 1.0, and Netscape 6)
By using the onerror event. This is the old standard solution to catch errors (available
since Netscape 3)
5.5.3 try...catch statement
The try...catch statement allows you to test a block of code for errors. The try block contains the
code to be run, and the catch block contains the code to be executed if an error occurs.
Syntax
try
{
// run some code here
}
catch(err)
{
42
5 - javaScript
// handle errors here
}
Example
<html>
<head>
<script type="text/javascript">
var txt=""
function message()
{
try
{
adddlert("Welcome guest!");
}
catch(err)
{
txt="There was an error on this page.\n\n";
txt+="Error description: " + err.description + "\n\n";
txt+="Click OK to continue.\n\n";
alert(txt);
}
}
</script>
</head>
<body>
<input type="button" value="View message" onclick="message()" />
</body>
</html>
5.6 operators
The only new one is the comparison operator === (equal values and same type). Also, strings
can be added (concateneted) using the + operator.
5.7 popup boxes
5.7.1 alert Box
An alert box is often used if you want to make sure information comes through to the user.
When an alert box pops up, the user will have to click "OK" to proceed.
Syntax:
43
5 - javaScript
alert("sometext")
5.7.2 confirm Box
A confirm box is often used if you want the user to verify or accept something. When a confirm
box pops up, the user will have to click either "OK" or "Cancel" to proceed. If the user clicks "OK",
the box returns true. If the user clicks "Cancel", the box returns false.
Syntax:
confirm("sometext")
5.7.3 prompt Box
A prompt box is often used if you want the user to input a value before entering a page. When a
prompt box pops up, the user will have to click either "OK" or "Cancel" to proceed after entering
an input value. If the user clicks "OK" the box returns the input value. If the user clicks "Cancel",
the box returns null.
Syntax:
prompt("sometext","defaultvalue")
5.8 functions
5.8.1 function definition
A function contains some code that will be executed only by an event or by a call to that
function. A function can be called from anywhere within the page (or even from other pages if the
function is embedded in an external .js file). Functions are defined at the beginning of a page, in
the <head> section. Example:
<html>
<head>
<script type="text/javascript">
function displaymessage() { alert("Hello World!") }
</script>
</head>
<body>
<form>
<input type="button" value="Click me!"
onclick="displaymessage()" >
</form>
</body>
</html>
If the line: alert("Hello world!!"), in the example above had not been written within a function, it
would have been executed as soon as the line was loaded. Now, the script is not executed before
the user hits the button. We have added an onClick event to the button that will execute the
function displaymessage() when the button is clicked..
The syntax for creating a function is:
44
5 - javaScript
function functionname(var1,var2,...,varX) { some code }
var1, var2, etc are variables or values passed into the function. The { and the } defines the start
and end of the function.
function functionname() { some code }
Note: Do not forget about the importance of capitals in JavaScript! The word function must be
written in lowercase letters, otherwise a JavaScript error occurs! Also note that you must call a
function with the exact same capitals as in the function name.
5.8.2 the return statement
The return statement is used to specify the value that is returned from the function. So,
functions that are going to return a value must use the return statement. An example is the
function below should return the product of two numbers (a and b):
function prod(a,b) { x=a*b return x }
When you call the function above, you must pass along two parameters:
product=prod(2,3)
The returned value from the prod() function is 6, and will be stored in the variable called product.
5.9 javaScript objects
5.9.1 object oriented programming
JavaScript is an Object Oriented Programming (OOP) language. An OOP language allows you
to define your own objects and make your own variable types.
We will start by looking at the built-in JavaScript objects, and how they are used. The next
pages will explain each built-in JavaScript object in detail.
5.9.2 properties
Properties are the values associated with an object.
In the following example we are using the length property of the String object to return the
number of characters in a string:
<script type="text/javascript">
var txt="Hello World!";
document.write(txt.length);
</script>
The output of the code above will be:
12
45
5 - javaScript
5.9.3 methods
Methods are the actions that can be performed on objects.
In the following example we are using the toUpperCase() method of the String object to display
a text in uppercase letters:
<script type="text/javascript">
var str="Hello world!";
document.write(str.toUpperCase());
</script>
5.10 the hierarchy of javaScript browser objects
There are two major classes of built-in javascript objects. The first class consists of browser
specific objects. The other class are the language specific objects, which will be specified in the
next section.
46
5 - javaScript
We can think of each Web page as a collection of several individual elements, which are called
Objects. For example, every Image on the page is an Object, every Link on the page is an Object.
Even this Document itself is an Object. At its most basic level, JavaScript allows you to control
the appearance of many of the Objects that make up a Web page as we previously saw.
Objects are storage containers that have Properties (data values associated with Objects) and
Methods (functions associated with Objects) that operate on that data. Objects may also have
certain Events that are associated with them. Events are special signals or messages which occur
when certain pre-defined actions take place within a Web browser, or when the user interacts with
a Web page. When an event message has been triggered, you need a way to intercept the
message and react to it. This is achieved through the use of Event Handlers.
For an exhaustive list of properties and methods of the above objects (and for the built in
objects, as well), check the site http://www.w3schools.com/jsref/default.asp
5.11 javaScript language built in objects
5.11.1 the String object
The String object is used to manipulate a stored piece of text.
Properties
FF: Firefox, N: Netscape, IE: Internet Explorer
Property
Description
F
N
F
I
E
constructor
A reference to the function that created the object
1
4
4
length
Returns the number of characters in a string
1
2
3
prototype
Allows you to add properties and methods to the object
1
2
4
F
N
Methods
Method
Description
F
I
E
anchor()
Creates an HTML anchor
1
2
3
big()
Displays a string in a big font
1
2
3
blink()
Displays a blinking string
1
2
bold()
Displays a string in bold
1
2
3
charAt()
Returns the character at a specified position
1
2
3
charCodeAt()
Returns the Unicode of the character at a specified position
1
4
4
concat()
Joins two or more strings
1
4
4
fixed()
Displays a string as teletype text
1
2
3
fontcolor()
Displays a string in a specified color
1
2
3
fontsize()
Displays a string in a specified size
1
2
3
fromCharCode()
Takes the specified Unicode values and returns a string
1
4
4
47
5 - javaScript
indexOf()
italics()
lastIndexOf()
Returns the position of the first occurrence of a specified
string value in a string
Displays a string in italic
Returns the position of the last occurrence of a specified
string value, searching backwards from the specified position
in a string
1
2
3
1
2
3
1
2
3
link()
Displays a string as a hyperlink
1
2
3
match()
Searches for a specified value in a string
1
4
4
1
4
4
1
4
4
1
4
4
replace()
search()
slice()
Replaces some characters with some other characters in a
string
Searches a string for a specified value
Extracts a part of a string and returns the extracted part in a
new string
small()
Displays a string in a small font
1
2
3
split()
Splits a string into an array of strings
1
4
4
strike()
Displays a string with a strikethrough
1
2
3
sub()
Displays a string as subscript
1
2
3
substr()
Extracts a specified number of characters in a string, from a
start index
1
4
4
substring()
Extracts the characters in a string between two specified
indices
1
2
3
sup()
Displays a string as superscript
1
2
3
toLowerCase()
Displays a string in lowercase letters
1
2
3
toUpperCase()
Displays a string in uppercase letters
1
2
3
toSource()
Represents the source code of an object
1
4
-
valueOf()
Returns the primitive value of a String object
1
2
4
5.11.2 the Date object
The JavaScript Date object is used to work with dates and times.
Properties
FF: Firefox, N: Netscape, IE: Internet Explorer
Property
constructor
prototype
Description
F
F
Returns a reference to the Date function that created
the object
Allows you to add properties and methods to the object
N
I
E
1
4
4
1
3
4
Methods
Method
Description
Date()
Returns today's date and time
F
F
1
N
2
I
E
3
48
5 - javaScript
getDate()
Returns the day of the month from a Date object (from
1-31)
getDay()
Returns the day of the week from a Date object (from 0-
1
2
3
1
2
3
1
4
4
6)
getFullYear()
Returns the year, as a four-digit number, from a Date
object
getHours()
Returns the hour of a Date object (from 0-23)
1
2
3
getMilliseconds()
Returns the milliseconds of a Date object (from 0-999)
1
4
4
getMinutes()
Returns the minutes of a Date object (from 0-59)
1
2
3
getMonth()
Returns the month from a Date object (from 0-11)
1
2
3
getSeconds()
Returns the seconds of a Date object (from 0-59)
1
2
3
getTime()
Returns the number of milliseconds since midnight Jan
1, 1970
1
2
3
getTimezoneOffset()
Returns the difference in minutes between local time
and Greenwich Mean Time (GMT)
1
2
3
getUTCDate()
Returns the day of the month from a Date object
according to universal time (from 1-31)
1
4
4
getUTCDay()
Returns the day of the week from a Date object
according to universal time (from 0-6)
1
4
4
getUTCMonth()
Returns the month from a Date object according to
universal time (from 0-11)
1
4
4
getUTCFullYear()
Returns the four-digit year from a Date object according
to universal time
1
4
4
getUTCHours()
Returns the hour of a Date object according to universal
time (from 0-23)
1
4
4
getUTCMinutes()
Returns the minutes of a Date object according to
universal time (from 0-59)
1
4
4
getUTCSeconds()
Returns the seconds of a Date object according to
universal time (from 0-59)
1
4
4
getUTCMilliseconds()
Returns the milliseconds of a Date object according to
universal time (from 0-999)
1
4
4
getYear()
Returns the year, as a two-digit or a three/four-digit
number, depending on the browser. Use getFullYear()
instead !!
1
2
3
parse()
Takes a date string and returns the number of
milliseconds since midnight of January 1, 1970
1
2
3
setDate()
Sets the day of the month in a Date object (from 1-31)
1
2
3
setFullYear()
Sets the year in a Date object (four digits)
1
4
4
setHours()
Sets the hour in a Date object (from 0-23)
1
2
3
setMilliseconds()
Sets the milliseconds in a Date object (from 0-999)
1
4
4
setMinutes()
Set the minutes in a Date object (from 0-59)
1
2
3
setMonth()
Sets the month in a Date object (from 0-11)
1
2
3
setSeconds()
Sets the seconds in a Date object (from 0-59)
1
2
3
1
2
3
setTime()
Calculates a date and time by adding or subtracting a
specified number of milliseconds to/from midnight January
1, 1970
49
5 - javaScript
setUTCDate()
Sets the day of the month in a Date object according to
universal time (from 1-31)
1
4
4
setUTCMonth()
Sets the month in a Date object according to universal
time (from 0-11)
1
4
4
setUTCFullYear()
Sets the year in a Date object according to universal
time (four digits)
1
4
4
setUTCHours()
Sets the hour in a Date object according to universal
time (from 0-23)
1
4
4
setUTCMinutes()
Set the minutes in a Date object according to universal
time (from 0-59)
1
4
4
setUTCSeconds()
Set the seconds in a Date object according to universal
time (from 0-59)
1
4
4
setUTCMilliseconds()
Sets the milliseconds in a Date object according to
universal time (from 0-999)
1
4
4
setYear()
Sets the year in the Date object (two or four digits). Use
setFullYear() instead !!
1
2
3
toDateString()
Returns the date portion of a Date object in readable
form
toGMTString()
Converts a Date object, according to Greenwich time, to
a string. Use toUTCString() instead !!
1
2
3
toLocaleDateString()
Converts a Date object, according to local time, to a
string and returns the date portion
1
4
4
toLocaleTimeString()
Converts a Date object, according to local time, to a
string and returns the time portion
1
4
4
toLocaleString()
Converts a Date object, according to local time, to a
string
1
2
3
toSource()
Represents the source code of an object
1
4
-
toString()
Converts a Date object to a string
1
2
4
toTimeString()
Returns the time portion of a Date object in readable
form
toUTCString()
Converts a Date object, according to universal time, to a
string
1
4
4
UTC()
Takes a date and returns the number of milliseconds
since midnight of January 1, 1970 according to universal
time
1
2
3
1
2
4
valueOf()
Returns the primitive value of a Date object
5.11.3 the Array object
The JavaScript Array object is used to store a set of values in a single variable name.
Properties
FF: Firefox, N: Netscape, IE: Internet Explorer
Property
Description
F
F
N
I
E
50
5 - javaScript
constructor
Returns a reference to the array function that created the
object
index
input
1
2
4
1
3
4
1
3
4
length
Sets or returns the number of elements in an array
1
2
4
prototype
Allows you to add properties and methods to the object
1
2
4
F
N
Methods
Method
Description
F
concat()
join()
pop()
Joins two or more arrays and returns the result
Puts all the elements of an array into a string. The elements
are separated by a specified delimiter
Removes and returns the last element of an array
I
E
1
4
4
1
3
4
1
4
5
.5
push()
Adds one or more elements to the end of an array and returns
the new length
1
4
5
.5
reverse()
Reverses the order of the elements in an array
1
3
shift()
Removes and returns the first element of an array
1
4
4
5
.5
slice()
Returns selected elements from an existing array
1
4
4
sort()
Sorts the elements of an array
1
3
4
splice()
Removes and adds new elements to an array
1
4
5
.5
toSource()
Represents the source code of an object
1
4
-
toString()
Converts an array to a string and returns the result
1
3
4
1
4
6
1
2
4
unshift()
valueOf()
Adds one or more elements to the beginning of an array and
returns the new length
Returns the primitive value of an Array object
5.11.4 the Number object
The Number object is an object wrapper for primitive numeric values.
Syntax for creating a new Number object.
var myNum=new Number(number);
Properties
FF: Firefox, IE: Internet Explorer
Property
constructor
Description
Returns a reference to the Number function that created the
object
F
F
I
E
1
4
51
5 - javaScript
MAX_VALUE
Returns the largest possible value in JavaScript
1
4
MIN_VALUE
Returns the smallest possible value in JavaScript
1
4
NaN
Represents "Not-a-number" value
1
4
NEGATIVE_INFINIT
Represents a value that is less than MIN_VALUE
1
4
POSITIVE_INFINITY
Represents a value that is greater than MAX_VALUE
1
4
prototype
Allows you to add properties and methods to the object
1
4
Y
Methods
Method
Description
F
F
toExponential()
Converts the value of the object into an exponential notation
I
E
1
5
.5
toFixed()
Formats a number to the specified number of decimals
1
5
.5
toLocaleString()
toPrecision()
Converts a number into an exponential notation if it has
more digits than specified
1
5
.5
toString()
Converts the Number object into a string
1
4
valueOf()
Returns the value of the Number object
1
4
5.11.5 the Boolean object
The JavaScript Boolean object is an object wrapper for a Boolean value.
Properties
FF: Firefox, N: Netscape, IE: Internet Explorer
Property
constructor
prototype
Description
F
F
Returns a reference to the Boolean function that created the
object
Allows you to add properties and methods to the object
N
I
E
1
2
4
1
2
4
F
N
Methods
Method
Description
F
I
E
toSource()
Returns the source code of the object
1
4
-
toString()
Converts a Boolean value to a string and returns the result
1
4
4
valueOf()
Returns the primitive value of a Boolean object
1
4
4
52
5 - javaScript
5.11.6 the Math Object
The JavaScript Math object allows you to perform common mathematical tasks. It includes
several mathematical constants and functions.
Properties
FF: Firefox, N: Netscape, IE: Internet Explorer
F
Description
E
Returns Euler's constant (approx. 2.718)
1
2 3
LN2
Returns the natural logarithm of 2 (approx. 0.693)
1
2 3
LN10
Returns the natural logarithm of 10 (approx. 2.302)
1
2 3
LOG2E
Returns the base-2 logarithm of E (approx. 1.442)
1
2 3
LOG10E
Returns the base-10 logarithm of E (approx. 0.434)
1
2 3
PI
Returns PI (approx. 3.14159)
1
2 3
SQRT1_2
Returns the square root of 1/2 (approx. 0.707)
1
2 3
SQRT2
Returns the square root of 2 (approx. 1.414)
1
2 3
F
N I
E
F
N
E
I
Property
Methods
Method
Description
F
abs(x)
Returns the absolute value of a number
1
2 3
acos(x)
Returns the arccosine of a number
1
2 3
asin(x)
Returns the arcsine of a number
1
2 3
atan(x)
Returns the arctangent of x as a numeric value between -PI/2
and PI/2 radians
1
2 3
atan2(y,x)
Returns the angle theta of an (x,y) point as a numeric value
between -PI and PI radians
1
2 3
ceil(x)
Returns the value of a number rounded upwards to the nearest
integer
1
2 3
1
2 3
1
2 3
1
2 3
cos(x)
exp(x)
floor(x)
Returns the cosine of a number
Returns the value of
Ex
Returns the value of a number rounded downwards to the
nearest integer
log(x)
Returns the natural logarithm (base E) of a number
1
2 3
max(x,y)
Returns the number with the highest value of x and y
1
2 3
min(x,y)
Returns the number with the lowest value of x and y
1
2 3
pow(x,y)
Returns the value of x to the power of y
1
2 3
random()
Returns a random number between 0 and 1
1
2 3
round(x)
Rounds a number to the nearest integer
1
2 3
sin(x)
Returns the sine of a number
1
2 3
sqrt(x)
Returns the square root of a number
1
2 3
tan(x)
Returns the tangent of an angle
1
2 3
53
5 - javaScript
toSource()
Represents the source code of an object
1
4 -
valueOf()
Returns the primitive value of a Math object
1
2 4
5.12 how to create your own objects
An object is just a special kind of data, with a collection of properties and methods.
Let's illustrate with an example: A person is an object. Properties are the values associated with
the object. The persons' properties include name, height, weight, age, skin tone, eye color, etc. All
persons have these properties, but the values of those properties will differ from person to person.
Objects also have methods. Methods are the actions that can be performed on objects. The
persons' methods could be eat(), sleep(), work(), play(), etc.
5.12.1 Properties
The syntax for accessing a property of an object is:
objName.propName
You can add properties to an object by simply giving it a value. Assume that the personObj
already exists - you can give it properties named firstname, lastname, age, and eyecolor as
follows:
personObj.firstname="John";
personObj.lastname="Doe";
personObj.age=30;
personObj.eyecolor="blue";
document.write(personObj.firstname);
The code above will generate the following output:
John
5.12.2 Methods
An object can also contain methods.
You can call a method with the following syntax:
objName.methodName()
There are different ways to create a new object:
5.12.3 create a direct instance of an object
The following code creates an instance of an object and adds four properties to it:
personObj=new Object();
personObj.firstname="John";
personObj.lastname="Doe";
personObj.age=50;
personObj.eyecolor="blue";
54
5 - javaScript
Adding a method to the personObj is also simple. The following code adds a method called
eat() to the personObj:
personObj.eat=eat;
5.12.4 create a template of an object
The template defines the structure of an object:
function person(firstname,lastname,age,eyecolor)
{
this.firstname=firstname;
this.lastname=lastname;
this.age=age;
this.eyecolor=eyecolor;
}
Notice that the template is just a function. Inside the function you need to assign things to
this.propertyName. The reason for all the "this" stuff is that you're going to have more than one
person at a time (which person you're dealing with must be clear). That's what "this" is: the
instance of the object at hand.
Once you have the template, you can create new instances of the object, like this:
myFather=new person("John","Doe",50,"blue");
myMother=new person("Sally","Rally",48,"green");
You can also add some methods to the person object. This is also done inside the template:
function person(firstname,lastname,age,eyecolor)
{
this.firstname=firstname;
this.lastname=lastname;
this.age=age;
this.eyecolor=eyecolor;
this.newlastname=newlastname;
}
Note that methods are just functions attached to objects. Then we will have to write the
newlastname() function:
function newlastname(new_lastname)
{
this.lastname=new_lastname;
55
5 - javaScript
}
The newlastname() function defines the person's new last name and assigns that to the person.
JavaScript knows which person you're talking about by using "this.". So, now you can write:
myMother.newlastname("Doe").
5.13 JavaScript Events
New to HTML 4.0 was the ability to let HTML events trigger actions in the browser, like starting
a JavaScript when a user clicks on an HTML element.
Every element on a web page has certain events which can trigger JavaScript functions. For
example, we can use the onClick event of a button element to indicate that a function will run
when a user clicks on the button. We define the events in the HTML tags.
Examples of events:
●
A mouse click
●
A web page or an image loading
●
Mousing over a hot spot on the web page
●
Selecting an input box in an HTML form
●
Submitting an HTML form
●
A keystroke
Note: Events are normally used in combination with functions, and the function will not be
executed before the event occurs!
Tne following table contains an exhaustive list of events together with the support version of
FireFox, Netscape an Internet Explorer for each such event.
Event
The event occurs when...
F
N
F
I
E
onabort
Loading of an image is interrupted
1
3
4
onblur
An element loses focus
1
2
3
onchange
The user changes the content of a field
1
2
3
onclick
Mouse clicks an object
1
2
3
ondblclick
Mouse double-clicks an object
1
4
4
onerror
An error occurs when loading a document or an image
1
3
4
onfocus
An element gets focus
1
2
3
onkeydown
A keyboard key is pressed
1
4
3
onkeypress
A keyboard key is pressed or held down
1
4
3
onkeyup
A keyboard key is released
1
4
3
onload
A page or an image is finished loading
1
2
3
56
5 - javaScript
onmousedown
A mouse button is pressed
1
4
4
onmousemove
The mouse is moved
1
6
3
onmouseout
The mouse is moved off an element
1
4
4
onmouseover
The mouse is moved over an element
1
2
3
onmouseup
A mouse button is released
1
4
4
onreset
The reset button is clicked
1
3
4
onresize
A window or frame is resized
1
4
4
onselect
Text is selected
1
2
3
onsubmit
The submit button is clicked
1
2
3
onunload
The user exits the page
1
2
3
5.13.1 onload and onUnload
The onload and onUnload events are triggered when the user enters or leaves the page.
The onload event is often used to check the visitor's browser type and browser version, and load
the proper version of the web page based on the information.
Both the onload and onUnload events are also often used to deal with cookies that should be
set when a user enters or leaves a page. For example, you could have a popup asking for the
user's name upon his first arrival to your page. The name is then stored in a cookie. Next time the
visitor arrives at your page, you could have another popup saying something like: "Welcome John
Doe!".
5.13.2 onFocus, onBlur and onChange
The onFocus, onBlur and onChange events are often used in combination with validation of
form fields.
Below is an example of how to use the onChange event. The checkEmail() function will be
called whenever the user changes the content of the field:
<input type="text" size="30" id="email" onchange="checkEmail()">;
5.13.3 onSubmit
The onSubmit event is used to validate ALL form fields before submitting it.
Below is an example of how to use the onSubmit event. The checkForm() function will be called
when the user clicks the submit button in the form. If the field values are not accepted, the submit
should be cancelled. The function checkForm() returns either true or false. If it returns true the
form will be submitted, otherwise the submit will be cancelled:
<form method="post" action="xxx.htm" onsubmit="return checkForm()">
5.13.4 onMouseOver and onMouseOut
onMouseOver and onMouseOut are often used to create "animated" buttons.
Below is an example of an onMouseOver event. An alert box appears when an onMouseOver
event is detected:
<a href="http://www.w3schools.com" onmouseover="alert('An onMouseOver
57
5 - javaScript
event');return false">
<img src="w3schools.gif" width="100" height="30"> </a>
58
6 - Html DOM
6 - HTML DOM
6.1 what is the DOM?
The W3C Document Object Model (DOM) is a platform and language-neutral interface that
allows programs and scripts to dynamically access and update the content, structure, and style of
a document.
The W3C DOM provides a standard set of objects for HTML and XML documents, and a
standard interface for accessing and manipulating them.
The W3C DOM is separated into different parts (Core, XML, and HTML) and different levels
(DOM Level 1/2/3):
•
•
•
Core DOM - defines a standard set of objects for any structured document
XML DOM - defines a standard set of objects for XML documents
HTML DOM - defines a standard set of objects for HTML documents
A web browser is not obliged to use DOM in order to render an HTML document. However, the
DOM is required by JavaScript scripts that wish to inspect or modify a web page dynamically. In
other words, the Document Object Model is the way JavaScript sees its containing HTML page
and browser state.
Because the DOM supports navigation in any direction (e.g., parent and previous sibling) and
allows for arbitrary modifications, an implementation must at least buffer the document that has
been read so far (or some parsed form of it). Hence the DOM is likely to be best suited for
applications where the document must be accessed repeatedly or out of sequence order. If the
application is strictly sequential and one-pass, the SAX model is likely to be faster and use less
memory. SAX (Simple API for XML) is a sequential access parser API for XML. SAX provides a
mechanism for reading data from an XML document. It is a popular alternative to the Document
Object Model (DOM).
6.2 history
The World Wide Web Consortium (W3C) developed the W3C Document Object Model in
response to the development of various proprietary models for HTML, particularly those used in
Web browsers. The existing vendor-specific interfaces were dubbed intermediate DOMs.
W3C began development of the DOM in the mid-1990s. Although the W3C never produced a
specification for DOM 0, it was nonetheless a partially documented model and was included in the
specification of HTML 4. By October 1998, the first specification of DOM (DOM 1) was released.
DOM 2 was issued in November 2000, with specifics on the style sheet object model and style
information manipulation. DOM 3 was released in April 2004 and is the current release of the
DOM specification.
As of January 2008, the Document Object Model activity is closed. The Document Object
Model Working Group was closed in the Spring of 2004, after the completion of the DOM Level 3
Recommendations. Several W3C Working Groups have since taken the lead in maintaining and
continuing to develop standard APIs for the Web since then; HTML, SVG, CSS, or WebAPI being
among them.
Right now (oct. 2010), what drives the DOM Specifications is the WebApps WG. The W3C
59
6 - Html DOM
Web Applications Working Group has taken over responsibility for the Document Object Model
specifications, including a new revision of DOM Level 3 Events, a new DOM Core specification,
and potentially any errata on older DOM specifications.
6.3 levels
The W3C DOM specifications are divided into levels, each of which contains required and
optional modules. To claim to support a level, an application must implement all the requirements
of the claimed level and the levels below it. An application may also support vendor-specific
extensions which don't conflict with the W3C standards. As of 2005, Level 1, Level 2, and some
modules of Level 3 are W3C Recommendations which means they have reached their final form.
Level 0
The application supports an intermediate DOM, which existed before the creation of DOM Level
1. Examples include the DHTML Object Model or the Netscape intermediate DOM. Level 0 is not
a formal specification published by the W3C but rather a shorthand that refers to what existed
before the standardization process.
Level 1
Navigation of DOM (HTML and XML) document (tree structure) and content manipulation
(includes adding elements). HTML-specific elements are included as well.
Level 2
XML namespace support, filtered views and events.
Level 3
Consists of 6 different specifications:
1. DOM Level 3 Core;
2. DOM Level 3 Load and Save;
3. DOM Level 3 XPath;
4. DOM Level 3 Views and Formatting;
5. DOM Level 3 Requirements; and
6. DOM Level 3 Validation, which further enhances the DOM
6.4 specifications
•
•
•
Document Object Model (DOM) Level 1 Specification
Level 2 Recommendations:
• Document Object Model (DOM) Level 2 Core Specification
• Document Object Model (DOM) Level 2 Views Specification
• Document Object Model (DOM) Level 2 Events Specification
• Document Object Model (DOM) Level 2 Style Specification
• Document Object Model (DOM) Level 2 Traversal and Range Specification
• Document Object Model (DOM) Level 2 HTML Specification
Level 3 Recommendations:
• Document Object Model (DOM) Level 3 Core Specification
60
6 - Html DOM
Document Object Model (DOM)
Document Object Model (DOM)
Level 3 Working Group Notes:
• Document Object Model (DOM)
• Document Object Model (DOM)
• Document Object Model (DOM)
Working Draft
• Window Object 1.0
•
•
•
•
Level 3 Load and Save Specification
Level 3 Validation Specification
Level 3 XPath Specification
Level 3 Views and Formatting Specification
Requirements
6.5 web browsers implementation
Earlier, when each Web browser exclusively supported its own intermediate DOM,
interoperability problems were numerous. In order to be cross-browser compatible, that is, support
multiple browsers, large parts of Dynamic HTML code had to be rewritten for each browser to be
supported. A common DOM promised substantial simplification of the development of complex
Web applications.
W3C DOM Level 1 has been a recommendation since 1 October 1998. The standardization
effort did not bring forth an immediate change, because non-conformant browsers such as
Internet Explorer 4.x and Netscape 4.x were still widely used in 2000. By 2005, large parts of
W3C DOM were well-supported by common JavaScript-enabled Web browsers, including
Microsoft Internet Explorer (version 5 (1999) and version 6 (2001)), Gecko-based browsers (like
Mozilla and Firefox), Opera, Konqueror, and Safari. Web developers are starting to rely mostly or
solely on W3C DOM, since it allows browser compatibility with a large audience.
6.6 javaScript specific objects
In addition to the built-in JavaScript objects, you can also access and manipulate all of the
HTML DOM objects with JavaScript. Besides the generic objects listed bellow, the bulk of the
HTML DOM objects are presented in the next paragraph.
Object
Window
Description
The top level object in the JavaScript hierarchy. The Window object
represents a browser window. A Window object is created automatically
with every instance of a <body> or <frameset> tag
Navigator
Contains information about the client's browser
Screen
Contains information about the client's display screen
History
Contains the visited URLs in the browser window
Location
Contains information about the current URL
6.7 the HTML DOM
The HTML DOM defines a standard set of objects for HTML, and a standard way to access and
manipulate HTML documents.
All HTML elements, along with their containing text and attributes, can be accessed through the
61
6 - Html DOM
DOM. The contents can be modified or deleted, and new elements can be created.
The HTML DOM is platform and language independent. It can be used by any programming
language like Java, JavaScript, and VBScript.
HTML DOM Objects
Object
Document
Description
Represents the entire HTML document and can be used to access all
elements in a page
Anchor
Represents an <a> element
Area
Represents an <area> element inside an image-map
Base
Represents a <base> element (specifies a default address or a default
target for all links on a page)
Body
Represents the <body> element
Button
Represents a <button> element
Event
Represents the state of an event
Form
Represents a <form> element
Frame
Represents a <frame> element
Frameset
Represents a <frameset> element
Iframe
Represents an <iframe> element
Image
Represents an <img> element
Input button
Represents a button in an HTML form
Input checkbox
Represents a checkbox in an HTML form
Input file
Represents a fileupload in an HTML form
Input hidden
Represents a hidden field in an HTML form
Input password
Represents a password field in an HTML form
Input radio
Represents a radio button in an HTML form
Input reset
Represents a reset button in an HTML form
Input submit
Represents a submit button in an HTML form
Input text
Represents a text-input field in an HTML form
Link
Represents a <link> element
Meta
Represents a <meta> element
Option
Represents an <option> element
Select
Represents a selection list in an HTML form
Style
Represents an individual style statement
Table
Represents a <table> element
TableData
Represents a <td> element
TableRow
Represents a <tr> element
Textarea
Represents a <textarea> element
62
6 - Html DOM
6.8 DOM nodes
According to the DOM, everything in an HTML document is a node.
The DOM says:
•
•
•
•
•
The entire document is a document node
Every HTML tag is an element node
The text in the HTML elements are text nodes
Every HTML attribute is an attribute node
Comments are comment nodes
6.8.1 DOM example
Look at the following HTML document:
<html>
<head>
<title>DOM Tutorial</title>
</head>
<body>
<h1>DOM Lesson one</h1>
<p>Hello world!</p>
</body>
</html>
The root node in the HTML above is <html>. All other nodes in the document are contained
within <html>.
The <html> node has two child nodes; <head> and <body>.
The <head> node holds a <title> node. The <body> node holds a <h1> and <p> node.
6.8.2 text is always stored in text nodes
A common error in DOM processing is to expect an element node to contain text.
However, the text of an element node is stored in a text node.
In this example: <title>DOM Tutorial</title>, the element node <title>, holds a text node with
the value "DOM Tutorial".
"DOM Tutorial" is not the value of the <title> element!
However, in the HTML DOM the value of the text node can be accessed by the innerHTML
property.
6.9 the HTML DOM Node Tree
6.9.1 the Document Tree
The HTML DOM views a HTML document as a tree-structure. The tree structure is called a
node-tree.
63
6 - Html DOM
All nodes can be accessed through the tree. Their contents can be modified or deleted, and new
elements can be created.
The node tree below shows the set of nodes, and the connections between them. The tree
starts at the root node and branches out to the text nodes at the lowest level of the tree:
6.9.2 node parents, children, and siblings
The nodes in the node tree have a hierarchical relationship to each other.
The terms parent, child, and sibling are used to describe the relationships. Parent nodes have
children. Children on the same level are called siblings (brothers or sisters).
•
•
•
•
•
In a node tree, the top node is called the root
Every node, except the root, has exactly one parent node
A node can have any number of children
A leaf is a node with no children
Siblings are nodes with the same parent
6.9.3 accessing nodes
You can access a node in three ways:
1. By using the getElementById() method
2. By using the getElementsByTagName() method
3. By navigating the node tree, using the node relationships.
The following example returns a nodeList of all <p> elements that are descendants of the
element with id="main":
document.getElementById('main').getElementsByTagName("p");
The length property defines the length of a node list (the number of nodes). You can loop
through a node list by using the length property:
x=document.getElementsByTagName("p");
64
6 - Html DOM
for (i=0;i<x.length;i++)
{
document.write(x[i].innerHTML);
document.write("<br />");
}
6.9.4 Node Properties
In the HTML Document Object Model (DOM), each node is an object.
Objects have methods (functions) and properties (information about the object), that can be
accessed and manipulated by JavaScript.
Three important HTML DOM node properties are:
•
nodeName
•
nodeValue
•
nodeType
the nodeName Property
The nodeName property specifies the name of a node.
•
nodeName is read-only
•
nodeName of an element node is the same as the tag name
•
nodeName of an attribute node is the attribute name
•
nodeName of a text node is always #text
•
nodeName of the document node is always #document
the nodeValue Property
The nodeValue property specifies the value of a node.
•
nodeValue for element nodes is undefined
•
nodeValue for text nodes is the text itself
•
nodeValue for attribute nodes is the attribute value
the nodeType Property
The nodeType property returns the type of node and is read only. The most important node
types are:
Element type
NodeType
Element
1
Attribute
2
Text
3
Comment
8
Document
9
65
6 - Html DOM
6.9.5 example - get the value of an element
The following code fragment retrieves the text node value of the first <p> element:
x=document.getElementById("intro").firstChild;
txt=x.nodeValue;
6.10 HTML events
Common/W3C events
There is a huge collection of events that can be generated by most element nodes:
•
•
•
•
•
•
Mouse events
Keyboard events
HTML frame/object events
HTML form events
User interface events
Mutation events (notification of any changes to the structure of a document)
Note that the event classification above is not exactly the same as W3C's classification.
Category
Type
Attribute
Description
click
onclick
Fires when the pointing device
button is clicked over an element.
A click is defined as a mousedown
and mouseup over the same
screen location. The sequence of
these events is:
• mousedown
• mouseup
• click
dblclick
ondblclick
Fires when the pointing device
button is double clicked over an
element
mousedown
onmousedown
Fires when the pointing device
button is pressed over an element
mouseup
onmouseup
Fires when the pointing device
button is released over an element
mouseover
onmouseover
Fires when the pointing device
is moved onto an element
mousemove
onmousemove
Fires when the pointing device
is moved while it is over an
element
mouseout
onmouseout
Fires when the pointing device
is moved away from an element
Mouse
66
6 - Html DOM
keypress
onkeypress
Fires when a key on the
keyboard is "clicked". A keypress
is defined as a keydown and keyup
on the same key. The sequence of
these events is:
• keydown
• keyup
• keypress
keydown
onkeydown
Fires when a key on the
keyboard is pressed
keyup
onkeyup
Fires when a key on the
keyboard is released
onload
Fires when the user agent
finishes loading all content within a
document, including window,
frames, objects and images.
For elements, it fires when the
target element and all of its
content has finished loading
unload
onunload
Fires when the user agent
removes all content from a window
or frame. For elements, it fires
when the target element or any of
its content has been removed
abort
onabort
Fires when an object/image is
stopped from loading before
completely loaded
error
onerror
Fires when an
object/image/frame cannot be
loaded properly
resize
onresize
Fires when a document view is
resized
scroll
onscroll
Fires when a document view is
scrolled
select
onselect
Fires when a user selects some
text in a text field, including input
and textarea
change
onchange
Fires when a control loses the
input focus and its value has been
modified since gaining focus
submit
onsubmit
Fires when a form is submitted
reset
onreset
Fires when a form is reset
focus
onfocus
Fires when an element receives
focus either via the pointing device
or by tab navigation
blur
onblur
Fires when an element loses
focus either via the pointing device
or by tabbing navigation
DOMFocusIn
ondomfocusin
Keyboard
load
HTML
frame/object
HTML
form
User
interface
Similar to HTML focus event,
but can be applied to any
focusable element
67
6 - Html DOM
ondomfocusout
Similar to HTML blur event, but
can be applied to any focusable
element
DOMActivate
ondomactivate
Similar to XUL command event.
Fires when an element is
activated, for instance, through a
mouse click or a keypress.
DOMSubtreeModified
onsubtreemodified
Fire when the subtree is
modified
DOMNodeInserted
onnodeinserted
Fires when a node has been
added as a child of another node
DOMNodeRemoved
onnoderemoved
Fires when a node has been
removed from a DOM-tree
DOMFocusOut
Mutation
NodeInsertedIntoDoc
onnodeinsertedinto
Fires when a node is being
ument
document
inserted into a document
DOMAttrModified
onattrmodified
Fires when an attribute has been
modified
DOMCharacterDataM
oncharacterdatamo
Fires when the character data
odified
dified
has been modified
Note that the events whose names start with “DOM” are currently not well supported. Mozilla
and Opera support DOMAttrModified, DOMNodeInserted, DOMNodeRemoved and
DOMCharacterDataModified. Safari, as of version 1.3, also supports these methods.
Also, Mozilla, Safari and Opera also support readystatechange event for the XMLHttpRequest
object. Mozilla also supports the beforeunload event using traditional event registration method
(DOM Level 0). Mozilla and Safari also support contextmenu, but Internet Explorer for the Mac
does not.
6.11 event flow
Consider the situation when there are 2 elements nested together. Both have event handlers
registered on the same event type, say "click". When the user clicks on the inner element, there
are two possible ways to handle it:
•
Trigger the elements from outer to inner (event capturing). This model is implemented in
Netscape Navigator.
•
Trigger the elements from inner to outer (event bubbling). This model is implemented in
Internet Explorer and other browsers.
W3C takes a middle position in this struggle. Events are first captured until it reaches the target
element, and then bubbled up. During the event flow, an event can be responded to at any
element in the path (an observer) in either phase by causing an action, and/or by stopping the
event (with method event.stopPropagation() for Mozilla and command
event.cancelBubble = true for Internet Explorer), and/or by cancelling the default action for
the event.
68
6 - Html DOM
6.12 the Event object
The Event object provides a lot of information about a particular event, including information
about target element, key pressed, mouse button pressed, mouse position, etc. Unfortunately,
there are very serious browser incompatibilities in this area. Hence only the W3C Event object is
discussed here.
Event properties
Type
Name
Description
DOMString
type
The name of the event (case-insensitive).
EventTarget
target
Used to indicate the EventTarget to which the event was
originally dispatched.
EventTarget
currentTarget
Used to indicate the EventTarget whose EventListeners
are currently being processed.
unsigned short
eventPhase
Used to indicate which phase of event flow is currently
being evaluated.
boolean
bubbles
Used to indicate whether or not an event is a bubbling
event.
boolean
cancelable
Used to indicate whether or not an event can have its
default action prevented.
DOMTimeStamp
timeStamp
Used to specify the time (in milliseconds relative to the
epoch) at which the event was created.
Event methods
Name
Argument
type
Argument
name
Description
stopPropagation
To prevent further propagation of an
event during event flow.
preventDefault
To cancel the event if it is cancelable,
meaning that any default action normally
taken by the implementation as a result of
the event will not occur.
initEvent
DOMString
eventTypeArg
Specifies the event type.
boolean
canBubbleArg
Specifies whether or not the event can
bubble.
boolean
cancelableArg
Specifies whether or not the event's
default action can be prevented.
69
7 - AJAX
7 - AJAX
7.1 what is ajax?
Ajax stands for Asynchronous JavaScript And XML. It is not a technology in itself, but rather a
collection of existing technologies bound together by JavaScript.
•
•
•
HTML and CSS for presenting.
JavaScript (ECMAScript) for local processing, and DOM (Document Object Model) to
access data inside the page or to access elements of Xml file read on the server (with the
getElementByTagName method for example)
The XMLHttpRequest class read or send data on the server asynchronously.
optionally
•
•
•
•
The DomParser class may be used
PHP or another scripting language may be used on the server.
XML and XSLT to process the data if returned in Xml form.
SOAP may be used to dialog with the server.
XSL stands for EXtensible Stylesheet Language while XSLT stands for XSL Transformations
The "Asynchronous" word, means that the response of the server will be processed when
available, without to wait and to freeze the display of the page.
7.2 why use ajax?
Mainly to build a fast, dynamic website, but also to save resources. For improving sharing of
resources, it is better to use the power of all the client computers rather than just an unique server
and network. Ajax allows to perform processing on client computer (in JavaScript) with data taken
from the server.
The processing of web page formerly was only server-side, using web services or Php scripts,
before the whole page was sent within the network.
But Ajax can selectively modify a part of a page displayed by the browser, and update it without
the need to reload the whole document with all images, menus, etc.
For example, fields of forms, choices of user, may be processed and the result displayed
immediately into the same page.
7.3 the basic architecture of ajax
The classic web application model works like this: most user actions in the interface trigger an
HTTP request back to a web server. The server does some processing — retrieving data,
crunching numbers, talking to various legacy systems — and then returns an HTML page to the
client. It’s a model adapted from the Web’s original use as a hypertext medium, but what makes
70
7 - AJAX
the Web good for hypertext doesn’t necessarily make it good for software applications.
The traditional model for web applications (left) compared to the Ajax model (right)
This approach makes a lot of technical sense, but it doesn’t make for a great user experience.
While the server is doing its thing, what’s the user doing? That’s right, waiting. And at every step
in a task, the user waits some more.
Obviously, if we were designing the Web from scratch for applications, we wouldn’t make users
wait around. Once an interface is loaded, why should the user interaction come to a halt every
time the application needs something from the server? In fact, why should the user see the
application go to the server at all?
An Ajax application eliminates the start-stop-start-stop nature of interaction on the Web by
introducing an intermediary — an Ajax engine — between the user and the server. It seems like
adding a layer to the application would make it less responsive, but the opposite is true.
Instead of loading a web page, at the start of the session, the browser loads an Ajax engine —
written in JavaScript and usually tucked away in a hidden frame. This engine is responsible for
both rendering the interface the user sees and communicating with the server on the user’s
behalf. The Ajax engine allows the user’s interaction with the application to happen
asynchronously — independent of communication with the server. So the user is never staring at
a blank browser window and an hourglass icon, waiting around for the server to do something.
71
7 - AJAX
The synchronous interaction pattern of a traditional web application (top) compared with the
asynchronous pattern of an Ajax application (bottom)
Every user action that normally would generate an HTTP request takes the form of a JavaScript
call to the Ajax engine instead. Any response to a user action that doesn’t require a trip back to
the server — such as simple data validation, editing data in memory, and even some navigation
— the engine handles on its own. If the engine needs something from the server in order to
respond — if it’s submitting data for processing, loading additional interface code, or retrieving
new data — the engine makes those requests asynchronously, usually using XML, without stalling
a user’s interaction with the application.
72
7 - AJAX
7.4 how does it work?
Ajax uses a programming model with display and events. These events are user actions, they
call functions associated to elements of the web page.
Interactivity is achieved with forms and buttons. DOM allows to link elements of the page with
actions and also to extract data from Xml files provided by the server.
To get data on the server, the ajax engine uses the XMLHttpRequest object. This object
provides two methods:
- open: create a connection.
- send: send a request to the server.
Data furnished by the server will be found in these attributes of the XMLHttpRequest object:
- responseXml - for a Xml file or
- responseText - for a simple text.
Take note that a new XMLHttpRequest object has to be created for each new file to load.
We have to wait for the data to be available to process it, and in this purpose, the state of
availability of data is given by the readyState attribute of XMLHttpRequest.
States of readyState follow (only the last one is really useful):
0: not initialized.
1: connection established.
2: request received.
3: answer in process.
4: finished.
7.5 the XMLHttpRequest class
Here is a closer look to the XMLHttpRequest class. It allows the interaction with the servers,
thanks to its methods and attributes.
Attributes
readyState
- the code successively changes value from 0 to 4 that means "ready".
status
- returned by the server - 200 is ok, 404 if the page is not found
responseText
- holds loaded data as a string of characters.
responseXml
- holds a Xml loaded file, DOM's method allows to extract data.
onreadystatechange - the name of the function invoked
Methods
open(mode, url, boolean)
- mode: type of request, GET or POST
- url: the location of the file
73
7 - AJAX
- boolean: true (asynchronous) / false (synchronous)
send("string")
- null for a GET command
7.6 building a request, step by step
First step: create an instance
This is just a classical instance of class, but two options must be tried, for browser compatibility.
if (window.XMLHttpRequest) // Object of the current windows
{
request = new XMLHttpRequest();
// Firefox, Safari, ...
}
else if (window.ActiveXObject)
// ActiveX version
{
request = new ActiveXObject("Microsoft.XMLHTTP");
// IE
}
Second step: wait for the response
The response and further processing are included in a function and the return of the function
will be assigned to the onreadystatechange attribute of the object previously created.
request.onreadystatechange = function()
{ // instructions to process the response };
if (request.readyState == 4)
{
// received, OK
}
else
{
// wait...
}
Third step: make the request itself
Two methods of XMLHttpRequest are used:
- open: command GET or POST, URL of the document, true for asynchronous.
- send: with POST only, the data to send to the server.
The request below reads a document on the server.
http_request.open('GET', 'http://www.xul.fr/somefile.xml', true);
http_request.send(null);
74
7 - AJAX
7.7 examples
7.7.1 How to get a text
<html>
<head>
<script>
function submitForm()
{
var req = null;
if(window.XMLHttpRequest) req = new XMLHttpRequest();
else if (window.ActiveXObject)
req = new ActiveXObject(Microsoft.XMLHTTP);
req.onreadystatechange = function()
{
if(req.readyState == 4)
if(req.status == 200)
document.ajax.dyn="Received:" + req.responseText;
else
document.ajax.dyn="Error code " + req.status;
};
req.open("GET", "data.xml", true);
req.setRequestHeader("Content-Type",
"application/x-www-form-urlencoded");
req.send(null);
}
</script>
</head>
<body>
<FORM method="POST" name="ajax" action="">
<INPUT type="BUTTON" value="Submit" ONCLICK="submitForm()">
<INPUT type="text" name="dyn" value="">
</FORM>
</body>
</html>
7.7.2 how to get from xml
To get data from a xml file we have just to replace this line:
document.ajax.dyn=""Received:" + req.responseText;
by this code:
var doc = req.responseXML; // assign the Xml file to a var
var element = doc.getElementsByTagName('root').item(0);
// read the
first element with a dom's method
75
7 - AJAX
document.ajax.dyn.value= element.firstChild.data;
content of the element to the form
// assign the
7.7.3 how to post a text
A text is sent to the server and is written into a file. The call to the "open" method changes, the
argument is POST, and the "send" method also has now a value for argument.
req.open("POST", "ajax-post.xml", true);
req.setRequestHeader("Content-Type",
"application/x-www-form-urlencoded");
req.send(document.getElementById("dyn".value));
7.7.4 how to write to body
Now, the text read is put in the body of the page, and not into a textfield. The code below
replaces the textfield form object and the second part replaces the assignment into the JavaScript
function.
<div id="zone">
... some text to replace ...
</div>
document.getElementById("zone").innerHTML = "Received:" +
xhr.responseText;
7.8 the ajax toolkit framework
It is an Eclipse add-on that provides tools for building IDE for Ajax runtimes, and testing Ajax
applications. The AJAX Toolkit Framework (ATF) provides and extensible framework and
exemplary tools for building IDEs for the many different AJAX runtime offerings (Dojo, Zimbra,
Rico, etc) in the market. Tools built upon these frameworks will initially include: enhanced
JavaScript editing features such as edit-time syntax checking; an embedded Mozilla web browser;
an embedded DOM browser; and an embedded JavaScript debugger.
7.9 drawbacks of ajax
●
If JavaScript is not activated, Ajax can't work. The user must be asked to set JavaScript
from within options of the browser, with the "noscript" tag.
●
Since data to display are loaded dynamically, they are not part of the page, and the
keywords inside are not used by search engines.
●
The asynchronous mode may change the page with delays (when the processing on the
server take some times), this may be disturbing.
●
The back button may be deactivated (this is not the case in examples provided here).
76
7 - AJAX
7.10 Specifications
Ajax is based on these specifications:
●
XML 1, HTML 4.0, DOM 2, from W3C
●
ECMAScript 1.5 (standard for JavaScript) from ECMA
●
W3C draft specification for XMLHttpRequest.
77
8 - WEB APPLICATIONS
8 - WEB APPLICATIONS
8.1 the structure of a web application
A web application is a collection of Java servlets, JSP pages, Java Server Faces, other helper
classes and class libraries, other static resources (HTML, images, etc.) and an xml file, the
deployment descriptor.
A web application consists of 4 parts:
1. a public directory – containing html, jsp files and other public resources. This is the root
directory of the application.
2. a WEB-INF/web.xml file – the deployment descriptor.
3. a WEB-INF/classes directory.
4. a WEB-INF/lib directory.
Example:
Assume that we use a Tomcat web server and that the environment variable
%TOMCAT_HOME% is set to C:\TW\Tomcat. Then, the root directory of some web application
can be:
C:\TW\Tomcat\webapps\bank11\ccards
and the mandatory directories are:
C:\TW\Tomcat\webapps\bank11\ccards\WEB-INF\classes
C:\TW\Tomcat\webapps\bank11\ccards\WEB-INF\lib
8.2 web containers
A web container is a Java runtime providing implementation of the Java servlet API and some
other facilities to the JSP and JSF pages. It responsible for initializing, invoking and managing the
life cycle of servlets, JSPs and JSFs.
A web container may either implement the basic HTTP services or delegates these services to
an external web server.
Web containers can be part of an application or web server or a separate runtime. Here is a
description of these situations.
•
web container in a J2EE application server. Commercial implementations of the J2EE
specifications, like WebLogic, Inprise Application Server or IBM's WebSphere include
web containers.
•
web container built into web servers. Most known cases are the Sun's (Oracle's) Java
WebServer and the Jakarta Tomcat web server.
•
web container as a separate runtime. Some web servers, like Apache or IIS require a
separate runtime to run servlets and a web server plug-in to integrate this Java runtime
78
8 - WEB APPLICATIONS
with the web server. Typical integration scenarios are Tomcat with Apache and JRun (of
Allaire) with most of the J2EE application servers.
Web Application
Java Servlets
Web Application
Java Servlets
JSP Pages
JSP Pages
JavaServer
Faces
JavaServer
Faces
Java
Classes
Deployment descriptor
Deployment descriptor
Java EE Web Container
8.3 container services
Containers are the interface between a component and the low-level platform-specific
functionality that supports the component. Before a web, enterprise bean, or application client
component can be executed, it must be assembled into a Java EE module and deployed into its
container.
The assembly process involves specifying container settings for each component in the Java
EE application and for the Java EE application itself. Container settings customize the underlying
support provided by the Java EE server, including services such as security, transaction
management, Java Naming and Directory Interface (JNDI) lookups, and remote connectivity.
Here are some of the highlights:
•
The Java EE security model lets you configure a web component or enterprise bean so
that system resources are accessed only by authorized users.
79
8 - WEB APPLICATIONS
•
The Java EE transaction model lets you specify relationships among methods that make
up a single transaction so that all methods in one transaction are treated as a single unit.
•
JNDI lookup services provide a unified interface to multiple naming and directory
services in the enterprise so that application components can access these services.
•
The Java EE remote connectivity model manages low-level communications between
clients and enterprise beans. After an enterprise bean is created, a client invokes
methods on it as if it were in the same virtual machine.
Because the Java EE architecture provides configurable services, application components
within the same Java EE application can behave differently based on where they are deployed.
For example, an enterprise bean can have security settings that allow it a certain level of access
to database data in one production environment and another level of database access in another
production environment.
The container also manages nonconfigurable services such as enterprise bean and servlet life
cycles, database connection resource pooling, data persistence, and access to the Java EE
platform APIs.
8.4 deployment descriptor
The deployment descriptor is an xml file (namely, web.xml) which allows the customization of
the web application at deployment time.
The deployment descriptor serves several purposes, like:
1. Initialization of parameters for servlets, JSPs and Java Server Faces.
2. Servlet, JSPs and Java Server Faces definitions, servlet classes, precompiled JSP
entities are declared (names, classes, descriptions).
3. Servlet, JSPs and Java Server Faces mappings.
4. MIME types used by the web application.
5. Security related entries – may specify which pages require login and the roles different
users may have.
6. Others, like what pages are error, welcome pages, entries related to session
configuration.
Here is a small, but typical web.xml file:
<?xml version="1.0" encoding="ISO-8859-1" ?>
<!DOCTYPE web-app (View Source for full doctype...)>
<web-app>
<!-- Define the Bank 11 ccards Servlets -->
<servlet>
<servlet-name>Login</servlet-name>
<servlet- class>com.bank11.ccards.servlets.LoginServlet
</servlet-class>
</servlet>
</web-app>
80
8 - WEB APPLICATIONS
8.5 practical deployment issues
There are several issues with the web applications deployment. Behind a very benign URL, like
"http://localhost:8080/ccards/servlet/Enroll" there are 3 things which have to be fixed in order to
make things work properly.
Assume that we work with Tomcat and that the environment variable %TOMCAT_HOME% (or
$TOMCAT_HOME, in an UNIX environment) is set to "C:\TW\Tomcat".
1. The "/servlet" part of the URL tells the web server (Tomcat, in our case) to execute the
invoker servlet. This association is made in the file "%TOMCAT_HOME%\conf\web.xml".
Unfortunately, the lines which deal with this issue are commented out in the latest version
of Tomcat (for so-called "security issues"). To make anything work:
•
de-comment the following section:
<servlet-mapping>
<servlet-name>invoker</servlet-name>
<url-pattern>/servlet/*</url-pattern>
</servlet-mapping>
in the configuration file "%TOMCAT_HOME%\conf\web.xml"
2. The "/ccards" part of the URL is, basicly, the name of the web application. In general, the
base directory of an application is a subdirectory of the "%TOMCAT_HOME%\webapps"
directory. This subdirectory has (in general) the same name as the application itself.
However, for flexibility, the location of the base directory of a web application may be any
sub(sub)directory of "%TOMCAT_HOME%\webapps". The association between the name
of the web application and the location of its base directory is made by a <context>
element in the "%TOMCAT_HOME%\conf\server.xml" file. For example, if the base
directory of the "/ccards" web application is "%TOMCAT_HOME
%\webapps\vdumitrascu\cc", then the corresponding <context> element in the
"%TOMCAT_HOME%\conf\server.xml" file looks like:
<context path="/ccards" docbase="vdumitrascu/cc" />
3. The "/Enroll" part of the URL identifies the servlet. Basicly, it is the alias of the real servlet
class, whose name is rather long. Let's say that this class is "EnrollServlet.class" and that it
is part of the package "com.bank11.ccards.servlets". Then the "EnrollServlet.class" file
must be located in the directory "%TOMCAT_HOME%\webapps\vdumitrascu\cc\WEBINF\classes\com.bank11.ccards.servlets". This association between the (short) alias of the
servlet and its real (long) name is made in the web.xml file of the web application. More
exactly the corresponding <servlet> element should look like:
<servlet>
<servlet-name>Enroll</servlet-name>
<servlet-class>com.bank11.ccards.servlets.EnrollServlet
</servlet-class>
</servlet>
81
9 - SERVLETS
9 - SERVLETS
9.1 the servlets as part of web applications
Java servlets – small, platform independent programs, which extend the functionality of the
web server.
Technically speaking, a servlet is a Java class that extends the GenericServlet (or, more often,
the HttpServlet) class.
The Java Servlet API provides a simple frame for building web applications on web servers.
The current Java Servlet specification is 2.5 and is in final state. Java EE 6 SDK is intended to
contain an implementation of the Java Servlet 3.0 specification, but at this point, this is just a
work in progress. As of oct. 2010, the Java Servlet 3.0 specification is available for public review.
9.2 servlet containers
The servlet does not communicate directly with the client, but through a web container. The
servlet lives within this container which provides an execution environment for the servlet class.
Web containers are implemented by various vendors, in most cases as part of an application
server.
9.2.1 Noncommercial servlet containers
Apache Tomcat (formerly Jakarta Tomcat) is an open source web container available
under the Apache Software License.
•
•
Apache Geronimo is a full Java EE implementation by Apache.
•
Jetty
•
Jaminid contains a higher abstraction than servlets.
•
Enhydra
•
Winstone supports specification 2.4, has a focus on minimal configuration and the ability
to strip the container down to only what you need.
•
tjws spec 2.4, small footprint, modular design
9.2.2 commercial servlet containers
•
BEA WebLogic Server or Weblogic Express, from BEA Systems, now bought by Oracle
•
Borland Enterprise Server
•
GlassFish (open source), maintained by Oracle
•
Java System Application Server , from Sun Microsystems (Oracle)
•
Java System Web Server , from Sun Microsystems (Oracle)
•
JBoss (open source)
•
JRun, from Adobe Systems (formerly developed by Allaire Corporation)
82
9 - SERVLETS
•
LiteWebServer (open source)
•
Oracle Application Server , from Oracle Corporation
•
Orion Application Server , from IronFlare
•
Caucho's Resin Server
•
ServletExec , from New Atlanta Communications
•
WebObjects, from Apple Inc.
•
WebSphere, from IBM
9.3 servlet packages and classes
The Java servlet API consists of 2 packages, which are part of the Java Platform SDK,
Enterprise Edition. These packages are:
•
javax.servlet
•
javax.servlet.http
The classes and interfaces defined in the javax.servlet package are protocol independent, while
the second one, the javax.servlet.http contains classes and interfaces which are HTTP specific.
The classes and interfaces of the Java servlet API can be divided in several categories,
namely:
•
servlet implementation
•
servlet configuration
•
servlet exceptions
•
request and responses
•
session tracking
•
servlet context
•
servlet collaboration
•
miscellaneous
9.4 the Servlet interface
The Servlet interface is part of the javax.servlet package. It declares the following
methods:
public void init(ServletConfig config)
throws ServletException;
public void service(ServletRequest req, ServletResponse resp) throws
ServletException, IOException;
public void destroy() throws ServletException;
public ServletConfig getServletConfig();
83
9 - SERVLETS
public String getServletInfo();
After instantiating the servlet, the web container calls its init() method. The method
performs all initialization required, before the servlet processes any HTTP request. The servlet
specification insures that the init() method is called just once for any given instance of the
servlet.
The web container calls the service() method in response to any incoming request. This
method has two arguments, arguments which implement the ServletRequest and
ServletResponse interfaces, respectively.
More on the servlet life cycle, in a different section.
9.5 the GenericServlet class
public abstract class GenericServlet implements
Servlet, ServletConfig, Serializable
This class provides a basic implementation of the Servlet interface. Since this class
implements the ServletConfig interface, as well, the developer may call ServletConfig
methods directly, without having to obtain a ServletConfig object first. All classes extending
the GenericServlet class should provide an implementation for the service() method.
Methods specific to this class:
public void init()
public void log(String msg)
public void log(String msg, Throwable t)
9.6 the HttpServlet class
It is very likely that the only implementation of the Servlet interface we'll ever use is one that
processes an HTTP request. The servlet API provides such a specific class, namely the
HttpServlet class.
public abstract class HttpServlet extends GenericServlet implements
Serializable
The HttpServlet provides an HTTP specific implementation of the Servlet interface. This
abstract class specifies the following methods:
public void service(ServletRequest req, ServletResponse resp)
public void service(HttpServletRequest req, HttpServletResponse resp)
protected void doGet(HttpServletRequest req, HttpServletResponse resp)
protected void doPost(HttpServletRequest req,
84
9 - SERVLETS
HttpServletResponse resp)
protected void doDelete(HttpServletRequest req,
HttpServletResponse resp)
protected void doOptions(HttpServletRequest req,
HttpServletResponse resp)
protected void doPut(HttpServletRequest req, HttpServletResponse resp)
protected void doTrace(HttpServletRequest req,
HttpServletResponse resp)
9.7 the ServletConfig interface
This interface abstracts configuration information about the servlet, namely:
•
initialization parameters (as name-value pairs)
•
the name of the servlet
•
a ServletContext object, containing web container information
This interface specifies the following methods:
public
public
public
public
String getInitParameter(String name)
Enumeration getInitParameterNames()
ServletContext getServletContext()
String getServletName()
9.8 servlet exceptions
The Java servlet API specifies two servlet specific exceptions:
javax.servlet.ServletException
javax.servlet.UnavailableException
The ServletException class extends java.lang.Exception and can be thrown by the
init(), service(), doXXX() and destroy() methods of the Servlet interface
implementations.
The UnavailableException indicates to the web container that the servlet instance is
unavaialble. It also extends the java.lang.Exception class.
9.9 the servlet lifecycle
Generally, a servlet instance goes through the following stages:
85
9 - SERVLETS
•
instantiation
•
initialization
•
service
•
destroy
•
unavailable
The container creates a servlet instance as first response to an incoming (HTTP) request or at
container startup. Typically, the web container creates a single instance of the servlet, which will
service all incoming requests. If the servlet does not implement the
javax.servlet.SingleThreadModel, concurrent requests are serviced in more than one
service thread, which requires that the service() method be thread safe.
After instantiation, the container calls the init() method of the servlet, method which
performs the initialization of the servlet. Typically, this method contains JDBC driver loading, DB
connection opening, etc.
The web container makes sure that the init() method of the servlet will be completed before
invoking its service() method. Also, the servlet's destroy() method will be called before the
servlet itself is destroyed.
9.10 the ServletRequest interface
Here are some of the methods of this interface:
public
public
public
public
public
public
public
public
public
public
public
public
Object getAttribute(String name)
Object setAttribute(String name, Object attr)
Enumeration getAttributeNames()
int getContentLength()
String getContentType()
String getParameter(String name)
Enumeration getParameterNames()
String[] getParameterValues()
String getServerName()
int getServerPort()
String getRemoteAddr()
String getRemoteHost()
Most of the above methods are self explanatory. But what is the difference between a
parameter and an attribute? While the parameters of the request are part of the request itself, the
attributes of the request are attached by the web containers or by the servlets/JSPs/JSFs.
There are 3 different ways for attaching and retrieving attributes. The first one is to attach
attributes to the request object. The other two use the HttpSession and ServletContext objects,
respectively. The purpose of attributes is to allow the container to provide additional data to a
servlet, JSP or JSF, or to allow sending data from a servlet to another.
86
9 - SERVLETS
9.11 the HttpServletRequest interface
public interface HttpServletRequest extends ServletRequest
This interface contains HTTP specific methods. One has to take in account the structure of an
HTTP request when overviewing the most important methods of this interface. Here are some of
them:
public Cookie[] getCookies()
public long getDateHeader()
public String getHeader(String name)
public Enumeration getHeaders(String name)
public Enumeration getHeaderNames()
public String getContextPath()
public String getPathInfo()
public String getQueryString()
public String getRemoteUser()
9.12 the ServletResponse interface
This interface defines methods for constructing responses to servlet requests.
Here are the most important ones:
public ServletOutputStream getOutputStream()
public PrintWriter getWriter()
public void setContentLength(int len)
public void setContentType(String type)
public void setBufferSize(int size)
public int getBufferSize()
public void flushBuffer()
9.13 the HttpServletResponse interface
This interface extends the ServletResponse interface and defines methods specific for
constructing responses to HTTP requests.
Here are the most important ones:
87
9 - SERVLETS
public void addCookie(Cookie cookie)
public String encodeURL(String url)
public void sendError(int status)
public void sendError(int status, String message)
public void setHeader(String headerName, String value)
public void addHeader(String headerName, String value)
public void setStatus(int statusCode)
9.14 the ServletContext interface
A servlet context defines servlet's view of the web application and provides access to resources
common to all servlets of the web application. Each servlet context is rooted at a specific path in
the web server. The deployment of a web application involves adding an application specific
<context> tag which associates the the name of the application with its root directory. This is
done in server's (container's) server.xml file.
The ServletContext interface abstracts the context of a web application. A reference to an
object of this type can be obtained by invoking the getServletContext() method of the
HttpServlet object.
public String getMIMEType(String fileName)
public String getResource(String path)
public ServletContext getContext(String urlPath)
public String getInitParameter(String name)
public Enumeration getInitParameterNames()
public Object getAttribute(String name)
public Enumeration getAttributeNames()
public void setAttribute(String name, Object attr)
public String removeAttribute(String name)
9.15 the Enroll servlet
The Enroll servlet services the request sent by the web browser when we submit the Enroll form
(file Enroll.html)
Here is its abbreviated form (topics which are DB related are postponed) of the
"EnrollServlet.java" file:
package com.bank11.ccards.servlets;
import java.io.*;
88
9 - SERVLETS
import javax.servlet.*;
import javax.servlet.http.*;
public class EnrollServlet extends HttpServlet
{
public void init(ServletConfig config)
throws ServletException
{
super.init(config);
}
public void doPost(HttpServletRequest req,
HttpServletResponse resp)
throws ServletException, IOException
{
resp.setContentType(“text/html”);
PrintWriter out = resp.getWriter();
// output your page here
out.println("<html>");
out.println("<head>");
out.println("<title>Servlet</title>");
out.println("</head>");
out.println("<body>");
out.println("merge");
out.println("<br>");
out.println("</body>");
out.println("</html>");
out.close();
}
}
89
10 - JDBC
10 - JDBC
10.1 what is jdbc?
JDBC stands for Java Data Base Connectivity and is the Java version of ODBC (Open Data
Base Connectivity). It offers an API for SQL-compliant relational databases access. It abstracts
the vendor-specific details and offers support for the most common database access functions.
The first release of the JDBC specification dates back to Feb. 1997, as part of the Java
Development Kit (JDK) 1.1. After that, JDBC was part of Java Standard Edition (JSE). Starting
with version 3.0, JDBC evolution is part of the Java Community Process. JSR (Java Specification
Request) 54 defines JDBC 3.0 while the current (4.0) JDBC specification is defined in JSR 221.
The JDBC 4.0 API consists of 2 packages:
1. the java.sql package
2. the javax.sql package, which provides several server-side capabilities
The JDBC API provides programmatic access from applications written in the
Java programming language to standard SQL. The JDBC API presents a standard API to access
a wide range of underlying data sources or legacy systems.
10.2 jdbc drivers
Each database vendor offers its own version of DB access API. A JDBC driver is a middleware
layer that translates JDBC calls into vendor specific calls. These drivers fall into four standard
categories, as recognized by the DB industry.
Type 1. JDBC – ODBC Bridge
The driver translates the JDBC calls into equivalent ODBC calls. Both the JDBC and the JDBCODBC calls are invoked within the client application. This solution is inefficient, due to the
multiple layers of indirection involved and to the limitations imposed to the JDBC layer by the
ODBC frame.
The standard JDK includes all classes for this bridge - sun.jdbc.odbc.JdbcOdbcDriver .
90
10 - JDBC
Type 2. Part Java, Part Native Driver
The drivers in this category use a combination of Java implementation and vendor specific
APIs for DB access. The driver translates JDBC specific calls into vendor specific API calls. The
DB returns the result of the call to the API, which in turn, forwards them to the JDBC driver. It is
much faster than the Type 1 drivers, because it eliminates one level of indirection.
Type 3. Intermediate Database Access Server
Type 3 drivers are DataBase servers which act as intermediate tier between multiple clients and
multiple Database servers. The client application sends a JDBC call through a JDBC driver to the
intermediate Database servers. These servers translate the call into a native driver call which
handles the actual DB connection. This type of drivers are implemented by several application
servers, like WebLogic (of BEA Systems) or Inprise Application Server (of Borland).
Type 4. Pure Java Drivers
These are the most efficient drivers. The JDBC API calls are converted to direct network calls
using vendor provided protocols. All major vendors provide type 4 JDBC drivers for their
Database products.
91
10 - JDBC
10.3 the java.sql package
This package contains the core JDBC API. An exhaustive list of the classes and interfaces of
this package can be found in the latest JDBC specification (4.0). The document containing this
specification is JSR 221 and can be viewed at http://jcp.org/en/jsr/detail?id=221.
Of the 80+ classes and interfaces defined in this specification, let's remind some of the most
important ones, defined in the JDBC 3.0 API.
java.sql.Array
java.sql.Blob
java.sql.CallableStatement
java.sql.Clob
java.sql.Connection
java.sql.Date
java.sql.Driver
java.sql.DriverManager
java.sql.PreparedStatement
java.sql.ResultSet
java.sql.ResultSetMetaData
java.sql.SQLData
java.sql.SQLDataException
java.sql.SQLException
java.sql.SQLInput
java.sql.SQLOutput
java.sql.SQLPermission
java.sql.SQLXML
java.sql.SQLWarning
java.sql.Statement
java.sql.Struct
java.sql.Time
java.sql.Timestamp
java.sql.Types
java.sql.Wrapper
92
10 - JDBC
The following list contains all of the classes and interfaces new or updated in version 4.0.
java.sql.Blob
java.sql.CallableStatement
java.sql.Clob
java.sql.ClientinfoStatus
java.sql.Connection
java.sql.DatabaseMetaData
java.sql.NClob
java.sql.PreparedStatement
java.sql.ResultSet
java.sql.RowId
java.sql.RowIdLifeTime
java.sql.SQLClientInfoException
java.sql.SQLDataException
java.sql.SQLException
java.sql.SQLFeatureNotSupportedException
java.sql.SQLInput
java.sql.SQLIntegrityConstraintViolationException
java.sql.SQLInvalidAuthorizationSpecException
java.sql.SQLNonTransientConnectionException
java.sql.SQLNonTransientException
java.sql.SQLOutput
java.sql.SQLSyntaxErrorException
java.sql.SQLTimeoutException
java.sql.SQLTransactionRollbackException
java.sql.SQLTransientConnectionException
java.sql.SQLTransientException
java.sql.SQLXML
java.sql.SQLWarning
java.sql.Statement
java.sql.Types
java.sql.Wrapper
javax.sql.CommonDataSource
javax.sql.StatementEvent
javax.sql.StatementEventListener
10.4 interaction schema in the java.sql package
The figure below shows the interactions and relationships between the major classes and
interfaces of the java.sql package.
The main steps in communicating with a database are:
1. loading a database driver
2. establishing a database connection
3. querying the database
4. processing the result set
93
10 - JDBC
10.5 loading a DB driver connecting to the database
There are two main steps in connecting to an existing database. The first one is
loading a database driver.
A database driver is specified by the driver name. Here are some examples of actual database
driver names:
•
•
•
•
•
com.borland.datastore.jdbc.DataStoreDriver
com.sybase.jdbc.SybDriver
com.ibm.db2.jdbc.net.DB2Driver
oracle.jdbc.driver.OracleDriver
sun.jdbc.odbc.JdbcOdbcDriver
94
10 - JDBC
The Java code to load the driver name is somewhat obscure, but let's take it for granted:
import java.sql.*;
import java.util.*;
try
{
Class.forName("org.gjt.mm.mysql.Driver").newInstance();
} catch (Exception e) {
// driver not found
e.printStackTrace();
}
The actual location of the database is specified by its URL (also known as connection URL).
The URL has 3 parts separated by colons, as follows:
jdbc:<subprotocol>:subname
•
jdbc is the protocol name (actually, the only protocol allowed in JDBC).
•
the sub-protocol is used to identify the JDBC driver, as specified by the driver vendor.
•
subname – the syntax of this field is vendor specific and allows the identification
Here are some examples of JDBC driver URLs:
•
jdbc:sybase:localhost:2025
•
jdbc:db2://db2.bank11.com:50002/ccards
•
jdbc:oracle:thin:@loclahost:1521:ORCL
The second step in connecting to an existing database is to open the connection, by using the
connection URL.
Here is some sample code which shows how this is done:
String connURL = "jdbc:mysql://localhost:3306/ccards";
String user = "root";
String passwd = "root"
Connection conn = DriverManager.getConnection(connURL,
user, passwd);
Since we just used it, let's have a better look in the next section at the DriverManager class.
95
10 - JDBC
10.6 the DriverManager class
This class belongs to the javax.sql package and offers a common access layer on top of
different JDBC drivers. Each driver used by the application must be registered (loaded) before the
DriverManager class tries to obtain a connection.
There are 3 versions of the getConnection() method of the DriverManager class. Here
they are:
public static Connection getConnection(String connURL)
throws SQLException
public static Connection getConnection(String connURL, String user,
String passwd) throws SQLException
public static Connection getConnection(String connURL,
java.util.Properties info) throws SQLException
While the first two forms of getConnection() are pretty straightforward, let's see an example of
how to use the last of the three forms.
Properties prp = new Properties();
prp.put("autocommit", "true");
prp.put("create", "true");
Connection conn = DriverManager.getConnection(connURL, prp);
10.7 the Connection interface
The Connection interface is part of then javax.sql package. Once we get the hold of a
Connection object, we can use it for various purposes, but we will restrict ourselves to creating
SQL statements. The most important methods for creating statements:
Statement createStatement() throws SQLException
Statement createStatement(int resultSetType, int resultSetConcurrency)
throws SQLException
Statement createStatement(int resultSetType, int resultSetConcurrency,
int resultSetHoldability)
PreparedStatement prepareStatement(String sql)
throws SQLException
CallableStatement prepareCall(String sql)
throws SQLException
96
10 - JDBC
10.8 statement interfaces
The objects we encountered in the previous section, namely, Statement,
PreparedStatement and CallableStatement abstract regular SQL statements, prepared
statements and stored procedures, respectively.
The Statement interface has (among others) the following methods:
1. methods for executing statements:
•
execute()
•
executeQuery()
•
executeUpdate()
2. methods for batch updates:
•
addBatch()
•
executeBatch()
•
clearBatch()
3. methods for result set fetch size and direction:
•
setFetchSize()
•
getFetchSize()
•
setFetchDirection()
•
getFetchDirection()
4. method to get the current result set:
•
getResultSet()
5. methods for result set concurrency and type:
•
getResultSetConcurrency()
•
getResultSetType()
6. other methods:
•
setQueryTimeout()
•
getQueryTimeout()
•
setMaxFieldSize()
•
getMaxFieldSize()
•
cancel()
•
getConnection()
97
10 - JDBC
The Statement interfaces also support the same methods for transaction support as the
Connection objects.
Objects implementing the Connection interface are mainly used for SQL queries execution.
Here is a typical example:
Statement stmt = conn.createStatement();
String sqlString = "CREATE TABLE customer ...";
stmt.executeUpdate(sqlString);
10.9 the ResultSet interface
The result of a query by a Statement object is a java.sql.ResultSet object which is
available to the user and allows access to the data retrieved. The interface ResultSet is
implemented by driver vendors.
Methods to retrieve data:
•
getAsciiStream()
•
getBoolean()
•
getDate()
•
getInt()
•
getShort()
•
getTimeStamp()
•
getBinaryStream()
•
getBytes()
•
getFloat()
•
getObject()
•
getTime()
•
getString()
•
getByte()
•
getDouble()
•
getLong()
•
getBigDecimal()
•
getMetaData()
•
getClob()
•
getWarnings()
•
getBlob()
98
10 - JDBC
Most of these methods require the column index (which in SQL starts at 1, not at 0) or the
column name, as the argument.
The usage of these retrieval methods assumes the prior knowledge of the type and the index
(or name) of a particular column. What if we don't have this knowledge? Fortunately, all this data
about the DB schema (or metadata) can be retrieved using the ResultSetMetaData interface.
The invocation of the getMetaData() method of a ResultSet object returns an object of
ResultSetMetaData type.
Here are the most important methods specified by the ResultSetMetaData interface:
•
getCatalogName()
•
getTableName()
•
getSchemaName()
•
getColumnCount()
•
getColumnName()
•
getColumnLabel()
•
getColumnType()
•
getColumnTypeName()
•
getColumnClassName()
•
getColumnDisplaySize()
•
getScale()
•
getPrecision()
•
isNullable()
•
isCurrency()
•
isSearchable()
•
isCaseSensitive()
•
isSigned()
•
isAutoIncrement()
•
isReadOnly()
•
isDefinitelyWritable()
10.10 ResultSet characteristics
By default, all created ResultSets have a type of forward only, a concurrency of read only, and
cursors are held over commit boundaries. An exception to this is that WebSphere currently
changes the cursor holdability default so that cursors are implicitly closed when committed. These
characteristics are configurable through methods that are accessible on Statement,
PreparedStatement, and CallableStatement objects.
A cursor comprises a control structure for the successive traversal (and potential processing)
of records in a result set. One can think of a database cursor as an iterator over the collection of
rows in the result set.
99
10 - JDBC
10.10.1 ResultSet types
The ResultSet type specifies the following about the ResultSet:
•
•
Whether the ResultSet is scrollable.
The types of Java (TM) Database Connectivity (JDBC) ResultSets that are defined by
constants on the ResultSet interface.
Definitions of these ResultSet types are as follows:
TYPE_FORWARD_ONLY
A cursor that can only be used to process from the beginning of a ResultSet to the end of it.
This is the default type.
TYPE_SCROLL_INSENSITIVE
A cursor that can be used to scroll in various ways through a ResultSet. This type of cursor is
insensitive to changes made to the database while it is open. It contains rows that satisfy the
query when the query was processed or when data is fetched.
TYPE_SCROLL_SENSITIVE
A cursor that can be used to scroll in various ways through a ResultSet. This type of cursor is
sensitive to changes made to the database while it is open. Changes to the database have a
direct impact on the ResultSet data.
JDBC 1.0 ResultSets are always forward only. Scrollable cursors were added in JDBC 2.0.
Note: The blocking enabled and block size connection properties affect the degree of sensitivity
of a TYPE_SCROLL_SENSITIVE cursor. Blocking enhances performance by caching data in the
JDBC driver layer itself.
10.10.2 Concurrency
Concurrency determines whether the ResultSet can be updated. The types are again defined by
constants in the ResultSet interface. The available concurrency settings are as follows:
CONCUR_READ_ONLY
A ResultSet that can only be used for reading data out of the database. This is the default
setting.
CONCUR_UPDATEABLE
A ResultSet that allows you to make changes to it. These changes can be placed into the
underlying database.
JDBC 1.0 ResultSets are always forward only. Updateable ResultSets were added in JDBC 2.0.
Note: According to the JDBC specification, the JDBC driver is allowed to change the ResultSet
type of the ResultSet concurrency setting if the values cannot be used together. In such cases,
the JDBC driver places a warning on the Connection object.
There is one situation where the application specifies a TYPE_SCROLL_INSENSITIVE,
CONCUR_UPDATEABLE ResultSet. Insensitivity is implemented in the database engine by
making a copy of the data. You are then not allowed to make updates through that copy to the
underlying database. If you specify this combination, the driver changes the sensitivity to
TYPE_SCROLL_SENSITIVE and create the warning indicating that your request has been
changed.
10.10.3 Holdability
The holdability characteristic determines whether calling commit on the Connection object
closes the ResultSet. The JDBC API for working with the holdability characteristic is new in
version 3.0. However, the native JDBC driver has provided a connection property for several
100
10 - JDBC
releases that allows you to specify that default for all ResultSets created under the connection.
The API support overrides any setting for the connection property. Values for the holdability
characteristic are defined by ResultSet constants and are as follows:
HOLD_CURSOR_OVER_COMMIT
All open cursors remain open when the commit clause is called. This is the native JDBC default
value.
CLOSE_CURSORS_ON_COMMIT
All open cursors are closed when commit clause is called.
10.11 example of data retrieval
// DisplayServlet.java
package com.bank11.ccards.servlets;
import
import
import
import
import
java.sql.*;
javax.servlet.*;
javax.servlet.http.*;
java.math.*;
java.util.*;
public class DisplayServlet extends HttpServlet {
Connection conn;
// Initializes the servlet
public void init(ServletConfig config) throws ServletException {
super.init(config);
String driverName = "org.gjt.mm.mysql.Driver";
try {
Class.forName("org.gjt.mm.mysql.Driver");
}
catch(ClassNotFoundException e) {
e.printStackTrace();
}
String connURL="jdbc:mysql://localhost:3306/ccards";
try {
conn=DriverManager.getConnection(connURL,"root","root");
} catch (SQLException sqle) {
sqle.printStackTrace();
}
}
// Destroys the servlet.
101
10 - JDBC
public void destroy() {
}
// Processes requests for both HTTP GET and POST methods.
protected void processRequest(HttpServletRequest req,
HttpServletResponse resp) throws ServletException, java.io.IOException {
String theCode = req.getParameter(“CODE”);
String sql = “SELECT FIRST_NAME, LAST_NAME, ACCOUNT_NUM from
CUSTOMERS where CNP=”+theCode+”;”;
try {
Statement stmt = conn.getStatement();
ResultSet rs = stmt.executeQuery(sql);
while(rs.next()) {
String firstName = rs.getString(“FIRST_NAME”);
String lastName = rs.getString(“LAST_NAME”);
BigDecimal accountNum = rs.getBigDecimal(“ACCOUNT_NUM”);
}
} catch (SQLException sqle) {
sqle.printStackTrace();
} catch (Exception e) {
e.printStackTrace();
}
resp.setContentType("text/html");
java.io.PrintWriter out = resp.getWriter();
// output your page here
out.println("<html>");
out.println("<head>");
out.println("<title>Servlet</title>");
out.println("</head>");
out.println("<body>");
...
out.println("</body>");
out.println("</html>");
out.close();
}
// Handles the HTTP GET method.
protected void doGet(HttpServletRequest req, HttpServletResponse
resp) throws ServletException, java.io.IOException {
processRequest(req, resp);
}
// Handles the HTTP POST method.
protected void doPost(HttpServletRequest req, HttpServletResponse
resp) throws ServletException, java.io.IOException {
102
10 - JDBC
processRequest(req, resp);
}
// Returns a short description of the servlet.
public String getServletInfo() {
return "Short description";
}
}
10.12 the PreparedStatement interface
If an SQL statement is used several times and its different forms differ only with respect to the
data they specify, a better choice is the usage of a PreparedStatement object. Prepared
statements are parametrized and each parameter (usually, a field (column) value or name) is
represented by a question mark '?'.
The following lines of Java code give an example of how to use PreparedStatement objects:
Statement stmt = con.createStatement();
PreparedStatement pstmt = con.prepareStatement("INSERT INTO customer
VALUES (?, ?, ?)");
stmt.executeUpdate("CREATE TABLE customer
varchar(32) lastName varchar(24))");
(id int, firstName
// set parameters for preparedStatement
pstmt.setInt(1, 1021);
pstmt.setString(2, "Vasile");
pstmt.setString(3, "Dumitrascu");
int count = pstmt.executeUpdate();
10.13 jdbc and sql types and their corresponding java classes
JDBC Type
Purpose
SQL Type
Java Type
ARRAY
SQL array
ARRAY
java.sql.Array
BIGINT
64 bit integer
BIGINT
long
BINARY
binary value
none
byte[]
BIT
one bit value
BIT
boolean
BLOB
binary large object
BLOB
java.sql.Blob
CHAR
char string
CHAR
String
CLOB
character large object
CLOB
java.sql.Clob
DATE
day, month, year
DATE
java.sql.Date
103
10 - JDBC
JDBC Type
Purpose
SQL Type
Java Type
DECIMAL
decimal value
DECIMAL
DISTINCT
distinct
DISTINCT
none
DOUBLE
double precision
DOUBLE PRECISION
double
FLOAT
double precision
FLOAT
double
INTEGER
32 bit integer
INTEGER
int
JAVA_OBJECT
stores Java objects
none
Object
variable length binary
value
none
byte[]
LONGVARBINARY
java.math.Big
Decimal
LONGVARCHAR
variable length char string
none
String
NULL
null values
NULL
null
NUMERIC
decimal value
NUMERIC
OTHER
db specific types
none
Object
REAL
single precision
REAL
float
16 bit integer
SMALLINT
short
TIME
hrs, mins, secs
TIME
java.sql.Time
TIMESTAMP
date, time, nanoseconds
TIMESTAMP
TINYINT
8 bit integer
TINYINT
short
none
byte[]
VARCHAR
String
java.math.Big
Decimal
REF
SMALLINT
STRUCT
VARBINARY
VARCHAR
variable length binary
value
variable length char string
java.sql.Times
tamp
10.14 JDBC Data Sources
In the JDBC 2.0 optional package, the DriverManager interface is replaced by the
DataSource interface as main method of obtaining DB connections.
While the DriverManager interface was used at run time to load explicitly a JDBC driver, the
new mechanism uses a centralized JNDI service to locate a javax.sql.DataSource object.
This interface is, basicly, a factory for creating DB connections. It is part of the javax.sql
package.
The DataSource interface is implemented by a driver vendors. There are three types of
implementations:
1. Basic implementation -- produces a standard Connection object
2. Connection pooling implementation -- produces a Connection object that will
104
10 - JDBC
automatically participate in connection pooling. This implementation works with a middletier connection pooling manager.
3. Distributed transaction implementation -- produces a Connection object that may be
used for distributed transactions and almost always participates in connection pooling.
This implementation works with a middle-tier transaction manager and almost always with
a connection pooling manager.
Main methods:
public Connection getConnection() throws SQLException
public Connection getConnection(String user, String pwd)
SQLException
throws
A servlet example using the DataSource interface:
package com.bank11.ccards.servlets;
import
import
import
import
import
import
java.io.*;
java.sql.*;
javax.servlet.*;
javax.servlet.http.*;
javax.naming.*;
javax.sql.*;
public class TestDataSource extends HttpServlet
{
private final static Logger log =
Logger.getLogger(TestDataSource.class.getName());
private final static String DATASOURCE_NAME = "jdbc/ccards";
private DataSource theDataSource;
public void setDataSource(DataSource dataSource)
{
theDataSource = dataSource;
}
public DataSource getDataSource()
{
return theDataSource;
}
public void init() throws ServletException
{
if (theDataSource == null) {
try {
Context env =
(Context) new InitialContext().lookup("java:comp/env");
theDataSource = (DataSource) env.lookup(DATASOURCE_NAME);
105
10 - JDBC
if (theDataSource == null)
throw new ServletException("`" + DATASOURCE_NAME +
"' is an unknown DataSource");
} catch (NamingException e) {
throw new ServletException(e);
}
}
}
public void doGet(HttpServletRequest request, HttpServletResponse
response) throws IOException, ServletException
{
...
}
}
106
11 - JSP
11 - JSP
11.1 java server pages as part of web applications
A Java Server Page (JSP) is a standard HTML or XML file which contains new scripting tags.
A JSP is loaded by a JSP container and is converted (to servlet code). If the JSP is modified,
the servlet code is regenerated.
The current JSP specification is JSP 2.1 and is related to the 2.5 Java Servlet specification.
JSR 245 is the official document containing the current specification of JSP.
The JSP specific interfaces, classes and exceptions are part of two packages, namely
javax.servlet.jsp and javax.servlet.jsp.tagext.
The javax.servlet.jsp package contains a number of classes and interfaces that describe and
define the contracts between a JSP page implementation class and the runtime environment
provided for an instance of such a class by a conforming JSP container.
The package javax.servlet.jsp defines two interfaces – JspPage and HttpJspPage. The
interface HttpJspPage is the interface that a JSP processor-generated class for the HTTP protocol
must satisfy. The JspPage interface is the interface that a JSP processor-generated class must
satisfy.
The package javax.servlet.jsp.tagext contains classes and interfaces for the definition of
JavaServer Pages Tag Libraries.
11.2 the java.servlet.jsp.JspPage interface
This interface has 2 methods:
public void jspInit()
public void jspDestroy()
The javax.servlet.HttpJspPage interface has a single method:
public void jspService(HttpServletRequest req,
HttpServletResponse resp) throws ServletException, IOException
The implementation of this method is generated by the web container – never by the developer.
11.3 the generated servlet – an example
107
11 - JSP
Even if we start with a very benign java server page, like the listed “hello world” example below,
the generated servlet is still pretty complex.
First, the original index.jsp file.
<%-Document
: index
Created on : 08.11.2010, 08:17:39
Author
: sm
--%>
<%@page contentType="text/html" pageEncoding="UTF-8"%>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"
"http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html;
charset=UTF-8">
<title>JSP Page</title>
</head>
<body>
<h1>Hello World!</h1>
</body>
</html>
The generated servlet follows.
package org.apache.jsp;
import javax.servlet.*;
import javax.servlet.http.*;
import javax.servlet.jsp.*;
public final class index_jsp extends
org.apache.jasper.runtime.HttpJspBase
implements org.apache.jasper.runtime.JspSourceDependent {
private static final JspFactory _jspxFactory =
JspFactory.getDefaultFactory();
private static java.util.Vector _jspx_dependants;
private org.glassfish.jsp.api.ResourceInjector
_jspx_resourceInjector;
public Object getDependants() {
108
11 - JSP
return _jspx_dependants;
}
public void _jspService(HttpServletRequest request,
HttpServletResponse response)
throws java.io.IOException, ServletException {
PageContext pageContext = null;
HttpSession session = null;
ServletContext application = null;
ServletConfig config = null;
JspWriter out = null;
Object page = this;
JspWriter _jspx_out = null;
PageContext _jspx_page_context = null;
try {
response.setContentType("text/html;charset=UTF-8");
response.setHeader("X-Powered-By", "JSP/2.1");
pageContext = _jspxFactory.getPageContext(this, request,
response, null, true, 8192, true);
_jspx_page_context = pageContext;
application = pageContext.getServletContext();
config = pageContext.getServletConfig();
session = pageContext.getSession();
out = pageContext.getOut();
_jspx_out = out;
_jspx_resourceInjector =
(org.glassfish.jsp.api.ResourceInjector)
application.getAttribute("com.sun.appserv.jsp.resource.injector");
out.write("\n");
out.write("\n");
out.write("\n");
out.write("<!DOCTYPE HTML PUBLIC \"-//W3C//DTD HTML 4.01
Transitional//EN\"\n");
out.write("
\"http://www.w3.org/TR/html4/loose.dtd\">\n");
out.write("\n");
out.write("<html>\n");
out.write("
<head>\n");
out.write("
<meta http-equiv=\"Content-Type\"
content=\"text/html; charset=UTF-8\">\n");
out.write("
<title>JSP Page</title>\n");
out.write("
</head>\n");
out.write("
<body>\n");
out.write("
<h1>Hello World!</h1>\n");
out.write("
</body>\n");
out.write("</html>\n");
109
11 - JSP
} catch (Throwable t) {
if (!(t instanceof SkipPageException)){
out = _jspx_out;
if (out != null && out.getBufferSize() != 0)
out.clearBuffer();
if (_jspx_page_context != null)
_jspx_page_context.handlePageException(t);
else throw new ServletException(t);
}
} finally {
_jspxFactory.releasePageContext(_jspx_page_context);
}
}
}
A short comment. The class HttpJspBase is a vendor-implemented class, whose declaration
clarifies its relationship with the standard JSP classes and interfaces.
public abstract class HttpJspBase extends
javax.servlet.http.HttpServlet implements javax.servlet.jsp.HttpJspPage
11.4 ordinary java beans
A java bean is a java class which:
•
implements the java.io.Serializable interface
•
provides a no-argument constructor
•
for each of its properties, provides get and set methods
•
implements a property change mechanism
Here is a typical example of a java bean.
/*
* NewBean.java
*/
import java.beans.*;
import java.io.Serializable;
/**
* @author sm
*/
public class NewBean extends Object implements Serializable {
110
11 - JSP
public static final String PROP_SAMPLE_PROPERTY =
"sampleProperty";
private String sampleProperty;
private PropertyChangeSupport propertySupport;
public NewBean() {
propertySupport = new PropertyChangeSupport(this);
}
public String getSampleProperty() {
return sampleProperty;
}
public void setSampleProperty(String value) {
String oldValue = sampleProperty;
sampleProperty = value;
propertySupport.firePropertyChange(PROP_SAMPLE_PROPERTY,
oldValue, sampleProperty);
}
public void addPropertyChangeListener(PropertyChangeListener
listener) {
propertySupport.addPropertyChangeListener(listener);
}
public void removePropertyChangeListener(PropertyChangeListener
listener) {
propertySupport.removePropertyChangeListener(listener);
}
}
11.5 jsp tags
There are 3 categories of JSP tags (elements):
1. directives – affect the structure of the whole jsp
2. scripting elements – java code inserted in the JSP page
3. actions – special tags affecting the run time behaviour of the JSP
Rules for JSP tags:
•
attribute values are always quoted (single or double quotes)
•
URLs follow the servlet conventions
111
11 - JSP
•
if the URL does not start with / , it is interpreted relative to the position of the current JSP
11.6 jsp directives
The JSP directives are messages sent by the Java Server Page to the JSP container. These
directives do not produce any client output and affect the whole JSP file.
The general format of a JSP directive is as follows:
<%@directive_name attr1="val1" ... attrn="valn" %>
Ther are three JSP directives: page, include and taglib.
The page directive format:
<%@page attr1="val1" ... %>
attributes:
•
language – values: "java"
•
extends – superclass of the generated class
•
import – list of packages classes
•
session – "true" or "false", the implicit session object is available
•
buffer – buffering model for the output stream
•
autoflush – if "true", the buffer is flushed automatically if full
•
isThreadSafe – "true" or "false"
•
isErrorPage – "true" or "false"
•
contentType – MIME type of the response
•
info
•
errorPage – the URL of an error page, in case of error
The include directive instructs the container to include inline the content of the resource
specified by "fileName". The format of this directive:
<%@include file="fileName" %>
The taglib directive allows the usage of custom tags (tag extensions). It has the following
format:
<%@taglib uri="tagLibUri" prefix="tagPrefix" %>
where the tagPrefix indicates a name scope.
112
11 - JSP
11.7 scripting elements
11.7.1 declarations
<%! java vars and method declarations %>
Basicly, a bloc of java code used to define class-wide variables and methods in the generated
servlet.
11.7.2 scriptlets
<% valid java statements %>
Block of java code which is executed during request processing. In Tomcat, this code goes to
inside the service() method.
11.7.3 expressions
<%= java expressions to be evaluated %>
A scriptlet that sends a value of a Java expression to back to the client. It is evaluated at
request processing time and the result is converted to a string which is then displayed.
11.7.4 standard actions
Tags that affect the runtime behaviour of the JSP and the response to the client. A tag can be
embedded into a JSP page. The standard actions are detailed in the next paragraphs.
11.8 the useBean standard action
<jsp:useBean>
Used to instantiate a Java bean or locate a bean instance. Assigns it to available name or id.
The syntax for this action is:
<jsp:useBean
id="beanName" scope="sName" beandetails />
113
11 - JSP
where beandetails is one of the following:
•
class="className"
•
class="className" type="typeName"
•
beanName="beanName" type="typeName"
•
type="typeName"
11.9 the setProperty standard action
<jsp:setProperty>
Used in conjunction with the <jsp:useBean> action to set the value of the bean properties.
The syntax for this action is:
<jsp:setProperty name="beanName" propertydetails />
where propertydetails is one of the following:
•
property="*"
•
property="propertyName"
•
property="propertyName" param="parameterName"
•
property="propertyName" value="propertyValue"
where propertyValue is a string or a scriptlet.
Attributes description:
•
name - the name of a bean instance, already defined in a <jsp:useBean>
•
property – specifies the relationship between request parameters and corresponding
bean properties
•
property="*" - stores all of the values in the request object parameters (called request
parameters) in matching Bean properties. The property names in the Bean must match
the request parameters
property="propertyName" [ param="parameterName" ] - Sets one Bean property to
the value of one request parameter. The request parameter can have a different name
than the Bean property, and if so, you must specify param.
property="propertyName" value="{ string | <%= expression %> }" - Sets one Bean
property to a specific value. The value can be a String or an Expression
•
•
11.10 the getProperty standard action
<jsp:getProperty>
114
11 - JSP
Used to access the properties of a bean, converts them to string and displays the output to the
client.
The syntax for this action is:
<jsp:getProperty name="beanName" property="propName" />
Attributes description:
•
name - the name of a bean instance whose property is to be retrieved
•
property - name of the property to be retrieved
11.11 the param standard action
<jsp:param>
Provide other tags with additional information in the form of name:value pairs. It is used in
conjunction with the <jsp:include>, <jsp:forward>, <jsp:plugin> actions.
The syntax for this action is:
<jsp:param name="paramName" value="paramValue" />
11.12 the include standard action
<jsp:include>
Used for the inclusion of a static or dynamic resource into the current JSP page at request
processing time. An included page has access only to the JspWriter object and cannot set
headers or cookies. While the <%@include> directive is executed at compile time and has static
content, the <jsp:include> action is executed at request processing time and has static or dynamic
content.
The syntax for this action is:
<jsp:include page="pageURL" flush="true" />
Attributes description:
•
page - the URL of the page, same format as the <%@include> directive.
•
flush - only the "true" value is supported.
11.13 the forward standard action
115
11 - JSP
<jsp:forward>
Used to forward the the request to another JSP, servlet or to a static resource..
The syntax for this action is:
<jsp:forward page="pageURL" />
The action may include several <jsp:param> tags, as well. It is used mainly, when we want to
separate the application into different views, depending on request.
11.14 the plugin standard action
<jsp:plugin>
Used in pages to generate client browser specific HTML tags (<OBJECT> or <EMBED>) that
result in download of Java plugins(if required), followed by the execution of the applet or
JavaBeans component specified by the tag.
The syntax for this action is:
<jsp:plugin type="bean|applet" code="objCode" codeBase="objCodeBase"
align="align" archive="archiveList" height="height" hspace="hSpace"
jreversion="jreVersion" name="componentName" vspace="vSpace"
width="width" nspluginurl="netscapeURL" iepluginurl="IEURL">
<jsp:params>
<jsp:param name="paramName" value="paramValue" />
...
</jsp:params>
</jsp:plugin>
Attributes description:
•
name - the name of a bean instance, already defined in a <jsp:useBean>
•
type="bean|applet" - the type of object the plugin will execute. You must specify either
bean or applet, as this attribute has no default value.
•
code="classFileName" - the name of the Java class file that the plugin will execute. You
must include the .class extension in the name following code. The filename is relative to
the directory named in the codebase attribute.
•
codebase="classFileDirectoryName" - the absolute or relative path to the directory that
contains the applet's code. If you do not supply a value, the path of the JSP file that calls
<jsp:plugin> is used.
•
name="instanceName" - a name for the Bean or applet instance, which makes it
possible for applets or Beans called by the same JSP file to communicate with each
other.
•
archive="URIToArchive, ..." - a comma-separated list of paths that locate archive files
116
11 - JSP
to be preloaded with a class loader located in the directory named in codebase.
•
align="bottom|top|middle|left|right" - the positioning of the image displayed by
the applet or Bean relative to the line in the JSP result page that corresponds to the line in
the JSP file containing the <jsp:plugin> tag.
•
height="displayPixels" width="displayPixels" - the initial height and width, in pixels, of
the image the applet or Bean displays, not counting any windows or dialog boxes the
applet or Bean brings up.
•
hspace="leftRightPixels" vspace="topBottomPixels" - the amount of space, in pixels,
to the left and right (or top and bottom) of the image the applet or Bean displays. Must be
a small nonzero number.
•
jreversion="JREVersionNumber|1.1" - the version of the Java Runtime Environment
(JRE) the applet or Bean requires. The default value is 1.1.
•
nspluginurl="URLToPlugin" - the URL where the user can download the JRE plugin for
Netscape Navigator. The value is a full URL, with a protocol name, optional port number,
and domain name.
•
iepluginurl="URLToPlugin"
11.15 implicit objects
JSP provides several implicit objects, based on the servlet API, objects which are automaticly
available.
1. request - represents the object that triggered the service() method invokation and has
type HttpServletRequest with scope request
2. response - represents server's response to the request, it has HttpServletResponse
type and page scope
3. pageContext - provides a single point of access to attributes and shared data within the
page, it has type PageContext with scope page
4. session - it has HttpSession type and session scope
5. application - represents the servlet context, it has type ServletContext and scope
application
6. out - it represents the buffered version of java.io.PrintWriter, writes to the output
stream to the client, it has javax.servlet.jsp.JspWriter type and scope page
7. config - it is the SevletConfig for the current JSP page, it is of type ServletConfig and
has page scope
8. page - it is an instance of the page's implementation of the servlet class, it has
java.lang.Object type and scope page
11.16 scopes
1. request - an object with request scope is bound to the HttpServletRequest object; the
object can be accessed by invoking the getAttribute() method on the implicit
117
11 - JSP
request object; the generated servlet binds the object to HttpServletRequest object
using the setAttribute(String key, Object value) method
2. session - an object with session scope is bound to the HttpSession object; the object
can be accessed by invoking the getValue() method on the implicit session object; the
generated servlet binds the object to HttpSession object using the
setAttribute(String key, Object value) method
3. application - an object with application scope is bound to the ServletContext object;
the object can be accessed by invoking the getAttribute() method on the implicit
application object; the generated servlet binds the object to the ServletContext
object using the setAttribute(String key, Object value) method
4. page - an object with page scope is bound to the PageContext object; the object can be
accessed by invoking the getAttribute() method on the implicit pageContext object;
the generated servlet binds the object to PageContext object using the
setAttribute(String key, Object value) method
11.17 a short example
The following is the Enroll.jsp file.
<%@page contentType="text/html" errorPage="error.jsp"%>
<jsp:useBean id="enrollBean" scope="session"
class="com.bank11.ccards.beans.EnrollBean" />
<jsp:setProperty name="enrollBean" property="*" />
<%
enrollBean.init();
if (enrollBean.invalidAcct())
{ %>
<jsp:forward page="retry.jsp">
<jsp:param name="resolution" value="invalidAcct"/>
</jsp:forward>
<% }
else if (enrollBean.registeredAcct())
{ %>
<jsp:forward page="response.jsp">
<jsp:param name="resolution" value="registeredAcct"/>
</jsp:forward>
<% }
else if (enrollBean.userExists())
{ %>
<jsp:forward page="retry.jsp">
<jsp:param name="resolution" value="userExists"/>
</jsp:forward>
118
11 - JSP
<% }
else
{
enrollBean.register(); %>
<jsp:forward page="response.jsp">
<jsp:param name="resolution" value="userEnrolled"/>
</jsp:forward>
<% }
%>
11.18 an extended example
This example is provided by Devsphere, a software development and consulting company.
11.18.1 Data beans
SimpleBean is a Java bean that contains several standard properties (a String, a float, an int, a
boolean and another String), two indexed standard properties (a String[] and an int[]) and another
data bean (a SimpleSubBean). The SimpleBean class is declared public, has a no-arg constructor
and provides accessors (get & set methods) for its properties. The public constructor could have
been omitted, since the Java compiler generates one in the absence of any other constructors.
SimpleBean.java:
package com.devsphere.examples.mapping.simple;
// Simple bean
public class SimpleBean implements java.io.Serializable {
private String string;
private float number;
private int integer;
private boolean flag;
private String colors[];
private int list[];
private String optional;
private SimpleSubBean subBean;
// No-arg constructor
public SimpleBean() {
}
// Gets the string property
public String getString() {
return this.string;
}
// Sets the string property
public void setString(String value) {
119
11 - JSP
this.string = value;
}
// Gets the number property
public float getNumber() {
return this.number;
}
// Sets the number property
public void setNumber(float value) {
this.number = value;
}
// Gets the integer property
public int getInteger() {
return this.integer;
}
// Sets the integer property
public void setInteger(int value) {
this.integer = value;
}
// Gets the flag property
public boolean getFlag() {
return this.flag;
}
// Sets the flag property
public void setFlag(boolean value) {
this.flag = value;
}
// Gets the colors property
public String[] getColors() {
return this.colors;
}
// Sets the colors property
public void setColors(String values[]) {
this.colors = values;
}
// Gets an element of the colors property
public String getColors(int index) {
return this.colors[index];
}
120
11 - JSP
// Sets an element of the colors property
public void setColors(int index, String value) {
this.colors[index] = value;
}
// Gets the list property
public int[] getList() {
return this.list;
}
// Sets the list property
public void setList(int values[]) {
this.list = values;
}
// Gets an element of the list property
public int getList(int index) {
return this.list[index];
}
// Sets an element of the list property
public void setList(int index, int value) {
this.list[index] = value;
}
// Gets the optional property
public String getOptional() {
return this.optional;
}
// Sets the optional property
public void setOptional(String value) {
this.optional = value;
}
// Gets the subBean property
public SimpleSubBean getSubBean() {
return this.subBean;
}
// Sets the subBean property
public void setSubBean(SimpleSubBean value) {
this.subBean = value;
}
}
121
11 - JSP
SimpleSubBean contains only two standard properties (a String and a float).
SimpleSubBean.java:
package com.devsphere.examples.mapping.simple;
// Simple sub-bean
public class SimpleSubBean implements java.io.Serializable {
private String string;
private float number;
// No-arg constructor
public SimpleSubBean() {
}
// Gets the string property
public String getString() {
return this.string;
}
// Sets the string property
public void setString(String value) {
this.string = value;
}
// Gets the number property
public float getNumber() {
return this.number;
}
// Sets the number property
public void setNumber(float value) {
this.number = value;
}
}
11.18.2 the HTML Form
The properties of SimpleBean are mapped to the form elements of SimpleForm.html:
Name
Property type
Element type
string
String
text
number
float
text
integer
int
radio[]
flag
boolean
checkbox
122
11 - JSP
colors
String[]
checkbox[]
list
int[]
select
optional
String
text
subBean.string
String
text
subBean.number
float
text
SimpleForm.html:
<HTML>
<HEAD><TITLE>Simple form</TITLE></HEAD>
<BODY>
<H3>Simple Example</H3>
<FORM METHOD="POST">
<P> String <BR>
<INPUT TYPE="TEXT" NAME="string" SIZE="20">
<P> Number <BR>
<INPUT TYPE="TEXT" NAME="number" SIZE="20">
<P> Integer <BR>
<INPUT TYPE="RADIO" NAME="integer" VALUE="1">Option 1
<INPUT TYPE="RADIO" NAME="integer" VALUE="2">Option 2
<INPUT TYPE="RADIO" NAME="integer" VALUE="3">Option 3
<P> Flag <BR>
<INPUT TYPE="CHECKBOX" NAME="flag">Flag
<P> Colors <BR>
<INPUT TYPE="CHECKBOX" NAME="colors" VALUE="red">Red
<INPUT TYPE="CHECKBOX" NAME="colors" VALUE="green">Green
<INPUT TYPE="CHECKBOX" NAME="colors" VALUE="blue">Blue
<P> List <BR>
<SELECT NAME="list" SIZE="3" MULTIPLE>
<OPTION VALUE="1">Item 1</OPTION>
<OPTION VALUE="2">Item 2</OPTION>
<OPTION VALUE="3">Item 3</OPTION>
</SELECT>
<P> Optional <BR>
<INPUT TYPE="TEXT" NAME="optional" SIZE="20">
123
11 - JSP
<P> String (subBean) <BR>
<INPUT TYPE="TEXT" NAME="subBean.string" SIZE="20">
<P> Number (subBean) <BR>
<INPUT TYPE="TEXT" NAME="subBean.number" SIZE="20">
<P>
<INPUT TYPE="SUBMIT" VALUE="Submit">
<INPUT TYPE="RESET" VALUE="Reset">
</FORM>
</BODY>
</HTML>
11.18.3 bean resources
The SimpleBeanResources class is a resource bundle containing optional information that is
useful to the mapping process: default values, error messages, the list of optional properties, the
processing order, the form's name and the processor's name.
The default values are defined for a String, a float, a boolean and an int[]. The primitive values
must be wrapped by a Float and a Boolean in order to be stored as resources. The default values
for the properties of the contained bean could have been defined in another resource bundle
called SimpleSubBeanResources.
There are three error messages. Their role is to help the users to correct the input errors. The
mapping framework contains default error messages for each type of form element.
The list of optional properties has a single element. No error is signaled if the user doesn't
provide a value for this property.
The processing order isn't necessary to this example. It has been included here just for
demonstrative purposes.
The form's name and the processor's name are used by the JSP handler described in the next
section. These two resources aren't accessed by the mapping utilities.
SimpleBeanResources.java:
package com.devsphere.examples.mapping.simple;
{
public class SimpleBeanResources extends java.util.ListResourceBundle
private static final Object[][] contents = {
{ "[DEFAULT_VALUE.string]", "abc" },
{ "[DEFAULT_VALUE.number]", new Float(0.123) },
{ "[DEFAULT_VALUE.flag]", new Boolean(true) },
{ "[DEFAULT_VALUE.list]", new int[] { 2, 3 } },
{ "[ERROR_MESSAGE.integer]", "An option must be selected" },
{ "[ERROR_MESSAGE.colors]", "One or more colors must be
selected" },
{ "[ERROR_MESSAGE.list]", "One or more items must be selected"
},
{
"[OPTIONAL_PROPERTIES]",
new String[] {
124
11 - JSP
"optional"
}
},
{
"[PROCESSING_ORDER]",
new String[] {
"string",
"number",
"integer",
"flag",
"colors",
"list",
"optional",
"subBean"
}
},
{ "[FORM_NAME]", "SimpleForm.html" },
{ "[PROC_NAME]", "SimpleProc.jsp" }
};
public Object[][] getContents() {
return contents;
}
}
11.18.4 JSP Handler
The SimpleHndl.jsp handler is based on a template that was described in a previous chapter.
The formToBean() method of com.devsphere.mapping.FormUtils sets the bean properties to
the values of the request parameters (form data). If necessary, string values are converted to
numbers. A boolean property is set to true if the request parameter is present no matter what its
value is (except "false"). The error messages that occur during the mapping process are stored in
a Hashtable.
The beanToForm() method of com.devsphere.mapping.FormUtils inserts the bean data and the
error messages into the HTML form. It inserts a VALUE attribute for text elements, a CHECKED
attribute for checkboxes and radio buttons that must be selected and a SELECTED attribute for
the list items that must be highlighted.
For a better understanding of this example, a later section of this chapter lists two JSPs that
perform the mapping and build the HTML form without using the framework.
SimpleHndl.jsp:
<%@ page language="java" %>
<%@ page import="com.devsphere.mapping.*, com.devsphere.logging.*" %>
<jsp:useBean id="simpleBean" scope="request"
class="com.devsphere.examples.mapping.simple.SimpleBean"/>
<%
// Get the bean resources
java.util.ResourceBundle beanRes
125
11 - JSP
= HandlerUtils.getBeanResources(simpleBean.getClass());
// Construct the base path
String basePath = request.getServletPath();
int slashIndex = basePath.lastIndexOf('/');
basePath = slashIndex != -1 ? basePath.substring(0,
slashIndex+1) : "";
// Determine the HTTP method
boolean isPostMethod = request.getMethod().equals("POST");
// Create a logger that wraps the servlet context
ServletLogger logger = new ServletLogger(application);
// Wrap the form data
FormData formData = new ServletFormData(request);
// Form-to-bean mapping: request parameters are mapped to bean
properties
java.util.Hashtable errorTable
= FormUtils.formToBean(formData, simpleBean, logger);
if (isPostMethod && errorTable == null) {
// Construct the processor's path
String procPath = basePath +
beanRes.getString("[PROC_NAME]").trim();
// Process the valid data bean instance
application.getRequestDispatcher(procPath).forward(request,
response);
} else {
if (!isPostMethod)
// Ignore the user errors if the form is requested with
GET.
errorTable = HandlerUtils.removeUserErrors(errorTable);
// Construct the form's path
String formPath = basePath +
beanRes.getString("[FORM_NAME]").trim();
formPath = application.getRealPath(formPath);
// Get the form template
FormTemplate template = FormUtils.getTemplate(new
java.io.File(formPath));
// Get a new document
FormDocument document = template.getDocument();
126
11 - JSP
elements
logger);
// Bean-to-form mapping: bean properties are mapped to form
FormUtils.beanToForm(simpleBean, errorTable, document,
// Send the form document
document.send(out);
}
%>
11.18.5 JSP Processor
The SimpleProc.jsp processor gets the beans that were validated by the JSP handler and prints
the values of their properties.
SimpleProc.jsp:
<%@ page language="java"%>
<jsp:useBean id="simpleBean" scope="request"
class="com.devsphere.examples.mapping.simple.SimpleBean"/>
<HTML>
<HEAD><TITLE>Simple bean</TITLE></HEAD>
<BODY>
<H3>Simple Example</H3>
<P><B> SimpleBean properties: </B>
<P> string = <jsp:getProperty name="simpleBean"
property="string"/>
<P> number = <jsp:getProperty name="simpleBean"
property="number"/>
<P> integer = <jsp:getProperty name="simpleBean"
property="integer"/>
<P> flag = <jsp:getProperty name="simpleBean" property="flag"/>
<P> colors = <%= toString(simpleBean.getColors()) %>
<P> list = <%= toString(simpleBean.getList()) %>
<P> optional = <jsp:getProperty name="simpleBean"
property="optional"/>
<P> subBean.string = <%= simpleBean.getSubBean().getString() %>
<P> subBean.number = <%= simpleBean.getSubBean().getNumber() %>
</BODY>
</HTML>
<%!
public static String toString(String list[]) {
if (list == null || list.length == 0)
return "";
if (list.length == 1 && list[0] != null)
return list[0];
StringBuffer strbuf = new StringBuffer();
strbuf.append("{ ");
for (int i = 0; i < list.length; i++)
127
11 - JSP
if (list[i] != null) {
strbuf.append(list[i]);
strbuf.append(" ");
}
strbuf.append("}");
return strbuf.toString();
}
public static String toString(int list[]) {
if (list == null || list.length == 0)
return "";
if (list.length == 1)
return Integer.toString(list[0]);
StringBuffer strbuf = new StringBuffer();
strbuf.append("{ ");
for (int i = 0; i < list.length; i++) {
strbuf.append(list[i]);
strbuf.append(" ");
}
strbuf.append("}");
return strbuf.toString();
}
%>
11.18.6 without using the devsphere framework
ComplexForm.jsp generates the HTML form dynamically and inserts default values and error
messages. It uses 120 lines of Java-JSP-HTML mixture to generate a 40 lines HTML form. A
single call to FormUtils.beanToForm() can do the same using a pure HTML file. In addition,
beanToForm() handles and logs many types of application errors, making the testing and the
debugging easier.
ComplexHndl.jsp uses 150 lines of Java-JSP mixture to set the properties of a bean object to
the values of the request parameters. This is the equivalent of a single FormUtils.formToBean()
call.
The adding/removing of a bean property requires changes in both Complex*.jsp files. Using the
framework, you only have to add/remove a form element to/from a pure HTML file.
The localization of the Complex*.jsp files to other languages requires a lot of work and could
make the maintenance very hard. Using the framework you separate the HTML code from the
Java/JSP code. In addition, default values and error messages are kept in localizable resource
bundles. A later chapter shows how to build internationalized applications using the framework.
ComplexForm.jsp:
<%@ page language="java" %>
<jsp:useBean id="simpleBean" scope="request"
class="com.devsphere.examples.mapping.simple.SimpleBean"/>
<jsp:useBean id="errorTable" scope="request"
class="java.util.Hashtable"/>
<HTML>
<HEAD><TITLE>Without using the framework</TITLE></HEAD>
128
11 - JSP
<BODY>
<H3>Equivalent of Simple Example</H3>
<FORM METHOD=POST>
<P> String <BR>
<%= getErrorMessage(errorTable, "string") %>
<INPUT TYPE="TEXT" NAME="string"
VALUE="<jsp:getProperty name="simpleBean" property="string"/>">
<P> Number <BR>
<%= getErrorMessage(errorTable, "number") %>
<INPUT TYPE="TEXT" NAME="number"
VALUE="<jsp:getProperty name="simpleBean" property="number"/>">
<P> Integer <BR>
<%= getErrorMessage(errorTable, "integer") %>
<%
String integerLabels[] = { "Option 1", "Option 2", "Option 3" };
for (int i = 0; i < integerLabels.length; i++) {
int value = i+1;
boolean checked = simpleBean.getInteger() == value;
%>
<INPUT TYPE="RADIO" NAME="integer" VALUE="<%= value %>"
<%= checked ? "CHECKED" : "" %>> <%= integerLabels[i] %>
<%
}
%>
<P> Flag <BR>
<%= getErrorMessage(errorTable, "flag") %>
<INPUT TYPE="CHECKBOX" NAME="flag"
<%= simpleBean.getFlag() ? "CHECKED" : "" %>> Flag
<P> Colors <BR>
<%= getErrorMessage(errorTable, "colors") %>
<%
String colors[] = simpleBean.getColors();
if (colors == null)
colors = new String[0];
String colorLabels[] = { "Red", "Green", "Blue" };
String colorValues[] = { "red", "green", "blue" };
for (int i = 0; i < colorValues.length; i++) {
boolean checked = false;
if (colors != null)
for (int j = 0; j < colors.length; j++)
if (colors[j].equals(colorValues[i])) {
checked = true;
129
11 - JSP
break;
}
%>
<INPUT TYPE="CHECKBOX" NAME="colors" VALUE="<%= colorValues[i]
%>"
<%= checked ? "CHECKED" : "" %>> <%= colorLabels[i] %>
<%
}
%>
<P> List <BR>
<%= getErrorMessage(errorTable, "list") %>
<SELECT NAME="list" SIZE="3" MULTIPLE>
<%
int list[] = simpleBean.getList();
if (list == null)
list = new int[0];
String listItems[] = { "Item 1", "Item 2", "Item 3" };
for (int i = 0; i < listItems.length; i++) {
int value = i+1;
boolean selected = false;
if (list != null)
for (int j = 0; j < list.length; j++)
if (list[j] == value) {
selected = true;
break;
}
%>
<OPTION VALUE = "<%= value %>"
<%= selected ? "SELECTED" : "" %>> <%= listItems[i] %>
<%
}
%>
</SELECT>
<P> Optional <BR>
<%= getErrorMessage(errorTable, "optional") %>
<INPUT TYPE="TEXT" NAME="optional"
VALUE="<jsp:getProperty name="simpleBean" property="optional"/>">
<% if (simpleBean.getSubBean() == null) simpleBean.setSubBean(
new com.devsphere.examples.mapping.simple.SimpleSubBean()); %>
<P> String (subBean) <BR>
<%= getErrorMessage(errorTable, "subBean.string") %>
<INPUT TYPE="TEXT" NAME="subBean.string"
VALUE="<%= simpleBean.getSubBean().getString() %>">
130
11 - JSP
<P> Number (subBean) <BR>
<%= getErrorMessage(errorTable, "subBean.number") %>
<INPUT TYPE="TEXT" NAME="subBean.number"
VALUE="<%= simpleBean.getSubBean().getNumber() %>">
<P>
<INPUT TYPE="SUBMIT" VALUE="Submit">
<INPUT TYPE="RESET" VALUE="Reset">
</FORM>
</BODY>
</HTML>
<%!
String getErrorMessage(java.util.Hashtable errorTable, String
property) {
String message = (String) errorTable.get(property);
if (message == null)
message = "";
return message;
}
%>
ComplexHndl.jsp:
<%@ page language="java" %>
<jsp:useBean id="simpleBean" scope="request"
class="com.devsphere.examples.mapping.simple.SimpleBean"/>
<jsp:useBean id="simpleSubBean" scope="page"
class="com.devsphere.examples.mapping.simple.SimpleSubBean"/>
<jsp:useBean id="errorTable" scope="request"
class="java.util.Hashtable"/>
<%
simpleBean.setSubBean(simpleSubBean);
boolean isPostMethod = request.getMethod().equals("POST");
if (isPostMethod) {
//* string : text
%>
<jsp:setProperty name="simpleBean" property="string"/>
<%
if (simpleBean.getString() == null
|| simpleBean.getString().length() == 0) {
simpleBean.setString("abc");
131
11 - JSP
setErrorMessage(errorTable, "string", "Must be filled");
}
//* number : text
try {
String numberValue = request.getParameter("number");
if (numberValue != null && numberValue.length() != 0)
simpleBean.setNumber(new
Float(numberValue).floatValue());
else {
simpleBean.setNumber(0.123f);
setErrorMessage(errorTable, "number", "Must be
filled");
}
} catch (NumberFormatException e) {
simpleBean.setNumber(0.123f);
setErrorMessage(errorTable, "number", "Must be a number");
}
//* integer : radio group
%>
<jsp:setProperty name="simpleBean" property="integer"/>
<%
if (simpleBean.getInteger() == 0) {
setErrorMessage(errorTable, "integer", "An option must be
selected");
}
//* flag : checkbox
String flagValue = request.getParameter("flag");
if (flagValue != null) {
flagValue = flagValue.trim();
if (flagValue.length() == 0 || flagValue.equals("false"))
flagValue = null;
}
simpleBean.setFlag(flagValue != null);
//* color : checkbox group
%>
<jsp:setProperty name="simpleBean" property="colors"/>
<%
if (simpleBean.getColors() == null
|| simpleBean.getColors().length == 0) {
132
11 - JSP
setErrorMessage(errorTable, "colors",
"One or more colors must be selected");
}
//* list : select
%>
<jsp:setProperty name="simpleBean" property="list"/>
<%
if (simpleBean.getList() == null
|| simpleBean.getList().length == 0) {
simpleBean.setList(new int[] { 2, 3 });
setErrorMessage(errorTable, "list",
"One or more items must be selected");
}
//* optional : text
%>
<jsp:setProperty name="simpleBean" property="optional"/>
<%
if (simpleBean.getOptional() == null)
simpleBean.setOptional("");
//* subBean.string : text
%>
<jsp:setProperty name="simpleSubBean" property="string"
param="subBean.string"/>
<%
filled");
if (simpleSubBean.getString() == null
|| simpleSubBean.getString().length() == 0) {
simpleSubBean.setString("");
setErrorMessage(errorTable, "subBean.string", "Must be
}
//* subBean.number : text
try {
String numberValue =
request.getParameter("subBean.number");
if (numberValue != null && numberValue.length() != 0)
simpleSubBean.setNumber(new
Float(numberValue).floatValue());
else {
setErrorMessage(errorTable, "subBean.number", "Must be
133
11 - JSP
filled");
number");
}
} catch (NumberFormatException e) {
setErrorMessage(errorTable, "subBean.number", "Must be a
}
} else {
simpleBean.setString("abc");
simpleBean.setNumber(0.123f);
simpleBean.setFlag(true);
simpleBean.setList(new int[] { 2, 3 });
simpleBean.setOptional("");
simpleSubBean.setString("");
}
if (isPostMethod && errorTable.isEmpty()) {
%>
<jsp:forward page="SimpleProc.jsp"/>
<%
} else {
%>
<jsp:forward page="ComplexForm.jsp"/>
<%
}
%>
<%!
void setErrorMessage(java.util.Hashtable errorTable,
String property, String message) {
message = "<FONT COLOR=\"#FF0000\">" + message +
"</FONT><BR>";
errorTable.put(property, message);
}
%>
11.18.7 using the framework with servlets and JSPs
The SimpleHndl.jsp handler is basically a Java scriptlet. That was a simple and compact way to
present a handler. The Java code could easily be moved to a utility class. A more elegant solution
is the replacement of the JSP handler with a general Java servlet.
The com.devsphere.helpers.mapping package contains an abstract class called
GenericHandler. This class is extended by BeanDispatcher, which is the bean-independent
equivalent of SimpleHndl.jsp. The JSP handler can be replaced by only a few lines that are added
to servlets.properties or web.xml:
SimpleHndl.code=com.devsphere.helpers.mapping.BeanDispatcher
SimpleHndl.initparams=\
BEAN_NAME=com.devsphere.examples.mapping.simple.SimpleBean,\
134
11 - JSP
BEAN_ID=simpleBean,\
BASE_PATH=/simple
or
<servlet>
<servlet-name>SimpleHndl</servlet-name>
<servletclass>com.devsphere.helpers.mapping.BeanDispatcher</servlet-class>
<init-param>
<param-name>BEAN_NAME</param-name>
<paramvalue>com.devsphere.examples.mapping.simple.SimpleBean</param-value>
</init-param>
<init-param>
<param-name>BEAN_ID</param-name>
<param-value>simpleBean</param-value>
</init-param>
<init-param>
<param-name>BASE_PATH</param-name>
<param-value>/simple</param-value>
</init-param>
</servlet>
GenericHandler and BeanDispatcher were presented in a previous chapter.
11.18.8 why using servlets?
Using a JSP, you have to declare the bean within a <jsp:useBean> tag. If your Web application
contains many forms/beans, you have to provide a JSP handler for each bean. A servlet can be
made bean-independent.
In many cases, a servlet is identified with its class. Users invoke the servlet by requesting a
URL like this:
http://www.host.com/AppName/servlet/ServletName
The servlet engine associates a servlet to a class in the servlets.properties (or web.xml) file:
ServletName.code=com.company.ClassName
There is nothing that can stop you associating many servlets with the same class. You may use
the same class to declare one servlet for each bean component. A standard servlet engine
running on a single JVM will instantiate the servlet class once for each servlet declaration. All
requests to one of the declared servlets will be serviced by the same instance of the servlet class.
The previous section showed how to declare a BeanDispatcher servlet. If you have another
bean-form pair, you could add a few other lines to servlets.properties:
AnotherHndl.code=com.devsphere.helpers.mapping.BeanDispatcher
AnotherHndl.initparams=\
BEAN_NAME=com.devsphere.examples.mapping.another.AnotherBean,\
BEAN_ID=anotherBean,\
BASE_PATH=/another
The two servlets that share the same code could be invoked with something like this
http://www.host.com/AppName/servlet/SimpleHndl
http://www.host.com/AppName/servlet/AnotherHndl
135
12 - javaserver faces
12 - JAVASERVER FACES
12.1 what are javaServer faces?
JavaServer Faces technology is a server-side user interface component framework for Java
based web applications. This technology includes:
1. A set of APIs for:
•
representing UI components, like input fields, buttons, links
•
UI components management
•
events handling
•
input validation
•
error handling
•
page navigation specification
•
support for internationalization and accessibility.
2. A JavaServer Pages (JSP) custom tag library for expressing a JavaServer Faces
interface within a JSP page.
JSF is a request-driven MVC web framework based on component driven UI design model,
using XML files called view templates or Facelets views. Requests are processed by the
FacesServlet, which loads the appropriate view template, builds a component tree, processes
events, and renders the response (typically HTML) to the client.
12.2 javaServer Faces Technology 2.0
The latest version (as of november 2010) of JavaServer Faces technology is version 2.0,
released through the Java Community Process under Java Specification Request (JSR) 314.
Version 2.0 is part of the Java Enterprise Edition 6 platform.
Version 2.0 supersedes version 1.2 and brings in mandatory support for Facelets as the view
technology for JSF pages, built in Ajax support and built in support for bookmarking & page-load
actions.
There are five JSF specific tag libraries defined in this specification, namely
•
JSF HTML Tag Library
•
JSF Core Tag Library
•
JSTL Core Tag Library
•
JSTL Functions Tag Library
•
JSF Facelets Tag Library
136
12 - javaserver faces
12.3 facelets
Facelet is a view technology for Java Server Faces (JSF) that allows building composite views
more quickly and easily than with JSP which is the default view technology for JSF. JSP pages
are compiled into servlets but it’s not the case with Facelets because Facelet pages are XML
compliant and its framework uses a fast SAXbased compiler to build views. Facelets can make
changes to pages immediately so developing JSF applications with Facelets is simply faster.
12.4 the html JSF tags
This tag library contains JavaServer Faces component tags for all UIComponent + HTML
RenderKit Renderer combinations defined in the JavaServer Faces specification. As of version
1.2 of the JFS specification, there are 25 HTML JSF tags.
The HTML tags can be grouped in the following categories:
•
inputs
•
outputs
•
commands
•
selections
•
layouts
•
data table
•
errors and messages
12.4.1 the list of JSF HTML Tags
For reference, here is an exhaustive list of the JSF HTML tags:
•
column
•
commandButton
•
commandLink
•
dataTable
•
form
•
graphicImage
•
inputHidden
•
inputSecret
•
inputText
•
inputTextArea
•
message
•
messages
•
outputFormat
137
12 - javaserver faces
•
outputLabel
•
outputLink
•
outputText
•
panelGrid
•
pnelGroup
•
selectBooleanCheckbox
•
selectManyCheckbox
•
selectManyListbox
•
selectManyMenu
•
selectOneListbox
•
selectOneMenu
•
selectOneRadio
In the next paragraphs, we'll have a closer look at some of these tags.
12.4.2 h:dataTable
The dataTable tag renders an HTML 4.01 compliant table element that can be associated with
a backing bean to obtain its data as well as for event handling purposes.
The table can be customized extensively using cascading stylesheet (CSS) classes and
definitions to enhance the appearance of the table's headers, footers, columns and rows.
Common formatting techniques, such as alternating row colors, can be accomplished quite easily
with this tag.
The dataTable tag typically contains one or more column tags that define the columns of the
table. A column component is rendered as a single "td" element. For more information about
columns, see the column tag documentation.
A dataTable tag can also contain header and footer facets. These are rendered as a single "th"
element in a row at the top of the table and as a single "td" element in a row at the bottom of the
table, respectively.
Example:
<h:dataTable id="table1" value="#{shoppingCartBean.items}" var="item">
<f:facet name="header">
<h:outputText value="Your Shopping Cart" />
</f:facet>
<h:column>
<f:facet name="header">
<h:outputText value="Item Description" />
</f:facet>
<h:outputText value="#{item.description}" />
</h:column>
<h:column>
<f:facet name="header">
<h:outputText value="Price" />
138
12 - javaserver faces
</f:facet>
<h:outputText value="#{item.price}" />
</h:column>
<f:facet name="footer">
<h:outputText value="Total: #{shoppingCartBean.total}" />
</f:facet>
</h:dataTable>
HTML Output
<table id="table1">
<thead>
<tr><th scope="colgroup" colspan="2">Your Shopping Cart</th></tr>
<tr><th>Item Description</th><th>Price</th></tr>
</thead>
<tbody>
<tr><td>Delicious Apple</td><td>$5.00</td></tr>
<tr><td>Juicy Orange</td><td>$5.00</td></tr>
<tr><td>Tasty Melon</td><td>$5.00</td></tr>
</tbody>
<tfoot>
<tr><td colspan="2">Total: $15.00</td></tr>
</tfoot>
</table>
12.4.3 h:form
The form tag renders an HTML form element. JSF forms use the "post-back" technique to
submit form data back to the page that contains the form. The use of the POST method is also
required and it is not possible to use the GET method for forms generated by this tag.
If your application requires the use of the GET method for form submission, your options
include using plain HTML forms, binding request parameters to backing bean properties, and
using the outputLink tag to generate dynamic hyperlinks.
Example:
<h:form id="form1"></h:form>
HTML Output
<form id="form1" name="form1" method="post" action="/demo/form.jsp"
enctype="application/x-www-form-urlencoded"></form>
12.4.4 h:commandButton
The commandButton tag renders an HTML submit button that can be associated with a
backing bean or ActionListener class for event handling purposes. The display value of the button
can also be obtained from a message bundle to support internationalization (I18N).
Example:
<h:commandButton id="button1" value="#{bundle.checkoutLabel}"
action="#{shoppingCartBean.checkout}" />
139
12 - javaserver faces
HTML Output
<input id="form:button1" name="form:button1" type="submit"
value="Check Out" onclick="someEvent();" />
12.4.5 h:inputText
The inputText tag renders an HTML input element of the type "text".
Example:
<h:inputText id="username" value="#{userBean.user.username}" />
HTML Output
<input id="form:username" name="form:username" type="text" />
12.4.6 message Tag
The message tag renders a message for a specific component. You can customize the
message generated by this component by applying different CSS styles to the message
depending on its severity (eg. red for error, green for information) as well as the detail level of the
message itself. You can also customize the standard error messages by overriding specific JSF
properties in your message bundle.
Example:
<h:inputText id="username" required="#{true}"
value="#{userBean.user.username}"
errorStyle="color:red"/>
<h:message for="username" />
HTML Output
<input type="text" id="form:username" name="form:username" value=""/>
<span style="color:red">"username": Value is required.</span>
12.5 the core JSF tags
The core JavaServer Faces tags define custom actions that are independent of any particular
RenderKit.
12.5.1 the list of JSF Core Tags
Here is an exhaustive list of the JSF core tags:
•
actionListener
•
attribute
•
convertDateTime
•
converter
•
convertNumber
•
facet
140
12 - javaserver faces
•
loadBundle
•
param
•
selectItem
•
selectItems
•
subview
•
validateDoubleRange
•
validateLength
•
validateLongRange
•
validator
•
valueChangeListener
•
verbatim
•
view
Some of these tags will be detailed in the next paragraphs.
12.5.2 f:facet
A facet represents a named section within a container component
The JSF facets specify the requirements and constraints that apply to a JSF project.
The Facet tag registers a named facet on the component associated with the enclosing tag. For
example, you can create a header and a footer facet for a dataTable component.
Example:
<h:dataTable id="reportTable" value="#{reportBean.dailyReport}"
var="item">
<h:column>
<f:facet name="header">
<h:outputText value="Daily Report" />
</f:facet>
<h:outputText value="#{item}" />
</h:column>
</h:dataTable>
HTML Output
<table id="reportTable">
<thead>
<tr><th>Daily Report</th></tr>
</thead>
<tbody>
<tr><td>Item 1</td></tr>
<tr><td>Item 2</td></tr>
<tr><td>Item 3</td></tr>
</tbody>
</table>
141
12 - javaserver faces
12.5.3 f:validator
The Validator tag registers a named Validator instance on the component associated with the
enclosing tag. The JavaServer Faces framework includes three standard validators (see the
validateDoubleRange, validateLength, and validateLongRange tags) but the Validator interface
can be implemented by classes that provide custom validation for your application. This tag
accepts one value matching the validator ID you assigned to your validator class in your Faces
configuration file. The body content of this tag must be empty.
Example:
<h:inputText id="emailAddress"
value="#{customerBean.customer.emailAddress}">
<f:validator validatorId="emailAddressValidator" />
</h:inputText>
<h:message for="emailAddress" />
HTML Output
<input id="form:emailAddress" name="form:emailAddress" type="text"
value="fake@email"/>
Invalid email address.
12.5.4 f:valueChangeListener
The ValueChangeListener tag registers a ValueChangeListener instance on the component
associated with the enclosing tag. The ValueChangeListener interface should be implemented by
classes that you want to register with components that publish value change events.
Any component that receives user input, such as one of the HTML select or text input
components, can publish value change events. A component fires a value change event when its
input changes, but only if the new input is validated successfully.
You can register several ValueChangeListeners with a component and they will be invoked in
the order that they are registered. An alternative to this tag is to use a method-binding expression
pointing at a value change listener method of a backing bean on the component tag itself.
Notice in the example below the use of the JavaScript onchange() event to trigger form
submission when the list selection changes. Without this JavaScript event, the user must
manually submit the form to invoke the ValueChangeListener.
Example:
<h:selectOneMenu id="optionMenu" value="#{optionBean.selectedOption}"
onchange="submit()">
<f:selectItems value="#{optionBean.optionList}" />
<f:valueChangeListener
type="com.mycompany.MyValueChangeListenerImpl" />
</h:selectOneMenu>
HTML Output
<select name="form:optionMenu" size="1" onchange="submit()">
<option value="1">Option 1</option>
<option value="2">Option 2</option>
<option value="3">Option 3</option>
</select>
142
12 - javaserver faces
12.5.5 f:view
The View tag is the container for all JavaServer Faces component tags used on a page. You
can wrap the root element of the structured markup language used in your document with this tag
to ensure that all child tags are part of the same view.
This tag is useful for internationalization (I18N) purposes. It provides you with several options
for presenting your user with localized views of your application. By default the JSF framework
will attempt to select the best view for your user based on the Accept-Language header sent to
the server from the user's browser as part of the HTTP request for your page.
If the locale requested by the user is not supported by your application, the JSF framework will
use the default locale specified in your Faces configuration file. If you have not specified a default
locale, JSF will use the default locale for the Java Virtual Machine serving your application.
If your application supports the locale requested by the user, JSF will set that locale for the view
and will display the messages for that locale defined in the locale's message bundle.
You can also specify the locale for which the view is to be rendered by explicitly setting the
locale attribute of the view tag. This allows you to design localized versions of each page,
including images and styles, for each locale you wish to support.
Another option is to obtain the locale dynamically through user interaction. This information
could later be stored in a cookie and/or a database to identify which locale is preferred by your
user. The locale attribute accepts a value-binding expression that could resolve to the desired
locale.
Example:
welcome_en.jsp (English)
<f:view locale="en">
<f:loadBundle basename="com.mycompany.MessageBundle" var="bundle" />
<h:outputText value="#{bundle.welcomeMessage}" />
</f:view>
welcome_fr.jsp (French)
<f:view locale="fr">
<f:loadBundle basename="com.mycompany.MessageBundle" var="bundle" />
<h:outputText value="#{bundle.welcomeMessage}" />
</f:view>
HTML Output
welcome_en.jsp (English)
Welcome to our site!
welcome_fr.jsp (French)
Bienvenue à notre site!
12.6 the structure of a JSF application
Here is a typical directory structure for a JSP application. The directory myJSFapp is the base
directory of the application.
myJSFapp
143
12 - javaserver faces
/ant
build.xml
/JavaSource
/WebContent
/WEB-INF
/classes
/lib
jsf-impl.jar
jsf-api.jar
faces-config.xml
web.xml
/pages
Comments on this structure:
•
myJSFapp – application base directory with application name
•
/ant – directory containing Ant build scripts with a default build.xml file
•
/JavaSource – application specific java source classes and properties files
•
/WebContent – contains the Web application files used by the application server or by
the web container
•
/WEB-INF – contains files used as part of the runtime Web application
•
/classes – compiled Java classes and properties files copied from the /JavaSource
directory
•
/lib - contains libraries required by the application, like third party jar files
•
jsf-impl.jar, jsf-api.jar – files included in the /lib directory, mandatory for any JSF
application
•
web.xml – the deployment descriptor of the application, included in the /WEB-INF
directory
•
faces-config.xml – the JSF configuration file, included in the /WEB-INF directory
•
/pages – directory containing JSP and HTML presentation pages
12.7 how does JSF work? a first example
Example taken from http://www.exadel.com/tutorial/jsf/jsftutorial-kickstart.html.
A JSF application is nothing else but a servlet/JSP application. It has a deployment descriptor,
JSP pages, custom tag libraries, static resources, and so on. What makes it different is that a JSF
application is event-driven. The way the application behaves is controlled by an event listener
class. Let's have a look at the steps needed to build a JSF application:
1. Create JSP pages
2. Define navigation rules
3. Create managed beans
4. Create properties files
144
12 - javaserver faces
5. Edit JSP pages
6. Create an index.jsp file
7. Compile the application
8. Deploy and run the application
12.7.1 creating JSP Pages
Create the inputname.jsp and greeting.jsp files in WebContent/pages/. You only need to
create the JSP files. The directory structure already exists.
These files will act as place holders for now. We will complete the content of the files a little bit
later.
Now that we have the two JSP pages, we can create a navigation rule.
12.7.2 navigation
Navigation is the heart of JavaServer Faces. The navigation rule for this application is
described in the faces-config.xml file. This file already exists in the skeleton directory structure.
You just need to create its contents.
In our application, we just want to go from inputname.jsp to greeting.jsp. As a diagram, it
would look something like this:
Image from Exadel Studio Pro
The navigation rule shown in the picture is defined below. The rule says that from the view
(page) inputname.jsp go to the view (page) greeting.jsp, if the "outcome" of executing
inputname.jsp is greeting. And that's all there is to this.
<navigation-rule>
<from-view-id>/pages/inputname.jsp</from-view-id>
<navigation-case>
<from-outcome>greeting</from-outcome>
<to-view-id>/pages/greeting.jsp</to-view-id>
</navigation-case>
</navigation-rule>
145
12 - javaserver faces
This is, of course, a very simple navigation rule. You can easily create more complex ones. To
read more about navigation rules, visit the JSP Navigation Example forum item.
12.7.3 creating the Managed Bean
Next, we will create a myJFSapp folder inside the JavaSource folder. Inside this myJFSapp
folder, we will create a PersonBean.java file. This class is straight-forward. It's a simple Java
bean with one attribute and setter/getter methods. The bean simply captures the name entered by
a user after the user clicks the submit button. This way the bean provides a bridge between the
JSP page and the application logic. (Please note that the field name in the JSP file must exactly
match the attribute name in the bean.)
12.7.3.1 PersonBean.java
Put this code in the file:
package myJFSapp;
public class PersonBean {
String personName;
/**
* @return Person Name
*/
public String getPersonName() {
return personName;
}
/**
* @param Person Name
*/
public void setPersonName(String name) {
personName = name;
}
}
Later you will see how to "connect" this bean with the JSP page.
12.7.3.2 declaring the Bean in faces-config.xml
Now, the second part of faces-config.xml describes our Java bean that we created in the
previous steps. This section defines a bean name PersonBean. The next line is the full class
name, myJFSapp.PersonBean. request sets the bean scope in the application.
<managed-bean>
<managed-bean-name>personBean</managed-bean-name>
<managed-bean-class>myJFSapp.PersonBean</managed-bean-class>
<managed-bean-scope>request</managed-bean-scope>
</managed-bean>
12.7.3.3 faces-config.xml
Your final faces-config.xml file should look like this:
146
12 - javaserver faces
<?xml version="1.0"?>
<!DOCTYPE faces-config PUBLIC
"-//Sun Microsystems, Inc.//DTD JavaServer Faces Config 1.1//EN"
"http://java.sun.com/dtd/web-facesconfig_1_1.dtd">
<faces-config>
<navigation-rule>
<from-view-id>/pages/inputname.jsp</from-view-id>
<navigation-case>
<from-outcome>greeting</from-outcome>
<to-view-id>/pages/greeting.jsp</to-view-id>
</navigation-case>
</navigation-rule>
<managed-bean>
<managed-bean-name>personBean</managed-bean-name>
<managed-bean-class>myJFSapp.PersonBean</managed-bean-class>
<managed-bean-scope>request</managed-bean-scope>
</managed-bean>
</faces-config>
12.7.4 creating a Properties File (Resource Bundle)
A properties file is just a file with param=value pairs. We use the messages stored in the
properties file in our JSP pages. Keeping the messages separate from the JSP page allows us to
quickly modify the messages without editing the JSP page.
Let's create a bundle folder in the JavaSource/myJFSapp folder and then a
messages.properties file in the bundle folder. We need to place it in the JavaSource folder so
that during project compilation, this properties file will be copied to the classes folder where the
runtime can find it.
12.7.4.1 messages.properties
Put this text in the properties file:
inputname_header=JSF KickStart
prompt=Tell us your name:
greeting_text=Welcome to JSF
button_text=Say Hello
sign=!
We now have everything to create the JSP pages.
12.7.5 editing the JSP Pages
Two pages should already have been created in myJFSapp/WebContent/pages.
12.7.5.1 inputname.jsp
Put the following coding into this file:
<%@ taglib uri="http://java.sun.com/jsf/html" prefix="h" %>
<%@ taglib uri="http://java.sun.com/jsf/core" prefix="f" %>
147
12 - javaserver faces
<f:loadBundle basename="myJFSapp.bundle.messages" var="msg"/>
<html>
<head>
<title>enter your name page</title>
</head>
<body>
<f:view>
<h1>
<h:outputText value="#{msg.inputname_header}"/>
</h1>
<h:form id="helloForm">
<h:outputText value="#{msg.prompt}"/>
<h:inputText value="#{personBean.personName}" required=”true”>
<f:validateLength minimum="2" maximum="10"/>
</h:inputText>
<h:commandButton action="greeting" value="#{msg.button_text}" />
</h:form>
</f:view>
</body>
</html>
Now, let's explain the important sections in this file after displaying the code for each section
starting from the top.
<%@ taglib uri="http://java.sun.com/jsf/html" prefix="h" %>
<%@ taglib uri="http://java.sun.com/jsf/core" prefix="f" %>
<f:loadBundle basename="myJFSapp.bundle.messages" var="msg"/>
The first line of these three is a directive that tells us where to find JSF tags that define HTML
elements and the second directive tells us where to find JSF tags that define core JSF elements.
The third line loads our properties file (resource bundle) that holds messages that we want to
display in our JSP page.
<h:inputText value="#{msg.inputname_header}" required=”true”>
This tag simply tells us to look in the resource bundle that we defined at the top of the page.
The required attribute of the h:inputText tag insures that an empty name will not be sent. One
can also add a line like
<f:validateLength minimum="2" maximum="10"/>
to make sure that the length of this field is reasonable long.
Then, look up the value for inputname_header in that file and print it here.
1 <h:form id="helloForm">
2
<h:outputText value="#{msg.prompt}"/>
3
<h:inputText value="#{personBean.personName}" required=”true”>
4
<f:validateLength minimum="2" maximum="10"/>
5
</h:inputText>
6
<h:commandButton action="greeting" value="#{msg.button_text}" />
7 </h:form>
148
12 - javaserver faces
Line 1. Creates an HTML form using JSF tags.
Line 2. Prints a message from the properties file using the value of prompt.
Lines 3-5. Creates an HTML input text box. In the value attribute we connect (bind) this field to
the managed bean attribute that we created before.
Line 6. JSF tags for the HTML form's submit button. The button's value is being retrieved from
the properties file. While the button's action attribute is set to greeting which matches the
navigation-outcome in faces-config.xml file. That's how JSF knows where to go next.
12.7.5.2 greeting.jsp
Put this coding inside the second JSP file:
<%@ taglib uri="http://java.sun.com/jsf/html" prefix="h" %>
<%@ taglib uri="http://java.sun.com/jsf/core" prefix="f" %>
<f:loadBundle basename="myJFSapp.bundle.messages" var="msg"/>
<html>
<head>
<title>greeting page</title>
</head>
<body>
<f:view>
<h3>
<h:outputText value="#{msg.greeting_text}" />,
<h:outputText value="#{personBean.personName}" />
<h:outputText value="#{msg.sign}" />
</h3>
</f:view>
</body>
</html>
This page is very simple. The first three lines are identical to our first page. Theses lines import
JSF tag libraries and our properties file (resource bundle) with the messages.
The main code of interest to us is between the <h3>...</h3> tags. The first line will take a
message from the resource bundle and print it on the page. The second line will access a Java
bean, specifically the bean attribute personName, and also print its contents on the page.
Once this page is displayed in a Web browser, you will see something like this:
Welcome to JSF, name!
12.7.6 creating the index.jsp File
We will now create a third JSP file that doesn't actually function as a presentation page. It uses
a JSP tag to "forward" to the inputname.jsp page.
Create the index.jsp file inside the WebContent folder. Note that this file is not created in the
pages folder like the previous JSP files.
Having an index.jsp file will allow us to start the application like this:
http://localhost:8080/myJFSapp/
149
12 - javaserver faces
Now, put this coding into the file:
<html>
<body>
<jsp:forward page="/pages/inputname.jsf" />
</body>
</html>
If you look at the path for the forward, you'll notice the file suffix is .jsf and not .jsp. This is used
here, because in the web.xml file for the application *.jsf is the URL pattern used to signal that
the forwarded page should be handled by the JavaServer Faces servlet within Tomcat.
We are almost done with this example.
12.7.7 Compiling
An Ant build script is provided for you. To build the application run the build.xml script from the
ant folder:
ant build
12.7.8 Deploying
Before you can run this application within the servlet container, we need to deploy it. We will
use null (link) deployment to deploy the application in-place. To do this we need to register a
context in Tomcat's {TomcatHome}\conf\server.xml file.
To do this, insert this code:
<Context debug="0"
docBase="Path_to_WebContent"
path="/myJFSapp" reloadable="true"/>
near the end of the server.xml file within the Host element just before the closing </Host> tag.
Of course, Path_to_WebContent needs to be replaced with the exact path on your system to the
WebContent folder inside the myJFSapp folder (for example,
C:/examples/myJFSapp/WebContent).
12.7.9 Running
Next, start the Tomcat server (probably using the script startup.bat in Tomcat's bin directory).
When Tomcat is done loading, launch a web browser and enter:
http://localhost:8080/myJFSapp. (Port 8080 is the default port in Tomcat. Your setup, though,
might possibly be different).
12.8 creating a JSF application in eclipse with the facesIDE plugin
Example taken from http://amateras.sourceforge.jp/docs/FacesIDE/SampleJSFApp.html .
12.8.1 Overview
This is a tutorial in which we create a simple JSF application to demonstrate FacesIDE's
functionality. This is a "login" application, which asks an user for an ID and password, verifies the
information, and forwards the user to a success or error page.
150
12 - javaserver faces
The application will use a few JSP pages with JSF elements, and a session-scoped managed
bean to coordinate their interactions. Along the way we'll use the following FacesIDE functionality:
•
•
•
•
add JSF support to a project
use the New JSF/JSP file wizard
use the JSP Editor (see HTML/JSP/XML Editor)
use the faces-config.xml Editor (see faces-config.xml Editor)
As a prerequisite for the tutorial, make sure FacesIDE and required plugins have been installed;
see Installing & Uninstalling. We don't assume that a J2EE server-specific plugin, such as the
Sysdeo Tomcat plugin has been installed.
12.8.2 Creating A Project
Here we create an Eclipse project, and set up folders for a web application. The folder structure
created is simply one that works for this author; your mileage may vary.
1. From the menu bar select File/New/Project.... The New Project wizard appears.
2. Select Java Project; click Next.
3. Enter project name, say, jsf-login; click Finish
4. Create the web root folder: in Package Explorer select the jsf-login project, and from
the menubar select File/New/Folder; name the folder webroot
5. Create the web pages folder: in Package Explorer select the webroot folder, and from its
context menu select File/New/Folder; name the folder pages. This folder will contain all
"functional" pages.
6. Use FacesIDE to add JSF support: we use a FacesIDE wizard to create J2EEprescribed folders and files in webroot, and to add JSF libraries to the project.
a. in Package Explorer select the jsf-login project
b. from the menubar select File/New/Other...
c. in the wizard that appears, select Amateras/JSF/Add JSF Support; click Next
d. in the Add JSF Support page, for Web Application Root enter /jsflogin/webroot; make sure all checkboxes are checked; click Next.
7. From the menubar open Project/Properties
8. Select the Amateras node; note that Root: has automatically been set to /webroot;
make sure HTML validation and DTD/XSD validation are enabled.
9. Create the source folder: select the Java Build Path node; select the Source tab; click
Add Folder...; in the dialog that appears create a folder named src directly under the
project folder (jsf-login); click Yes through messages that appear.
10.Set the output folder: in the Default output folder textbox at the bottom, enter jsflogin/webroot/WEB-INF/classes; click OK to dismiss the properties dialog.
Your folder structure should now be as follows:
jsf-login
|
+-- src
|
+-- webroot
|
+-- WEB-INF
151
12 - javaserver faces
|
|
|
+-- classes (not shown in Java perspective)
|
|
|
+-- lib
|
+-- pages
12.8.3 Creating & Configuring Managed Beans
Here we create a class called LoginManager which will be used as a backing bean for the
login process. We then configure it to be a managed bean.
1. In Package Explorer select the src folder; from its context menu select New/Class. The
New Java Class wizard appears.
2. In the Package field, enter login; in the Name field enter LoginManager. Click Finish.
The Java code editor opens.
3. Enter and save the following code for the LoginManager class:
// LoginManager.java
package login;
public class LoginManager {
private String _uid = "";
private String _pwd = "";
public
public
public
public
String getUserID() { return _uid; }
void setUserID(String uid) { _uid = uid; }
String getPassword() { return _pwd; }
void setPassword(String pwd) { _pwd = pwd; }
public String loginAction() {
String action = null;
if ( _uid.equalsIgnoreCase("foo") &&
_pwd.equalsIgnoreCase("bar") )
action = "loginPass";
else
action = "loginFail";
}
}
return action;
4. Use FacesIDE to configure the bean: we use a FacesIDE editor to configure
LoginManager as a session-scoped managed bean.
a. in Package Explorer select jsf-login/webroot/WEB-INF/facesconfig.xml; from its context menu select Open With/faces-config.xml Editor.
The faces-config.xml editor opens.
b. along the bottom of the editor there are 3 tabs; click Managed Bean.
c. click Add; input widgets appear
d. for name enter mgr; for class enter login.LoginManager; for scope select
152
12 - javaserver faces
session.
e. from the menubar select File/Save, then close the editor
12.8.4 Creating JSP Pages
Here we create the JSP pages that make up the application's user interface. We will have 4
pages: a start page (index.jsp), and 3 content pages (login.jsp, success.jsp and
error.jsp). Content pages are placed in webroot/pages; index.jsp is placed directly in
webroot, and its sole function is to forward users to the login page.
All pages except login.jsp are simple pages with static content, so we create them first,
using the Workbench's standard file-creation facilities. Then we create login.jsp using a
FacesIDE wizard.
1. Create index.jsp:
a. in Package Explorer select webroot; from its context menu select New/File; the
New File wizard appears.
b. for File name enter index.jsp; make sure that the parent folder is set to /jsflogin/webroot; click Finish; the JSP Editor opens.
c. enter the following code, save the file and close the editor.
<!-- webroot/index.jsp -->
<html>
<body>
<jsp:forward page="faces/pages/login.jsp" />
</body>
</html>
2. Create success.jsp: create this file similarly to index.jsp, but in webroot/pages.
Enter the following code:
<!-- webroot/pages/success.jsp -->
<html>
<head>
<title>jsf-login</title>
</head>
<body>
<h2>Success!</h2>
</body>
</html>
3. Create error.jsp: create this file similarly to index.jsp, but in webroot/pages.
Enter the following code:
<!-- webroot/pages/error.jsp -->
<html>
<head>
<title>jsf-login</title>
</head>
<body>
<h2>Error!</h2>
The user-id and or password were invalid.
again.
</body>
Please try
153
12 - javaserver faces
</html>
4. Create login.jsp:
a. in Package Explorer select webroot/pages; from its context menu select
New/Other...; the New wizard appears.
b. select Amateras/JSF/Faces JSP File; click Next
c. for File name enter login.jsp; make sure that Container is set to /jsflogin/webroot/pages, and that Use MyFaces Tomahawk components and
Use MyFaces SandBox components are unchecked, and choose default for
Template; click Finish; the FacesIDE JSP Editor opens, with the following
template code.
<%@ page contentType="text/html; charset=Cp1252" %>
<%@ taglib uri="http://java.sun.com/jsf/html" prefix="h" %>
<%@ taglib uri="http://java.sun.com/jsf/core" prefix="f" %>
<html>
<head>
<meta http-equiv="Content-Type" content="text/html;
charset=Cp1252"/>
<title></title>
</head>
<body>
<f:view>
<h:form>
</h:form>
</f:view>
</body>
</html>
We will now edit this page to contain our input widgets, etc.
d. place the cursor between the <title></title> elements; enter jsf-login
e. Open the JSF palette, and dock it along the right. (See Show View Dialog)
f. create a few blank lines between the <h:form> elements; place your cursor in
one of these lines, expand the JSF HTML panel in the palette, and click on the
icon for <h:inputText>; this inserts the corresponding JSF element at the
cursor location.
Note: the JSP editor is aware of referenced tag libraries, and uses them for code
completion as well. Thus if you were to type <h: and hit CTRL + Spacebar, you
would get a popup window of JSF HTML elements.
g. now we want to add attributes to this element, and the JSP Editor can help with
code- completion. To see this in action, place the cursor inside the <h:inputText>
element, and hit CTRL + Spacebar; a code-completion window pops up, as
shown below.
154
12 - javaserver faces
h. in the code-completion window scroll down to value, and hit Enter; this inserts
value="" at the cursor. We will now bind this to the userID property of
LoginManager; FacesIDE can provide code completion here as well.
i. place the cursor between the quotes in value="", enter #{mgr., and hit CTRL +
Spacebar; a code-completion window pops up, with bean properties available in
mgr. This is shown below:
(Recall that we configured LoginManager as a managed bean called mgr.)
j. select userID from the code-completion window; complete the expression with
the closing {
k. insert another <h:inputText> element; set its value binding expression to
value="#{mgr.password}"
l. insert a <h:commandButton> element; set its value to Login, and its action
to the value binding expression #{mgr.loginAction}
The final code, with the barest presentational formatting, is shown below:
<%@ page contentType="text/html; charset=Cp1252" %>
<%@ taglib uri="http://java.sun.com/jsf/html" prefix="h" %>
<%@ taglib uri="http://java.sun.com/jsf/core" prefix="f" %>
<html>
155
12 - javaserver faces
<head>
<title>jsf-title</title>
</head>
<body>
<f:view>
<h:form>
UserID: <h:inputText value="#{mgr.userID}"/>
<br/>Password: <h:inputText
value="#{mgr.password}"/>
<br/><h:commandButton value="Login"
action="#{mgr.loginAction}"/>
</h:form>
</f:view>
</body>
</html>
12.8.5 Creating Navigation Rules
Here we create navigation rules among pages, using a FacesIDE editor.
1. Open faces-config.xml; it should open in the faces-config.xml Editor.
2. Select the Navigation tab
3. from the Navigation panel in the palette at left, click on Page, then click inside the editor
window; this inserts a page icon into the editor, and the page's properties appear in the
Workbech's Properties view. This is shown below.
Note that the icon has a small triangle overlay--this indicates that something is wrong,
156
12 - javaserver faces
specifically that FacesIDE could not locate a page at path /page1.jsp
4. in the Properties view, change the value of path to /index.jsp. You can also change
it on the diagram directly (select the page and click once more); notice that the warning
triangle disappears.
5. add 3 more pages, and set them to /pages/login.jsp, /pages/success.jsp and
/pages/error.jsp. Arrange them as shown below:
Now we'll add navigation rules among the pages.
6. from the palette at left, select Navigation Case, then click first on the icon for
login.jsp and then on the icon for success.jsp. This inserts a forward-action
between the two pages, and is represented by an arrow. "Decharge" the mouse pointer by
clicking on the pointer icon in the palette, then click on the newly-added forward-action
icon to select it. Its properties appear in the Properties view. This is shown below:
157
12 - javaserver faces
7. in the Properties view (or direct editing on the diagram), change the value of fromoutcome to loginPass. Recall that this is the success-value returned by
LoginManager's loginAction method. You can also change values by direct-editing
(select once and re-click) in the diagram
8. Similarly add a forward-action from login.jsp to error.jsp, and set its fromoutcome to loginFail
We're done with setting up navigation rules. We'll set some properties in web.xml, and we'll
then be ready to deploy the application.
12.8.6 Editing web.xml
Here we edit web.xml for the specifics of our application. As it turns out, since we have such a
trivial application, all we need do in web.xml is indicate the Faces Servlet mapping.
1. open web.xml; scroll to the bottom and look for the comment
<!-- Faces Servlet Mapping -->
2. by default virtual path-based mapping is commented out, and extension-based mapping is
turned on. We want virtual path-based mapping, so uncomment it. You may comment out
the entry for extension-based mapping, or leave it as-is.
The application is now complete, and you should be able to deploy it to your server of choice.
Once deployed browse to index.jsp, and you should be automatically forwarded to
login.jsp. Use UserID/Password of foo/bar, and you should be sent to the success page; any
other id/password should send you to the error page.
Deployment to some servers is described below:
158
12 - javaserver faces
12.8.7 Deploying To Tomcat 5.0
1. start Tomcat; open its Manager application in a browser; the default URL for this is
http://localhost:8080/manager/html
2. scroll down to Deploy; we'll deploy our app by providing its directory; for Context path
enter /jsf-login; for WAR or Directory URL enter the path to webroot, as
file:///...; leave XML Configuration File URL blank; click Deploy
3. the Manager application should reload, and you should see /jsf-login in the list of
running applications. Click on its link to launch the application.
12.9 packges in the JavaServer Faces API
The classes and interfaces of the JavaServer Faces API are grouped in several packages,
namely:
•
javax.faces
•
javax.faces.application
•
javax.faces.component
•
javax.faces.component.html
•
javax.faces.context
•
javax.faces.convert
•
javax.faces.el
•
javax.faces.event
•
javax.faces.lifecycle
•
javax.faces.model
•
javax.faces.render
•
javax.faces.validator
•
javax.faces.webapp
12.10 the javax.faces package
Contains 2 classes – FactoryFinder and FacesException
public final class FactoryFinder extends Object
FactoryFinder implements the standard discovery algorithm for all factory objects specified in
the JavaServer Faces APIs. For a given factory class name, a corresponding implementation
class is searched for based on the following algorithm. Items are listed in order of decreasing
search precedence:
•
If the JavaServer Faces configuration file bundled into the WEB-INF directory of the
webapp contains a factory entry of the given factory class name, that factory is used.
•
If the JavaServer Faces configuration files named by the javax.faces.CONFIG_FILES
159
12 - javaserver faces
ServletContext init parameter contain any factory entries of the given factory class
name, those factories are used, with the last one taking precedence.
•
If there are any JavaServer Faces configuration files bundled into the META-INF directory
of any jars on the ServletContext's resource paths, the factory entries of the given
factory class name in those files are used, with the last one taking precedence.
•
If a META-INF/services/{factory-class-name} resource is visible to the web
application class loader for the calling application (typically as a result of being present in
the manifest of a JAR file), its first line is read and assumed to be the name of the factory
implementation class to use.
•
If none of the above steps yield a match, the JavaServer Faces implementation specific
class is used.
public class FacesException extends RuntimeException
This class encapsulates general JavaServer Faces exceptions.
12.11 the javax.faces.application package
Contains the following classes:
•
Application - A set of APIs for representing UI components and managing their state,
handling events and input validation, defining page navigation, and supporting
internationalization and accessibility.
•
ApplicationFactory - a factory object that creates (if needed) and returns Application
instances. Implementations of JavaServer Faces must provide at least a default
implementation of Application.
•
FacesMessage - represents a single validation (or other) message, which is typically
associated with a particular component in the view. A FacesMessage instance may be
created based on a specific messageId.
•
FacesMessage.Severity - used to represent message severity levels in a typesafe
enumeration.
•
NavigationHandler – An object of this type is passed the outcome string returned by an
application action invoked for this application, and will use this (along with related state
information) to choose the view to be displayed next.
•
StateManager - directs the process of saving and restoring the view between requests.
•
StateManagerWrapper - Provides a simple implementation of StateManager that can
be subclassed by developers wishing to provide specialized behavior to an existing
StateManager instance. The default implementation of all methods is to call through to
the wrapped StateManager.
•
ViewHandler - the pluggablity mechanism for allowing implementations of or applications
using the JavaServer Faces specification to provide their own handling of the activities in
the Render Response and Restore View phases of the request processing lifecycle. This
allows for implementations to support different response generation technologies, as well
as alternative strategies for saving and restoring the state of each view.
•
ViewHandlerWrapper - Provides a simple implementation of ViewHandler that can be
160
12 - javaserver faces
subclassed by developers wishing to provide specialized behavior to an existing
ViewHandler instance. The default implementation of all methods is to call through to
the wrapped ViewHandler.
•
ViewExpiredException - implementations must throw this FacesException when
attempting to restore the view
StateManager.restoreView(javax.faces.context.FacesContext, String,
String) results in failure on postback.
12.12 the javax.faces.component package
Defines both a set of interfaces and classes. The interfaces defined in this package are:
•
ActionSource - an interface that may be implemented by any concrete UIComponent
that wishes to be a source of ActionEvents, including the ability to invoke application
actions via the default ActionListener mechanism.
•
ActionSource2 - extends ActionSource and provides a JavaBeans property analogous
to the "action" property on ActionSource. The difference is the type of this property is
a MethodExpression rather than a MethodBinding. This allows the ActionSource
concept to leverage the new Unified EL API.
•
ContextCallBack - A simple callback interace that enables taking action on a specific
UIComponent (either facet or child) in the view while preserving any contextual state for
that component instance in the view.
•
EditableValueHolder - an extension of ValueHolder that describes additional features
supported by editable components, including ValueChangeEvents and Validators.
•
NamingContainer - an interface that must be implemented by any UIComponent that
wants to be a naming container.
•
StateHolder - interface implemented by classes that need to save their state between
requests.
•
ValueHolder - an interface that may be implemented by any concrete UIComponent that
wishes to support a local value, as well as access data in the model tier via a value
binding expression, and support conversion between String and the model tier data's
native data type.
The classes in this package are all UI related. Here they are:
•
UIColumn - a UIComponent that represents a single column of data within a parent
UIData component.
•
UICommand - a UIComponent that represents a user interface component which, when
activated by the user, triggers an application specific "command" or "action". Such a
component is typically rendered as a push button, a menu item, or a hyperlink.
•
UIComponent - the base class for all user interface components in JavaServer Faces.
The set of UIComponent instances associated with a particular request and response are
organized into a component tree under a UIViewRoot that represents the entire content
of the request or response.
•
UIComponentBase - a convenience base class that implements the default concrete
behavior of all methods defined by UIComponent.
161
12 - javaserver faces
•
UIData - a UIComponent that supports data binding to a collection of data objects
represented by a DataModel instance, which is the current value of this component itself
(typically established via a ValueBinding). During iterative processing over the rows of
data in the data model, the object for the current row is exposed as a request attribute
under the key specified by the var property.
•
UIForm - a UIComponent that represents an input form to be presented to the user, and
whose child components represent (among other things) the input fields to be included
when the form is submitted.
•
UIGraphic - a UIComponent that displays a graphical image to the user. The user cannot
manipulate this component; it is for display purposes only.
•
UIInput - a UIComponent that represents a component that both displays output to the
user (like UIOutput components do) and processes request parameters on the
subsequent request that need to be decoded.
•
UIMessage - This component is responsible for displaying messages for a specific
UIComponent, identified by a clientId.
•
UIMessages - The renderer for this component is responsible for obtaining the messages
from the FacesContext and displaying them to the user.
•
UINamingContainer - a convenience base class for components that wish to implement
NamingContainer functionality.
•
UIOutput - a UIComponent that has a value, optionally retrieved from a model tier bean
via a value binding expression, that is displayed to the user. The user cannot directly
modify the rendered value; it is for display purposes only.
•
UIPanel - a UIComponent that manages the layout of its child components.
•
UIParameter - a UIComponent that represents an optionally named configuration
parameter for a parent component.
•
UISelectBoolean - a UIComponent that represents a single boolean (true or false)
value. It is most commonly rendered as a checkbox.
•
UISelectItem - a component that may be nested inside a UISelectMany or
UISelectOne component, and causes the addition of a SelectItem instance to the list
of available options for the parent component.
•
UISelectMany - a UIComponent that represents the user's choice of a zero or more
items from among a discrete set of available options. The user can modify the selected
values. Optionally, the component can be preconfigured with zero or more currently
selected items, by storing them as an array in the value property of the component.This
component is generally rendered as a select box or a group of checkboxes.
•
UISelectOne - a UIComponent that represents the user's choice of zero or one items
from among a discrete set of available options. The user can modify the selected value.
Optionally, the component can be preconfigured with a currently selected item, by storing
it as the value property of the component.
•
UIViewRoot - the UIComponent that represents the root of the UIComponent tree. This
component has no rendering, it just serves as the root of the component tree.
12.13 the java.faces.component.html package
162
12 - javaserver faces
Contains HTML related classes.
•
HtmlColumn - represents a column that will be rendered in an HTML table element.
•
HtmlCommandButton - represents an HTML input element for a button of type
submit or reset. The label text is specified by the component value.
•
HtmlCommandLink - represents an HTML a element for a hyperlink that acts like a
submit button. This component must be placed inside a form, and requires JavaScript to
be enabled in the client.
•
HtmlDataTable - represents a set of repeating data (segregated into columns by child
UIColumn components) that will be rendered in an HTML table element.
•
HtmlForm - represents an HTML form element. Child input components will be
submitted unless they have been disabled.
•
HtmlGraphicImage - represents an HTML img element, used to retrieve and render a
graphical image.
•
HtmlInputHidden - represents an HTML input element of type hidden.
•
HtmlInputSecret - represents an HTML input element of type password. On a
redisplay, any previously entered value will not be rendered (for security reasons) unless
the redisplay property is set to true.
•
HtmlInputText - represents an HTML input element of type text.
•
HtmlInputTextarea - represents an HTML textarea element.
•
HtmlMessage - by default, the rendererType property must be set to
"javax.faces.Message". This value can be changed by calling the
setRendererType() method.
•
HtmlMessages - by default, the rendererType property must be set to
"javax.faces.Messages" This value can be changed by calling the
setRendererType() method.
•
HtmlOutputFormat - represents a component that looks up a localized message in a
resource bundle, optionally uses it as a MessageFormat pattern string and substitutes in
parameter values from nested UIParameter components, and renders the result. If the
"dir" or "lang" attributes are present, render a span element and pass them through as
attributes on the span.
•
HtmlOutputLabel - represents an HTML label element, used to define an accessible
label for a corresponding input element.
•
HtmlOutputLink - represents an HTML a (hyperlink) element that may be used to link to
an arbitrary URL defined by the value property.
•
HtmlOutputText - renders the component value as text, optionally wrapping in a span
element if CSS styles or style classes are specified.
•
HtmlPanelGrid - renders child components in a table, starting a new row after the
specified number of columns.
•
HtmlPanelGroup - causes all child components of this component to be rendered. This is
useful in scenarios where a parent component is expecting a single component to be
present, but the application wishes to render more than one.
•
HtmlSelectBooleanCheckbox - represents an HTML input element of type checkbox.
The checkbox will be rendered as checked, or not, based on the value of the value
163
12 - javaserver faces
property.
•
HtmlSelectManyCheckbox - represents a multiple-selection component that is rendered
as a set of HTML input elements of type checkbox.
•
HtmlSelectManyListbox - represents a multiple-selection component that is rendered as
an HTML select element, showing either all available options or the specified number of
options.
•
HtmlSelectManyMenu - represents a multiple-selection component that is rendered as an
HTML select element, showing a single available option at a time.
•
HtmlSelectOneListbox - represents a single-selection component that is rendered as an
HTML select element, showing either all available options or the specified number of
options.
•
HtmlSelectOneMenu - represents a single-selection component that is rendered as an
HTML select element, showing a single available option at a time.
•
HtmlSelectOneRadio - represents a single-selection component that is rendered as a set
of HTML input elements of typeradio.
12.14 the java.faces.context package
Contains the following classes:
•
ExternalContext - allows the Faces API to be unaware of the nature of its containing
application environment. In particular, this class allows JavaServer Faces based
applications to run in either a Servlet or a Portlet environment.
•
FacesContext - contains all of the per-request state information related to the processing
of a single JavaServer Faces request, and the rendering of the corresponding response. It
is passed to, and potentially modified by, each phase of the request processing lifecycle.
•
FacesContextFactory - a factory object that creates (if needed) and returns new
FacesContext instances, initialized for the processing of the specified request and
response objects.
•
ResponseStream - an interface describing an adapter to an underlying output
mechanism for binary output.
•
ResponseWriter - an abstract class describing an adapter to an underlying output
mechanism for character-based output.
•
ResponseWriterWrapper - provides a simple implementation of ResponseWriter that
can be subclassed by developers wishing to provide specialized behavior to an existing
ResponseWriter instance. The default implementation of all methods is to call through
to the wrapped ResponseWriter.
12.15 the java.faces.convert package
164
12 - javaserver faces
12.15.1 the interface Converter
Converter is an interface describing a Java class that can perform Object-to-String and Stringto-Object conversions between model data objects and a String representation of those objects
that is suitable for rendering.
The classes implementing this interface within this package are:
•
BigDecimalConverter
•
BigIntegerConverter
•
BooleanConverter
•
ByteConverter
•
CharacterConverter
•
DateTimeConverter
•
DoubleConverter
•
EnumConverter
•
FLoatConverter
•
IntegerConverter
•
LongConverter
•
NumberConverter
•
ShortConverter
The package also contains one exception:
•
ConverterException - an exception thrown by the getAsObject() or getAsText()
method of a Converter, to indicate that the requested conversion cannot be performed.
12.16 the java.faces.el package
Contains classes and interfaces for evaluating and processing reference expressions.
Classes:
•
MethodBinding - an object that can be used to call an arbitrary public method, on an
instance that is acquired by evaluatng the leading portion of a method binding expression
via a ValueBinding.
•
PropertyResolver - represents a pluggable mechanism for accessing a "property" of an
underlying Java object instance.
•
ValueBinding - an object that can be used to access the property represented by an
action or value binding expression.
•
VariableResolver - represents a pluggable mechanism for resolving a top-level variable
reference at evaluation time.
165
12 - javaserver faces
Exceptions:
•
EvaluationException - an exception reporting an error that occurred during the
evaluation of an expression in a MethodBinding or ValueBinding.
•
MethodNotFoundException - an exception caused by a method name that cannot be
resolved against a base object.
•
PropertyNotFoundException - an exception caused by a property name that cannot be
resolved against a base object.
•
ReferenceSyntaxException - an exception reporting a syntax error in a method binding
expression or value binding expression.
12.17 the java.faces.event package
Contains interfaces describing events and event listeners, and event implementation classes.
Interfaces:
•
ActionListener - listener interface for receiving ActionEvents.
•
FacesListener - a generic base interface for event listeners for various types of
FacesEvents.
•
PhaseListener - interface implemented by objects that wish to be notified at the
beginning and ending of processing for each standard phase of the request processing
lifecycle.
•
ValueChangeListener - listener interface for receiving ValueChangeEvents.
Classes:
•
ActionEvent - represents the activation of a user interface component (such as a
UICommand).
•
FacesEvent - the base class for user interface and application events that can be fired by
UIComponents.
•
PhaseEvent - represents the beginning or ending of processing for a particular phase of
the request processing lifecycle, for the request encapsulated by the specified
FacesContext.
•
PhaseId - typesafe enumeration of the legal values that may be returned by the
getPhaseId() method of the FacesEvent interface.
•
ValueChangeEvent - a notification that the local value of the source component has
been change as a result of user interface activity.
One exception - AbortProcessingException - thrown by event listeners to terminate the
processing of the current event.
166
12 - javaserver faces
12.18 the java.faces.lifecycle package
This package contains 2 classes.
The Lifecycle class manages the processing of the entire lifecycle of a particular JavaServer
Faces request.
The LifecycleFactory class is a factory object that creates (if needed) and returns Lifecycle
instances.
12.19 the java.faces.model package
Contains the interface DataModelListener and several classes providing standard model data
beans for JavaServer Faces. Classes:
•
ArrayDataModel - a convenience implementation of DataModel that wraps an array of
Java objects.
•
DataModel - an abstraction around arbitrary data binding technologies that can be used to
adapt a variety of data sources for use by JavaServer Faces components that support
per-row processing for their child components (such as UIData).
•
DataModelEvent - represents an event of interest to registered listeners that occurred on
the specified DataModel.
•
ListDataModel - a convenience implementation of DataModel that wraps an List of
Java objects.
•
ResultDataModel - a convenience implementation of DataModel that wraps a JSTL
Result object, typically representing the results of executing an SQL query via JSTL
tags.
•
ResultSetDataModel - a convenience implementation of DataModel that wraps a
ResultSet of Java objects. Note that the specified ResultSet MUST be scrollable.
•
ScalarDataModel - a convenience implementation of DataModel that wraps an
individual Java object.
•
SelectItem - represents a single item in the list of supported items associated with a
UISelectMany or UISelectOne component.
•
SelectItemGroup - a subclass of SelectItem that identifies a set of options that will be
made available as a subordinate "submenu" or "options list", depending upon the
requirements of the UISelectMany or UISelectOne renderer that is actually used.
12.20 the java.faces.render package
Contains classes defining the rendering model.
•
Renderer - converts the internal representation of UIComponents into the output stream
167
12 - javaserver faces
(or writer) associated with the response we are creating for a particular request. Each
Renderer knows how to render one or more UIComponent types (or classes), and
advertises a set of render-dependent attributes that it recognizes for each supported
UIComponent.
•
RenderKit - represents a collection of Renderer instances that, together, know how to
render JavaServer Faces UIComponent instances for a specific client. Typically,
RenderKits are specialized for some combination of client device type, markup
language, and/or user Locale. A RenderKit also acts as a Factory for associated
Renderer instances, which perform the actual rendering process for each component.
•
RenderKitFactory - a factory object that registers and returns RenderKit instances.
Implementations of JavaServer Faces must provide at least a default implementation of
RenderKit.
•
ResponseStateManager - the helper class to StateManager that knows the specific
rendering technology being used to generate the response.
12.21 the java.faces.validator package
Interface defining the validator model, and concrete validator implementation classes.
A Validator implementation is a class that can perform validation (correctness checks) on a
EditableValueHolder.
Implementation classes:
•
DoubleRangeVlidator - a Validator that checks the value of the corresponding
component against specified minimum and maximum values
•
LengthValidator - a Validator that checks the number of characters in the String
representation of the value of the associated component.
•
LongRangeValidator - a Validator that checks the value of the corresponding
component against specified minimum and maximum values.
The package contains an exception, as well.
A ValidatorException is an exception thrown by the validate() method of a Validator to
indicate that validation failed.
12.22 the java.faces.webapp package
Contains classes required for integration of JavaServer Faces into web applications, including a
standard servlet, base classes for JSP custom component tags, and concrete tag implementations
for core tags.
•
AttributeTag - Tag implementation that adds an attribute with a specified name and
String value to the component whose tag it is nested inside, if the component does not
already contain an attribute with the same name.
•
ConverterTag - a base class for all JSP custom actions that create and register a
Converter instance on the ValueHolder associated with our most immediate
168
12 - javaserver faces
surrounding instance of a tag whose implementation class is a subclass of
UIComponentTag.
•
FacesServlet - a servlet that manages the request processing lifecycle for web
applications that are utilizing JavaServer Faces to construct the user interface.
•
FacetTag - the JSP mechanism for denoting a UIComponent is to be added as a facet
to the component associated with its parent.
•
UIComponentBodyTag - a base class for all JSP custom actions, related to a
UIComponent, that need to process their tag bodies.
•
UIComponentTag - the base class for all JSP custom actions that correspond to user
interface components in a page that is rendered by JavaServer Faces.
•
ValidatorTag - a base class for all JSP custom actions that create and register a
Validator instance on the EditableValueHolder associated with our most
immediate surrounding instance of a tag whose implementation class is a subclass of
UIComponentTag.
12.23 the JSF lifecycle
Regardless of whether you are using JSF with JSP pages, servlets, or some other web
technology, each request/response flow that involves JSF follows a certain life cycle. Several
kinds of request/response cycles can occur in a JSF-enabled application. You can have a request
that comes from a previously rendered JSF page (a JSF request) and a request that comes from
a non-JSF page (a non-JSF request). Likewise, you can have a JSF response or a non-JSF
response. We are concerned with these three request/response pairs:
•
Non-JSF request generates JSF response
•
JSF request generates JSF response
•
JSF request generates non-JSF response
Of course, you can also have a non-JSF request that generates a non-JSF response. Because
this does not involve JSF in any way, the JSF life cycle does not apply.
JSP pages have a relatively simple life cycle. A JSP page source is compiled into a page
implementation class. When a web server receives a request, that request is passed to the
container, which passes the request to the page class. The page class processes the request and
then writes the response back to the client. When other pages are included or the request is
forwarded, or when an exception occurs, the process includes a few more components or pages,
but basically, a small set of classes processes a request and sends back a response.
When using JSF, the life cycle is more complicated. This is because the core of JSF is the
MVC pattern, which has several implications. User actions in JSF-generated views take place in a
client that does not have a permanent connection to the server. The delivery of user actions or
page events is delayed until a new connection is established. The JSF life cycle must handle this
delay between event and event processing. Also, the JSF life cycle must ensure that the view is
correct before rendering the view. To ensure that the business state is never invalid, the JSF
system includes a phase for validating inputs and another for updating the model only after all
inputs pass validation.
In MVC, the presentation of data (the view) is separate from its representation in the system
(the model). When the model is updated, the controller sends a message to the view, telling the
view to update its presentation. When the user takes some action with the presentation, the
controller sends a message to the model, telling the model to update its data. In JSF, the model is
composed of business objects that are usually implemented as JavaBeans, the controller is the
169
12 - javaserver faces
JSF implementation, and the UI components are the view.
The JSF life cycle has six phases as defined by the JSF specification:
• Restore View: In this phase, the JSF implementation restores the objects and data structures
that represent the view of the request. If this is the client’s first visit to a page, the JSF
implementation must create the view. When a JSF implementation creates and renders a JSFenabled page, it creates UI objects for each view component. The components are stored in a
component tree, and the state of the UI view is saved for subsequent requests. If this is a
subsequent request, the saved UI view is retrieved for the processing of the current request.
• Apply Request Values: Any data that was sent as part of the request is passed to the
appropriate UI objects that compose the view. These objects update their state with the data
values. Data can come from input fields in a web form, from cookies sent as part of the request,
or from request headers. Data for some components, such as components that create HTML input
fields, is validated at this time. Note that this does not yet update the business objects that
compose the model. It updates only the UI components with the new data.
• Process Validations: The data that was submitted with the form is validated (if it was not
validated in the previous phase). As with the previous phase, this does not yet update the
business objects in the application. This is because if the JSF implementation began to update the
business objects as data was validated, and a piece of data failed validation, the model would be
partially updated and in an invalid state.
• Update Model Values: After all validations are complete, the business objects that make up
the application are updated with the validated data from the request. In addition, if any of the data
needs to be converted to a different format to update the model (for example, converting a String
to a Date object), the conversion occurs in this phase. Conversion is needed when the data type
of a property is not a String or a Java primitive.
• Invoke Application: During this phase, the action method of any command button or link that
was activated is called. In addition, any events that were generated during previous phases and
that have not yet been handled are passed to the web application so that it can complete any
other processing of the request that is required.
• Render Response: The response UI components are rendered, and the response is sent to
the client. The state of the UI components is saved so that the component tree can be restored
when the client sends another request. For a JSF-enabled application, the thread of execution for
a request/response cycle can flow through each phase, in the order listed here and as shown in
the figure below. However, depending on the request, and what happens during the processing
and response, not every request will flow through all six phases.
170
12 - javaserver faces
In the above figure, you can see a number of optional paths through the life cycle. For example,
if errors occur during any of the phases, the flow of execution transfers immediately to the Render
Response phase, skipping any remaining phases. One way this might occur is if input data is
incorrect or invalid. If data fails validation in either the Apply Request Values or Process
Validations phase, information about the error is saved and processing proceeds directly to the
Render Response phase. Also, if at any point in the life cycle the request processing is complete
and a non-JSF response is to be sent to the client, the flow of execution can exit the life cycle
without completing further phases.
171
13 - JNDI
13 - JNDI
13.1 what is JNDI?
JNDI is an API specified in Java technology that provides naming and directory functionality to
applications written in the Java programming language. It is designed especially for the Java
platform using Java's object model. Using JNDI, applications based on Java technology can store
and retrieve named Java objects of any type. In addition, JNDI provides methods for performing
standard directory operations, such as associating attributes with objects and searching for objects
using their attributes.
JNDI is also defined independent of any specific naming or directory service implementation. It
enables applications to access different, possibly multiple, naming and directory services using a
common API. Different naming and directory service providers can be plugged in seamlessly
behind this common API. This enables Java technology-based applications to take advantage of
information in a variety of existing naming and directory services, such as LDAP, NDS, DNS, and
NIS(YP), as well as enabling the applications to coexist with legacy software and systems.
13.2 naming concepts
A fundamental facility in any computing system is the naming service--the means by which
names are associated with objects and and objects are found based on their names. When using
almost any computer program or system, you are always naming one object or another. For
example, when you use an electronic mail system, you must provide the name of the recipient to
whom you want to send mail. To access a file in the computer, you must supply its name. A
naming service allows you to look up an object given its name.
A naming service's primary function is to map people-friendly names to objects, such as
addresses, identifiers, or objects typically used by computer programs. For example, the Internet
Domain Name System (DNS) maps machine names (such as www.sun.com) to IP addresses
(such as 192.9.48.5). A file system maps a filename (for example, c:\bin\autoexec.bat)
to a file handle that a program can use to access the contents of the file. These two examples
also illustrate the wide range of scale at which naming services exist--from naming an object on
the Internet to naming a file on the local file system.
13.2.1 names
To look up an object in a naming system, you supply it the name of the object. The naming
system determines the syntax that the name must follow. This syntax is sometimes called the
naming system's naming convention.
For example, the UNIXTM file system's naming convention is that a file is named from its path
relative to the root of the file system, with each component in the path separated from left to right
using the forward slash character ("/"). The UNIX pathname, /usr/hello, for example, names a
file hello in the file directory usr, which is located in the root of the file system.
The DNS naming convention calls for components in the DNS name to be ordered from right to
left and delimited by the dot character ("."). Thus the DNS name sales.Wiz.COM names a DNS
entry with the name sales, relative to the DNS entry Wiz.COM. The DNS entry Wiz.COM, in turn,
names an entry with the name Wiz in the COM entry.
172
13 - JNDI
The Lightweight Directory Access Protocol (LDAP) naming convention orders components from
right to left, delimited by the comma character (","). Thus the LDAP name cn=Rosanna Lee,
o=Sun, c=US names an LDAP entry cn=Rosanna Lee, relative to the entry o=Sun, which in
turn, is relative to c=us. The LDAP has the further rule that each component of the name must be
a name/value pair with the name and value separated by an equals character ("=").
13.2.2 bindings
The association of a name with an object is called a binding. For example, a file name is bound
to a file.
The DNS contains bindings that map machine names to IP addresses. An LDAP name is bound
to an LDAP entry.
13.2.3 references and addresses
Depending on the naming service, some objects cannot be stored directly; that is, a copy of the
object cannot be placed inside the naming service. Instead, they must be stored by reference; that
is, a pointer or reference to the object is placed inside the naming service. A reference is
information about how to access an object. Typically, it is a much more compact representation
that can be used to communicate with the object, while the object itself might contain more state
information. Using the reference, you can contact the object and obtain more information about
the object.
For example, an airplane object might contain a list of the airplane's passengers and crew, its
flight plan, and fuel and instrument status, and its flight number and departure time. By contrast,
an airplane object reference might contain only its flight number and departure time. The
reference is a much more compact representation of information about the airplane object and
can be used to obtain additional information. A file object, for example, is accessed using a file
reference, also called a file handle. A printer object, for example, might contain the state of the
printer, such as its current queue and the amount of paper in the paper tray. A printer object
reference, on the other hand, might contain only information on how to reach the printer, such as
its print server name and printing protocol.
Although in general a reference can contain any arbitrary information, it is useful to refer to its
contents as addresses (or communication end points): specific information about how to access
the object.
For simplicity, this tutorial uses "object" to refer to both objects and object references when a
distinction between the two is not required.
13.2.4 context
A context is a set of name-to-object bindings. Every context has an associated naming
convention. A context provides a lookup (resolution) operation that returns the object and may
provide operations such as those for binding names, unbinding names, and listing bound names.
A name in one context object can be bound to another context object (called a subcontext) that
has the same naming convention.
For example, a file directory, such as /usr, in the UNIX file system is a context. A file directory
named relative to another file directory is a subcontext (some UNIX users refer to this as a
subdirectory). That is, in a file directory /usr/bin, the directory bin is a subcontext of usr. In
another example, a DNS domain, such as COM, is a context. A DNS domain named relative to
another DNS domain is a subcontext. For example, in the DNS domain Sun.COM, the DNS
domain Sun is a subcontext of COM.
Finally, an LDAP entry, such as c=us, is a context. An LDAP entry named relative to another
LDAP entry is a subcontext. For example, in the an LDAP entry o=sun,c=us, the entry o=sun is
a subcontext of c=us.
173
13 - JNDI
If we imagine all the resources available for us as a collection of rooted trees, one context can
be viewed, in a first and raw approximation as a node in one of these trees. And it kind of makes
sense, because we can, to some extent, identify a web application with its root directory (a node in
the file system directory tree).
13.2.5 naming systems and namespaces
A naming system is a connected set of contexts of the same type (they have the same naming
convention) and provides a common set of operations.
For example, a system that implements the DNS is a naming system. A system that
communicates using the LDAP is a naming system.
A naming system provides a naming service to its customers for performing naming-related
operations. A naming service is accessed through its own interface. For example, the DNS offers
a naming service that maps machine names to IP addresses. The LDAP offers a naming service
that maps LDAP names to LDAP entries. A file system offers a naming service that maps
filenames to files and directories.
A namespace is the set of names in a naming system. For example, the UNIX file system has a
namespace consisting of all of the names of files and directories in that file system. The DNS
namespace contains names of DNS domains and entries. The LDAP namespace contains names
of LDAP entries.
13.3 directory services
Many naming services are extended with a directory service. A directory service associates
names with objects and also allows such objects to have attributes. Thus, you not only can look
up an object by its name but also get the object's attributes or search for the object based on its
attributes.
An example is the telephone company's directory service. It maps a subscriber's name to his
address and phone number. A computer's directory service is very much like a telephone
company's directory service in that both can be used to store information such as telephone
numbers and addresses. The computer's directory service is much more powerful, however,
because it is available online and can be used to store a variety of information that can be utilized
by users, programs, and even the computer itself and other computers.
A directory object represents an object in a computing environment. A directory object can be
used, for example, to represent a printer, a person, a computer, or a network. A directory object
contains attributes that describe the object that it represents.
13.3.1 attributes
A directory object can have attributes. For example, a printer might be represented by a
directory object that has as attributes its speed, resolution, and color. A user might be represented
by a directory object that has as attributes the user's e-mail address, various telephone numbers,
postal mail address, and computer account information.
An attribute has an attribute identifier and a set of attribute values. An attribute identifier is a
token that identifies an attribute independent of its values. For example, two different computer
accounts might have a "mail" attribute; "mail" is the attribute identifier. An attribute value is
the contents of the attribute. The email address, for example, might have an attribute identifier of
"mail" and the attribute value of "[email protected]".
174
13 - JNDI
13.3.2 directories and directory services
A directory is a connected set of directory objects. A directory service is a service that provides
operations for creating, adding, removing, and modifying the attributes associated with objects in
a directory. The service is accessed through its own interface.
Many examples of directory services are possible. The Novell Directory Service (NDS) is a
directory service from Novell that provides information about many networking services, such as
the file and print services. Network Information Service (NIS) is a directory service available on
the Solaris operating system for storing system-related information, such as that relating to
machines, networks, printers, and users. The SunONE Directory Server is a general-purpose
directory service based on the Internet standard LDAP.
13.3.3 searches and search filters
You can look up a directory object by supplying its name to the directory service. Alternatively,
many directories, such as those based on the LDAP, support the notion of searches. When you
search, you can supply not a name but a query consisting of a logical expression in which you
specify the attributes that the object or objects must have. The query is called a search filter. This
style of searching is sometimes called reverse lookup or content-based searching. The directory
service searches for and returns the objects that satisfy the search filter.
For example, you can query the directory service to find all users that have the attribute "age"
greater than 40 years. Similarly, you can query it to find all machines whose IP address starts with
"192.113.50".
13.3.4 combining naming and directory services
Directories often arrange their objects in a hierarchy. For example, the LDAP arranges all
directory objects in a tree, called a directory information tree (DIT). Within the DIT, an
organization object, for example, might contain group objects that might in turn contain person
objects. When directory objects are arranged in this way, they play the role of naming contexts in
addition to that of containers of attributes.
13.4 directory-enabled java applications
Directory service is a vital component of network computing. By using a directory service, you
can simplify applications and their administration by centralizing the storage of shared
information. As the use of the Java programming language to write practical applications in a
network environment increases, the ability to access directory services will become essential.
13.4.1 traditional use of the directory
A directory-enabled application is an application that uses a naming or directory service.
Directory-enabled Java applications and applets, like any other program running on the network,
can use the directory in the traditional way, that is, to store and retrieve attributes of directory
objects. A Java mail client program, for example, can use the directory as an address book for
retrieving the addresses of mail recipients. A Java mail transfer agent program can use it to
retrieve mail routing information. And a Java calendar program can use it to retrieve user
preference settings.
Applications can share the common infrastructure provided by the directory. This sharing
makes applications that are deployed across the system, and even the network, more coherent
and manageable. For example, printer configuration and mail routing information can be stored in
the directory so that it can be replicated and distributed for use by all printer-related and mail-
175
13 - JNDI
related applications and services.
13.4.2 the directory as an object store
In addition to using the directory in the traditional way, Java applications can also use it as a
repository for Java objects, that is to store and retrieve Java objects. For example, a Java print
client program should be able to look up a printer object from the directory and send a data
stream to the printer object for printing.
13.5 the JNDI API
The Java Naming and Directory Interface TM (JNDI) is an application programming interface
(API) that provides naming and directory functionality to applications written using the Java TM
programming language. It is defined to be independent of any specific directory service
implementation. Thus a variety of directories--new, emerging, and already deployed--can be
accessed in a common way.
13.5.1 architecture
The JNDI architecture consists of an API and a service provider interface (SPI). Java
applications use the JNDI API to access a variety of naming and directory services. The SPI
enables a variety of naming and directory services to be plugged in transparently, thereby
allowing the Java application using the JNDI API to access their services.
13.5.2 packaging
The JNDI is included in the Java 2 SDK, v1.3 and later releases. It is also available as a Java
Standard Extension for use with the JDK 1.1 and the Java 2 SDK, v1.2. It extends the v1.1 and
v1.2 platforms to provide naming and directory functionality.
To use the JNDI, you must have the JNDI classes and one or more service providers. The Java
2 SDK, v1.3 includes three service providers for the following naming/directory services:
•
Lightweight Directory Access Protocol (LDAP)
•
Common Object Request Broker Architecture (CORBA) Common Object Services (COS)
name service
•
Java Remote Method Invocation (RMI) Registry
Other service providers can be downloaded from the JNDI Web site or obtained from other
vendors. When using the JNDI as a Standard Extension on the JDK 1.1 and Java 2 SDK, v1.2,
you must first download the JNDI classes and one or more service providers.
The JNDI is divided into five packages:
•
javax.naming
•
javax.naming.directory
•
javax.naming.event
•
javax.naming.ldap
•
javax.naming.spi
176
13 - JNDI
13.6 the naming package
The javax.naming package contains classes and interfaces for accessing naming services.
13.6.1 context
The javax.naming package defines a Context
interface, which is the core interface for
looking up, binding/unbinding, renaming objects and creating and destroying subcontexts.
The most commonly used operation is lookup()
. You supply lookup() the name of the
object you want to look up, and it returns the object bound to that name. For example, the
following code fragment looks up a printer and sends a document to the printer object to be
printed.
Printer printer = (Printer)ctx.lookup("treekiller");
printer.print(report);
13.6.2 names
Every naming method in the Context interface has two overloads: one that accepts a Name
argument and one that accepts a java.lang.String name. Name is an interface that
represents a generic name--an ordered sequence of zero or more components. For the methods
in the Context interface, a Name argument that is an instance of CompositeName represents a
composite name , so you can name an object using a name that spans multiple namespaces. A
Name argument of any other type represents a compound name. (Names are covered in the
Beyond the Basics trail.) The overloads that accept Name are useful for applications that need to
manipulate names, that is, composing them, comparing components, and so on.
A java.lang.String name argument represents a composite name. The overloads that
accept java.lang.String names are likely to be more useful for simple applications, such as
those that simply read in a name and look up the corresponding object.
13.6.3 bindings
listBindings() returns an enumeration of name-to-object bindings. Each binding is
represented by an instance of the Binding class. A binding is a tuple containing the name of the
bound object, the name of the object's class, and the object itself.
list() is similar to listBindings(), except that it returns an enumeration of
NameClassPair. NameClassPair contains an object's name and the name of the object's
class. list() is useful for applications such as browsers that want to discover information about
the objects bound within a context but that don't need all of the actual objects. Although
listBindings() provides all of the same information, it is potentially a much more expensive
operation.
13.6.4 references
Objects are stored in naming and directory services in different ways. A service that supports
storing Java objects might support storing an object in its serialized form. However, some naming
and directory services do not support the storing of Java objects. Furthermore, for some objects in
the directory, Java programs are but one group of applications that access them. In this case, a
serialized Java object might not be the most appropriate representation. A reference might be a
very compact representation of an object, whereas its serialized form might contain a lot more
state (see the Naming Concepts lesson).
177
13 - JNDI
The JNDI defines the Reference class to represent a reference. A reference contains
information on how to construct a copy of the object. The JNDI will attempt to turn references
looked up from the directory into the Java objects that they represent so that JNDI clients have
the illusion that what is stored in the directory are Java objects.
13.6.5 the Initial context
In the JNDI, all naming and directory operations are performed relative to a context. There are
no absolute roots. Therefore the JNDI defines an initial context, InitialContext, which
provides a starting point for naming and directory operations. Once you have an initial context,
you can use it to look up other contexts and objects.
13.6.6 exceptions
The JNDI defines a class hierarchy for exceptions that can be thrown in the course of
performing naming and directory operations. The root of this class hierarchy is
NamingException. Programs interested in dealing with a particular exception can catch the
corresponding subclass of the exception. Otherwise, they should catch NamingException.
13.7 directory package
The javax.naming.directory package extends the javax.naming package to provide
functionality for accessing directory services in addition to naming services. This package allows
applications to retrieve attributes associated with objects stored in the directory and to search for
objects using specified attributes.
13.7.1 the directory context
The DirContext interface represents a directory context. It defines methods for examining
and updating attributes associated with a directory object.
You use getAttributes() to retrieve the attributes associated with a directory object (for
which you supply the name). Attributes are modified using modifyAttributes(). You can add,
replace, or remove attributes and/or attribute values using this operation.
DirContext also behaves as a naming context by extending the Context interface. This
means that any directory object can also provide a naming context. For example, a directory
object for a person might contain attributes about that person as well as provide a context for
naming objects, such as the person's printers and file system relative to that person directory
object.
13.7.2 searches
DirContext contains methods for performing content-based searching of the directory. In the
simplest and most common form of usage, the application specifies a set of attributes--possibly
with specific values--to match and submits this attribute set to the search() method. Other
overloaded forms of search() support more sophisticated search filters.
13.8 event package
The javax.naming.event package contains classes and interfaces for supporting event
178
13 - JNDI
notification in naming and directory services. Event notification is described in detail in the
Beyond the Basics trail.
Events
A NamingEvent represents an event that is generated by a naming/directory service. The
event contains a type that identifies the type of event. For example, event types are categorized
into those that affect the namespace, such as "object added," and those that do not, such as
"object changed." A NamingEvent also contains other information about the change, such as
information about the object before and after the change.
Listeners
A NamingListener is an object that listens for NamingEvents. Each category of event type
has a corresponding type of NamingListener. For example, a NamespaceChangeListener
represents a listener interested in namespace change events and an ObjectChangeListener
represents a listener interested in object change events.
To receive event notifications, a listener must be registered with either an EventContext or
an EventDirContext. Once registered, the listener will receive event notifications when the
corresponding changes occur in the naming/directory service.
13.9 LDAP package
The javax.naming.ldap package contains classes and interfaces for using features that are
specific to the LDAP v3 that are not already covered by the more generic
javax.naming.directory package. In fact, most JNDI applications that use the LDAP will find
the javax.naming.directory package sufficient and will not need to use the
javax.naming.ldap package at all. This package is primarily for those applications that need
to use "extended" operations, controls, or unsolicited notifications.
13.9.1 "extended" operation
In addition to specifying well-defined operations such as search and modify, the LDAP v3 (RFC
2251) specifies a way to transmit yet-to-be defined operations between the LDAP client and the
server. These operations are called "extended" operations. An "extended" operation may be
defined by a standards organization such as the Internet Engineering Task Force (IETF) or by a
vendor. This package defines classes for the Start TLS extension.
13.9.2 controls
The LDAP v3 allows any request or response to be augmented by yet-to-be defined modifiers,
called controls . A control sent with a request is a request control and a control sent with a
response is a response control . A control may be defined by a standards organization such as the
IETF or by a vendor. Request controls and response controls are not necessarily paired, that is,
there need not be a response control for each request control sent, and vice versa.
13.9.3 unsolicited notifications
In addition to the normal request/response style of interaction between the client and server, the
LDAP v3 also specifies unsolicited notifications--messages that are sent from the server to the
client asynchronously and not in response to any client request.
179
13 - JNDI
13.9.4 the LDAP context
The LdapContext interface represents a context for performing "extended" operations,
sending request controls, and receiving response controls. Examples of how to use these features
are described in the Controls and Extensions lesson.
13.10 service provider package
The javax.naming.spi package provides the means by which developers of different
naming/directory service providers can develop and hook up their implementations so that the
corresponding services are accessible from applications that use the JNDI.
13.10.1 plug-In architecture
The javax.naming.spi package allows different implementations to be plugged in
dynamically. These implementations include those for the initial context and for contexts that can
be reached from the initial context.
13.10.2 java object support
The javax.naming.spi package supports implementors of Context.lookup() and
related methods to return Java objects that are natural and intuitive for the Java programmer. For
example, if you look up a printer name from the directory, then you likely would expect to get back
a printer object on which to operate. This support is provided in the form of object factories.
This package also provides support for doing the reverse. That is, implementors of
Context.bind() and related methods can accept Java objects and store the objects in a
format acceptable to the underlying naming/directory service. This support is provided in the form
of state factories.
13.10.3 multiple naming systems (federation)
JNDI operations allow applications to supply names that span multiple naming systems. In the
process of completing an operation, one service provider might need to interact with another
service provider, for example to pass on the operation to be continued in the next naming system.
This package provides support for different providers to cooperate to complete JNDI operations.
13.11 naming example
This example shows you how to write a program that looks up an object whose name is passed
in as a command-line argument. It uses a service provider for the file system. Therefore the name
that you supply to the program must be a filename. You do not need to understand details about
the service provider at this point.
13.11.1 importing the JNDI classes
Using your favorite text editor, create a file named Lookup.java. You can import either the
entire package or only individual classes and interfaces. The following code imports each class
that is used from the javax.naming package.
import javax.naming.Context;
import javax.naming.InitialContext;
import javax.naming.NamingException;
180
13 - JNDI
13.11.2 creating an initial context
In the main() method of the program, create an initial context. Indicate that you're using the
file system service provider by setting the environment properties parameter (represented by a
Hashtable class) to the InitialContext constructor, as follows.
Hashtable env = new Hashtable();
env.put(Context.INITIAL_CONTEXT_FACTORY,
"com.sun.jndi.fscontext.RefFSContextFactory");
Context ctx = new InitialContext(env);
How to set up the parameters for this constructor is explained in more detail in The Basics trail.
13.11.3 looking up an Object
Next, use Context.lookup() to look up an object. The following code looks up the object
bound to the name supplied in the command line.
Object obj = ctx.lookup(name);
13.11.4 catching NamingException
The creation of the initial context and the lookup() method can throw a NamingException.
For this reason, you need to enclose these calls inside a try/catch clause. Here's the code
fragment repeated with the try/catch clause.
try {
// Create the initial context
Context ctx = new InitialContext(env);
// Look up an object
Object obj = ctx.lookup(name);
// Print it
System.out.println(name + " is bound to: " + obj);
}
} catch (NamingException e) {
System.err.println("Problem looking up " + name + ":" + e);
13.11.5 compiling the program
Next, you compile the source file using the Java compiler. To compile to program, you must
have access to the JNDI classes. If you are using the Java 2 SDK, v1.3, then the JNDI classes
are already included. Otherwise, you can include the classes either by setting the CLASSPATH
variable to include the jndi.jar that you downloaded from the JNDI Web site or by installing
jndi.jar as an installed extension. See the Preparations lesson for details on how to install the
JNDI classes and service providers.
If the compilation succeeds, then the compiler will create a file named Lookup.class in the
same directory (folder) as the Java source file (Lookup.java). If the compilation fails, then make
sure that you typed in and named the program exactly as shown here, using the capitalization
shown. If you are still having problems, then see the Common Problems lesson for help.
13.11.6 running the program
To run the program, you need access to the JNDI classes, the file system service provider, and
181
13 - JNDI
your example class (Lookup.class). See the compilation step for instructions on including
access to the JNDI classes. To include the file system service provider classes (fscontext.jar
and providerutil.jar), either include them in your CLASSPATH variable or install them as
extensions. Note that these archive files are not included with the Java 2 SDK, v1.3. See the
Preparations lesson for details on how to install the JNDI classes and service providers. Finally,
include the directory that contains your Lookup.class file in your the CLASSPATH variable.
To run the program, supply the name of a file in your file system, as follows:
# java Lookup /tmp
Or as follows:
# java Lookup \autoexec.bat
If you supply a file directory, then you will see something like the following.
# java Lookup /tmp
/tmp is bound to: com.sun.jndi.fscontext.RefFSContext@1dae083f
If the name that you supplied is a file, then you will see something like this:
/tmp/f is bound to: //tmp/f
13.12 directory example
This example shows you how to write a program that retrieves attributes from a directory object.
It uses an LDAP service provider to access an LDAP service.
13.12.1 importing the JNDI directory classes
Using your favorite text editor, create a file named Getattr.java. You can import either the
entire package or only individual classes and interfaces. The following code imports each class
that is used from the javax.naming and javax.naming.directory packages.
import
import
import
import
import
javax.naming.Context;
javax.naming.directory.InitialDirContext;
javax.naming.directory.DirContext;
javax.naming.directory.Attributes;
javax.naming.NamingException;
13.12.2 creating an initial directory context
In the main() method of the program, create an initial directory context. This is similar to
creating an initial context in the previous naming example, except that you use the constructor for
InitialDirContext.
Hashtable env = new Hashtable();
env.put(Context.INITIAL_CONTEXT_FACTORY,
"com.sun.jndi.ldap.LdapCtxFactory");
env.put(Context.PROVIDER_URL,
"ldap://localhost:389/o=JNDITutorial");
DirContext ctx = new InitialDirContext(env);
182
13 - JNDI
Similar to the naming example, you indicate that you're using the LDAP service provider by
setting the Hashtable parameter to the InitialDirContext constructor appropriately. Details
on how to set up the parameters for this constructor are given in The Basics trail. For now, the
only thing to understand is that the program by default identifies an LDAP server on the local
machine. If your LDAP server is located on another machine or is using another port, then you
need to edit the LDAP URL ("ldap://localhost:389/o=JNDITutorial") accordingly.
Instructions for setting up a sample LDAP server for this tutorial are given in the Preparations
lesson.
13.12.3 getting a directory Object's attributes
Next, use getAttributes() to get an object's attributes. The following code retrieves all of
the attributes associated with the object bound to the name "cn=Ted Geisel, ou=People":
Attributes attrs = ctx.getAttributes("cn=Ted Geisel, ou=People");
13.12.4 extracting the desired attribute
From a set of attributes, Attributes, you can ask for a particular attribute by using
Attributes.get() and then from that attribute get its value. The following line first gets the
surname attribute "sn" and then invokes Attribute.get() on it to get its value:
attrs.get("sn").get();
13.12.5 catching NamingException
The method calls shown so far can throw a NamingException. For this reason, you need to
wrap these calls inside a try/catch clause. Here's the code fragment repeated with the
try/catch clause.
try {
// Create the initial directory context
DirContext ctx = new InitialDirContext(env);
// Ask for all attributes of the object
Attributes attrs = ctx.getAttributes("cn=Ted Geisel,
ou=People");
// Find the surname attribute ("sn") and print it
System.out.println("sn: " + attrs.get("sn").get());
}
} catch (NamingException e) {
System.err.println("Problem getting attribute:" + e);
13.12.6 compiling the program
Next, compile the source file using the Java compiler. As with the naming example, to do this
you need access to the JNDI classes.
If the compilation succeeds, then the compiler creates a file named Getattr.class in the
same directory (folder) as the Java source file (Getattr.java). If the compilation fails, then
make sure that you typed in and named the program exactly as shown here, using the
capitalization shown. If you are still having problems, then see the Common Problems lesson for
help.
183
13 - JNDI
13.12.7 running the program
As with the naming example, you need access to both the JNDI classes and your example
class, Getattr.class. You also need access to the LDAP service provider classes (ldap.jar
and providerutil.jar). If you are using the Java 2 SDK, v1.3, then these classes are already
included.
Here's an example of a command line for running Getattr and the output it generates.
# java Getattr
sn: Geisel
Recall that the program was configured with the following property.
env.put(Context.PROVIDER_URL,
"ldap://localhost:389/o=JNDITutorial");
With this configuration, this command queries the LDAP server on machine localhost that is
listening on port 389, serving the "o=JNDITutorial" namespace. (See the Preparations lesson
for details on this configuration step.) It asks for the attributes of the entry "cn=Ted Geisel,
ou=People". Once it has the attributes, it extracts the surname attribute ("sn"). If you have any
trouble running this example, then see the Common Problems lesson.
184
14 - JAVA MESSAGE SERVICE
14 - JAVA MESSAGE SERVICE
14.1 JMS elements
The Java Message Service (JMS) API is a Java Message Oriented Middleware (MOM) API for
sending messages between two or more clients. JMS is a part of the Java Platform, Enterprise
Edition, and is defined by a specification developed under the Java Community Process as JSR
914.
The following are JMS elements:
•
JMS provider - An implementation of the JMS interface for a Message Oriented
Middleware (MOM). Providers are implemented as either a Java JMS implementation or
an adapter to a non-Java MOM.
JMS client - an application or process that produces and/or consumes messages.
•
JMS producer - a JMS client that creates and sends messages.
•
JMS consumer - a JMS client that receives messages.
•
JMS message - an object that contains the data being transferred between JMS clients.
•
JMS queue - a staging area that contains messages that have been sent and are waiting
to be read. As the name queue suggests, the messages are delivered in the order sent. A
message is removed from the queue once it has been read.
•
JMS topic - a distribution mechanism for publishing messages that are delivered to
multiple subscribers.
•
14.2 JMS models
The JMS API supports two models:
•
•
point-to-point or queuing model
publish and subscribe model
In the point-to-point or queuing model, a producer posts messages to a particular queue and
a consumer reads messages from the queue. Here, the producer knows the destination of the
message and posts the message directly to the consumer's queue. It is characterized by following:
•
•
•
Only one consumer will get the message
The producer does not have to be running at the time the consumer consumes the
message, nor does the consumer need to be running at the time the message is sent
Every message successfully processed is acknowledged by the consumer
The publish/subscribe model supports publishing messages to a particular message topic.
Zero or more subscribers may register interest in receiving messages on a particular message
topic. In this model, neither the publisher nor the subscriber know about each other. A good
metaphor for it is anonymous bulletin board. The following are characteristics of this model:
•
•
Multiple consumers can get the message
There is a timing dependency between publishers and subscribers. The publisher has to
create a subscription in order for clients to be able to subscribe. The subscriber has to
remain continuously active to receive messages, unless it has established a durable
185
14 - JAVA MESSAGE SERVICE
subscription. In that case, messages published while the subscriber is not connected will
be redistributed whenever it reconnects.
Using Java, JMS provides a way of separating the application from the transport layer of
providing data. The same Java classes can be used to communicate with different JMS providers
by using the JNDI information for the desired provider. The classes first use a connection factory
to connect to the queue or topic, and then use populate and send or publish the messages. On the
receiving side, the clients then receive or subscribe to the messages.
14.3 the JMS API programming model
14.4 the JMS API
The JMS API is provided in the Java package javax.jms.
14.4.1 the ConnectionFactory interface
An administered object that a client uses to create a connection to the JMS provider. JMS
clients access the connection factory through portable interfaces so the code does not need to be
changed if the underlying implementation changes. Administrators configure the connection
factory in the Java Naming and Directory Interface (JNDI) namespace so that JMS clients can
look them up. Depending on the type of message, users will use either a queue connection factory
or topic connection factory.
186
14 - JAVA MESSAGE SERVICE
At the beginning of a JMS client program, you usually perform a JNDI lookup of a connection
factory, then cast and assign it to a ConnectionFactory object.
For example, the following code fragment obtains an InitialContext object and uses it to
look up a ConnectionFactory by name. Then it assigns it to a ConnectionFactory object:
Context ctx = new InitialContext();
ConnectionFactory connectionFactory = (ConnectionFactory)
ctx.lookup("jms/ConnectionFactory");
In a J2EE application, JMS administered objects are normally placed in the jms naming
subcontext.
14.4.2 the Connection interface
Once a connection factory is obtained, a connection to a JMS provider can be created. A
connection represents a communication link between the application and the messaging server.
Depending on the connection type, connections allow users to create sessions for sending and
receiving messages from a queue or topic.
Connections implement the Connection interface. When you have a ConnectionFactory
object, you can use it to create a Connection:
Connection connection = connectionFactory.createConnection();
Before an application completes, you must close any connections that you have created.
Failure to close a connection can cause resources not to be released by the JMS provider.
Closing a connection also closes its sessions and their message producers and message
consumers.
connection.close();
Before your application can consume messages, you must call the connection's start()
method. If you want to stop message delivery temporarily without closing the connection, you call
the stop() method.
14.4.3 the Destination interface
An administered object that encapsulates the identity of a message destination, which is where
messages are delivered and consumed. It is either a queue or a topic. The JMS administrator
creates these objects, and users discover them using JNDI. Like the connection factory, the
administrator can create two types of destinations: queues for Point-to-Point and topics for
Publish/Subscribe.
For example, the following line of code performs a JNDI lookup of the previously created topic
jms/MyTopic and casts and assigns it to a Destination object:
Destination myDest = (Destination) ctx.lookup("jms/MyTopic");
The following line of code looks up a queue named jms/MyQueue and casts and assigns it to a
Queue object:
Queue myQueue = (Queue) ctx.lookup("jms/MyQueue");
14.4.4 the MessageConsumer interface
An object created by a session. It receives messages sent to a destination. The consumer can
receive messages synchronously (blocking) or asynchronously (non-blocking) for both queue and
187
14 - JAVA MESSAGE SERVICE
topic-type messaging.
For example, you use a Session to create a MessageConsumer for either a queue or a topic:
MessageConsumer consumer = session.createConsumer(myQueue);
MessageConsumer consumer = session.createConsumer(myTopic);
You use the Session.createDurableSubscriber() method to create a durable topic
subscriber. This method is valid only if you are using a topic.
After you have created a message consumer, it becomes active, and you can use it to receive
messages. You can use the close() method for a MessageConsumer to make the message
consumer inactive. Message delivery does not begin until you start the connection you created by
calling its start() method. (Remember always to call the start() method; forgetting to start
the connection is one of the most common JMS programming errors.)
You use the receive method to consume a message synchronously. You can use this method
at any time after you call the start method:
connection.start();
Message m = consumer.receive();
connection.start();
Message m = consumer.receive(1000); // time out after a second
To consume a message asynchronously, a message listener object may be used.
14.4.5 the MessageListener interface
A message listener is an object that acts as an asynchronous event handler for messages.
This object implements the MessageListener interface, which contains one method,
onMessage(). In the onMessage() method, you define the actions to be taken when a message
arrives.
You register the message listener with a specific MessageConsumer by using the
setMessageListener() method. For example, if you define a class named Listener that
implements the MessageListener interface, you can register the message listener as follows:
Listener myListener = new Listener();
consumer.setMessageListener(myListener);
After you register the message listener, you call the start() method on the Connection to
begin message delivery. (If you call start() before you register the message listener, you are
likely to miss messages.)
When message delivery begins, the JMS provider automatically calls the message listener's
onMessage() method whenever a message is delivered. The onMessage() method takes one
argument of type Message, which your implementation of the method can cast to any of the other
message types.
A message listener is not specific to a particular destination type. The same listener can obtain
messages from either a queue or a topic, depending on the type of destination for which the
message consumer was created. A message listener does, however, usually expect a specific
message type and format. Moreover, if it needs to reply to messages, a message listener must
either assume a particular destination type or obtain the destination type of the message and
create a producer for that destination type.
188
14 - JAVA MESSAGE SERVICE
14.4.6 the MessageProducer interface
An object created by a session that sends messages to a destination. The user can create a
sender to a specific destination or create a generic sender that specifies the destination at the
time the message is sent.
You use a Session to create a MessageProducer for a destination. Here, the first example
creates a producer for the destination myQueue, and the second for the destination myTopic:
MessageProducer producer = session.createProducer(myQueue);
MessageProducer producer = session.createProducer(myTopic);
You can create an unidentified producer by specifying null as the argument to
createProducer. With an unidentified producer, you do not specify a destination until you send
a message.
After you have created a message producer, you can use it to send messages by using the
send method:
producer.send(message);
You must first create the messages; if you created an unidentified producer, use an overloaded
send method that specifies the destination as the first parameter. For example:
MessageProducer anon_prod = session.createProducer(null);
anon_prod.send(myQueue, message);
14.4.7 the Message interface
An object that is sent between consumers and producers; that is, from one application to
another. A message has three main parts:
1. A message header (required): Contains operational settings to identify and route
messages
2. A set of message properties (optional): Contains additional properties to support
compatibility with other providers or users. It can be used to create custom fields or filters
(selectors).
3. A message body (optional): Allows users to create five types of messages (text message,
map message, bytes message, stream message, and object message).
The message interface is extremely flexible and provides numerous ways to customize the
contents of a message.
The JMS API provides methods for creating messages of each type and for filling in their
contents. For example, to create and send a TextMessage, you might use the following
statements:
TextMessage message = session.createTextMessage();
message.setText(msg_text);
// msg_text is a String
producer.send(message);
At the consuming end, a message arrives as a generic Message object and must be cast to the
appropriate message type. You can use one or more getter methods to extract the message
contents. The following code fragment uses the getText method:
Message m = consumer.receive();
if (m instanceof TextMessage) {
TextMessage message = (TextMessage) m;
189
14 - JAVA MESSAGE SERVICE
System.out.println("Reading message: " + message.getText());
} else {
// Handle error
}
14.4.8 the Session interface
Represents a single-threaded context for sending and receiving messages. A session is singlethreaded so that messages are serialized, meaning that messages are received one-by-one in the
order sent. The benefit of a session is that it supports transactions. If the user selects transaction
support, the session context holds a group of messages until the transaction is committed, then
delivers the messages. Before committing the transaction, the user can cancel the messages
using a rollback operation. A session allows users to create message producers to send
messages, and message consumers to receive messages.
Sessions implement the Session interface. After you create a Connection object, you use it
to create a Session:
Session session = connection.createSession(false,
Session.AUTO_ACKNOWLEDGE);
The first argument means that the session is not transacted; the second means that the session
automatically acknowledges messages when they have been received successfully.
To create a transacted session, use the following code:
Session session = connection.createSession(true, 0);
Here, the first argument means that the session is transacted; the second indicates that
message acknowledgment is not specified for transacted sessions.
190
15 - ENTERPRISE JAVA BEANS
15 - ENTERPRISE JAVA BEANS
15.1 enterprise java beans versus (ordinary) java beans
(Ordinary) Java beans provide a format for general-purpose components, while the EJB
(Enterprise Java Beans) architecture provides a format for highly specialized business logic
components.
What are Enterprise Java Beans? A collection of Java classes together with an xml file,
bundled into a single unit. The Java classes must follow certain rules and must offer certain
callback methods.
The EJBs will run in an EJB container which is part of an application server.
Version 1.1 of EJB specification provides two EJB types:
•
session beans - intended to be used by a single client (client extension on the server);
bean's life span can be no longer than client's
•
entity beans - object oriented representation of data in a DB; multiple clients can access it
simultaneously while its life-span is the same as the data it represents. Entity beans have
been superseded by the Java Persistence API in EJB 3.0.
The 2.0 EJB specification adds another bean type:
•
message-driven beans
The current EJB specification is 3.0. Novelties in this specification try to make the development
of EJBs easier. It provides annotations for every type of metadata previously addressed by
deployment descriptors, so no XML descriptor is needed and beans deployment can be done just
through a plain .jar file into the application server.
15.2 the ejb container and its services
The EJB container provides an execution environment for a component. The component lives
inside a container, container which offers services to the component. On the other side, the
container lives (in general) in an application server, server which provides an execution
environment for containers.
The main reason for using EJBs is to take advantage of the services provided by the container.
These services are:
•
persistence - DB interaction
•
transactions - transaction management can be complex, especially if we have more
databases and more access components
•
data caching - no developer coding, improved performance
•
security - EJB access can be stated without extra coding
•
error handling - consistent error handling framework - logging, component recovery
•
scalability
•
portability
191
15 - ENTERPRISE JAVA BEANS
•
manageability
15.3 enterprise java beans architecture
An EJB consists of (at least) 3 classes and an xml file. It is bean's programmer task to create
them (at least), as follows:
1. the bean itself (the class that contains the business logic)
2. the home interface of the bean
3. the remote interface of the bean
4. the deployment descriptor, which is an xml file, called ejb-jar.xml
15.4 the home interface
The home interface of an ejb is an interface that extends the EJBHome interface. It provides
methods named create() with application specific arguments, returning the remote interface
and throwing CreateException and RemoteException. It uses only argument types allowed
by the RMI standard.
Handle – abstraction for a network reference to an EJB.
The methods specified by the EJBHome interface (not implemented (in general) by the
programmer) are the following:
public void remove(Handle han) throws RemoteException, RemoveException
public void remove(Object primaryKey) throws RemoteException,
RemoveException
public EJBMetaData getEJBMetaData() throws RemoteException
public HomeHandle getHomeHandle() throws RemoteException
192
15 - ENTERPRISE JAVA BEANS
Code example for the a home interface, called MyBeanHome:
package myBeans;
import.javax.ejb.*;
import java.rmi.RemoteException;
public interface MyBeanHome extends EJBHome
{
MyBeanObject create() throws CreateException,
RemoteException;
}
15.5 the remote interface
The remote interface of a bean is a standard Java interface that extends the EJBObject and
Remote interfaces and declares the business logic methods of the bean. The developer does not
implement this interface.
While the Remote interface declares no methods, the EJBObject declares the following ones:
public EJBHome getEJBHome() throws RemoteException
public Object getPrimaryKey() throws RemoteException
public Handle getHandle() throws RemoteException
public boolean isIdentical(EJBObject obj) throws
RemoteException
public void remove() throws RemoteException, RemoveException
Code example for a remote interface called MyBeanObject:
package myBeans;
import.javax.ejb.*;
import java.rmi.RemoteException;
public interface MyBeanObject extends EJBObject
{
// assume that we have two business logic methods
void processEntry(String firstName, String lastName, int custId)
throws RemoteException;
void deleteEntry(int custId) throws RemoteException;
}
193
15 - ENTERPRISE JAVA BEANS
15.6 client programmer's viewpoint
For an EJB client application, we need to know:
1. how to create or find the bean
2. what methods to use (know its interface)
3. how to release its resources
The client is able to create an EJB through an object implementing the EJBHome interface.
This object acts like a factory for EJBs, creating them for the client application.
The client gains access to the EJB through a remote interface, implemented by an object built
by the EJB host in the deployment process.
Here are the main parts of the client code:
authentication
Client's authentication is done in a way which is server specific. In the case of an web
application, this can be done (for example) through SSL.
getting an initial context
•
if the client is another EJB executing in the same container and the bean to be used is
declared as a resource in the deployment descriptor, the InitialContext is already
available:
Context ctx = new InitialContext();
•
if the client executes outside the container, getting the InitialContext requires the
usage of some server-side properties. Here is an example:
try
{
Properties prop = new Properties();
prop.put(Context.INITIAL_CONTEXT_FACTORY,
"org.jnp.interfaces.NamingContextFactory";
prop.put(Context.PROVIDER_URL,
"localhost:1099");
Context ctx = new InitialContext(prop);
}
194
15 - ENTERPRISE JAVA BEANS
find the home interface of the bean
•
for a client executing inside the container, the code may look like:
Object homeRef = ctx.lookup("java:comp/env/ejb/MyBean");
•
if the client executes outside the container, the bean can be associated to any name in
the JNDI name space. It is JNDI's task to identify the resource associated to the name
provided:
Object homeRef = ctx.lookup("MyBean");
cast the home interface reference
To make sure that the client works with the underlying communication protocol, the client
should use the narrow() method of javax.rmi.PortableRemoteObject:
MyBeanHome myHome = (MyBeanHome)PortableRemoteObject.narrow(homeRef,
MyBeanHome.class);
Why do we have to use the narrow() method? Usually, when we perform a lookup() on a
Context object, the method will return you an Object that needs to be casted to the home interface
we've asked for. Problem is, this cannot be done using the normal/explicit casting:
MyBeanHome myHome = (MyBeanHome)returnedObject
The reason has to do with CORBA. Why? For EJB, the communication between the server and
the client is based on RMI (both remote and local interfaces, in fact, do implements the
java.rmi.Remote interface).
The underlying protocol that it is used for the communication is IIOP (Internet Inter ORB
Protocol), that is part of CORBA standards. It is normally used to describe this communication
system using the Java RMI over IIOP.
IIOP has not been designed for Java, but for generic languages, and this means that there are
some limitations. Some languages, in fact, do not have the concept of casting. Java RMI-IIOP
provides a mechanism to narrow the the Object you have received from your lookup, to the
appropriate type. This is done through the javax.rmi.PortableRemoteObject class and, more
specifically, using the narrow() method.
create an instance of the bean
The instance of the bean is created on the server. The client only has a remote interface to this
instance (i.e., the client has a stub).
195
15 - ENTERPRISE JAVA BEANS
Here is the code:
MyBeanObject myObject = myHome.create();
call business methods on the bean
myObject.processEntry("Dumitrascu", "Vasile", 1102);
remove the bean instance
myObject.remove();
15.7 bean programmer's viewpoint
Since the home interface and the remote interface have been detailed in the previous sections,
we concentrate now on the bean class itself. Besides the implementation of the business methods
(which were declared in the remote interface, as well), the bean class must implement (although
the implementation itself may be empty) a certain set of methods, set which is specific to each
major type of beans (session, entity or message driven).
Assuming that our bean (called MyBean) is a session bean, the code implementing this class
may look like this:
package com.bank11.ccards.ejbeans;
import javax.ejb.SessionContext;
public class MyBean implements javax.ejb.SessionBean
{
public void processEntry(String firstName, String lastName, int
custId)
{
// method implementation
...
}
public void deleteEntry(int custId)
{
// method implementation
...
}
// mandatory methods for session beans
// method implementations may be empty
public void ejbCreate() {}
public void ejbRemove() {}
public void ejbActivate() {}
196
15 - ENTERPRISE JAVA BEANS
public void ejbPassivate() {}
public void setSessionContext(SessionContext ctx) {}
}
15.8 the deployment descriptor
The deployment descriptor of an EJB contains information about the bean in relation to the
application it belongs to.
This information can be divided into two main categories:
•
structural information related to a particular EJB.
•
application assembly information
Although not an exhaustive one, here is a typical list of entries (elements) in a deployment
descriptor:
1. access control entries - security issues; which users can access a bean or a particular
method of a bean
2. bean home name - name under which the bean is registered under JNDI
3. control descriptors - specifies control attributes for transactions
4. EJB class name
5. environment properties
6. the home interface name
7. the remote interface name
8. session specific elements
9. entity specific elements
10. attributes - like transaction, isolation level, security
Keeping in mind that the application assembler is to follow, here is how the deployment
descriptor may look like:
<?xnm version="1.1"?>
<ejb-jar>
<entrprise-beans>
<session>
<ejb-name>CCEnroll</ejb-name>
<home>com.bank11.ccards.ejb.CCEnrollHome</home>
<remote>com.bank11.ccards.CCEnrollObject</remote>
<ejb-class>com.bank11.ccards.CCEnroll</ejb-class>
<session-type>Stateless</session-type>
197
15 - ENTERPRISE JAVA BEANS
<transaction-type>Container<transaction-type>
<ejb-ref>
<ejb-ref-name>ejb/CCAccount</ejb-ref-name>
<ejb-ref-type>Entity</ejb-ref-type>
<home>com.bank11.ccards.ejb.AccountHome</home>
<remote>com.bank11.ccards.ejb.AccountObj</remote>
</ejb-ref>
<security-role-ref>
<description>
This role relates to cash advances from ATMs
</description>
<role-name>CashAdvATM</role-name>
<security-role-ref>
</session>
<entity>
<ejb-name>Account</ejb-name>
<home>com.bank11.ccards.ejb.AccountHome</home>
<remote>com.bank11.ccards.Accountbject</remote>
<ejb-class>com.bank11.ccards.Account</ejb-class>
<persistence-type>Container</persistence-type>
<prim-key-class>java.lang.Integer</prim-key-class>
<reentrant>False</reentrant>
<cmp-field>
<field-name>accountNumber</field-name>
</cmp-field>
<cmp-field>
<field-name>userName</field-name>
</cmp-field>
<cmp-field>
<field-name>customerID</field-name>
</cmp-field>
<cmp-field>
<prim-key-field>accountNumber</prim-key-field>
</cmp-field>
<env-entry>
<env-entry-name>env/minPaymentPerc</env-entry-name>
<env-entry-type>java.lang.Float</env-entry-type>
198
15 - ENTERPRISE JAVA BEANS
<env-entry-value>2.5</env-entry-value>
</env-entry>
</entity>
</enterprise-beans>
</ejb-jar>
The assembly descriptor combines EJBs into a deployable application. Here is a very lean one:
</ejb-jar>
<enterprise-beans>
...
</enterprise-beans>
<assembly-descriptor>
<container-transaction>
<method>
<ejb-name>CCEnroll</ejb-name>
<method-name>*</method-name>
</method>
<trans-attribute>Required</trans-attribute>
</container-transaction>
</assembly-descriptor>
</ejb-jar>
199
16 - session beans
16 - SESSION BEANS
There are two types of session beans, namely stateful and stateless beans.
A stateful session bean preserves data between client accesses. A stateless bean does not.
When an EJB server needs to conserve its resources, it can evict stateful session beans from
memory. This reduces the number of instances maintained by the server. To passivate the bean
and preserve its conversational state, the bean's state is serialized to a secondary storage. When
a client invokes a method on the EJB object, the object is activated, that is, a new stateful
instance is instantiated and populated from the passivated storage.
16.1 container callbacks for session beans
There are 5 mandatory callbacks for classes implementing the SessionBean interface.
public void ejbActivate()
public void ejbPassivate()
public void ejbCreate()
public void ejbRemove()
public void setSessionContext(SessionContext ctx)
The first two methods will never be called for stateless session beans, because the container
will never activate a stateless session bean.
16.2 the life cycle of a stateful session bean
Figure 15.1 illustrates the stages that a session bean passes through during its lifetime. The
client initiates the life cycle by invoking the create() method. The EJB container instantiates the
bean and then invokes the setSessionContext() and ejbCreate() methods in the session
bean. The bean is now ready to have its business methods invoked.
200
16 - session beans
Figure 16.1 Life Cycle of a Stateful Session Bean
While in the ready stage, the EJB container may decide to deactivate, or passivate, the bean by
moving it from memory to secondary storage. (Typically, the EJB container uses a least-recentlyused algorithm to select a bean for passivation.) The EJB container invokes the bean's
ejbPassivate method immediately before passivating it. If a client invokes a business method
on the bean while it is in the passive stage, the EJB container activates the bean, calls the bean's
ejbActivate method, and then moves it to the ready stage.
At the end of the life cycle, the client invokes the remove method, and the EJB container calls
the bean's ejbRemove method. The bean's instance is ready for garbage collection.
Your code controls the invocation of only two life-cycle methods: the create and remove
methods in the client. All other methods in Figure 16.1 are invoked by the EJB container. The
ejbCreate method, for example, is inside the bean class, allowing you to perform certain
operations right after the bean is instantiated. For example, you might wish to connect to a
database in the ejbCreate method.
16.3 the life cycle of a stateless session bean
Because a stateless session bean is never passivated, its life cycle has only two stages:
nonexistent and ready for the invocation of business methods. Figure 16.2 illustrates the stages of
a stateless session bean.
201
16 - session beans
Figure 16.2 Life Cycle of a Stateless Session Bean
202
17 - entity beans
17 - ENTITY BEANS
Entity beans represent actual data (usually, stored in a Database).
The EJB container provides the developer several persistence services:
1. container callbacks to manage caching within a transaction
2. support for concurrent access
3. maintaining a cache between transactions
4. providing all the persistence management code (no SQL code necessary)
There are 2 main types of entity beans.
•
CMPs (Container Managed Persistence)
•
BMPs (Bean Managed Persistence) for which the bean developer provides the actual
persistence (SQL) code
17.1 primary keys
Every entity bean has a primary key. This primary key must be represented by a primary key
class. The requirements that must be satisfied by the primary key are different for the two main
types of entity beans.
For BMPs:
•
the primary key can be any legal RMI/IIOP type
•
it must provide suitable implementations for hashCode(), equals()
•
must have a unique value among beans of a particular type
For CMPs:
•
the container must be able to create a primary key
•
the key class must have a no argument constructor
The fully qualified name of the primary key is always specified in the deployment descriptor
(except when it is not known until deployment)
An example:
<prim-key-class>com.bank11.ccards.CustomerID</prim-key-class>
or
<prim-key-class>java.lang.String</prim-key-class>
203
17 - entity beans
In the case of CMP using a simple type as primary key, the field is specified:
<prim-key-field>sportsTeamID</prim-key-field>
17.2 mandatory callbacks for entity beans
Besides the CRUD callbacks which are discusses later in this section, an entity bean must
implement (although this implementation may be left empty) the following methods:
public void ejbActivate()
public void ejbPassivate()
public void setEntityContext(EntityContext ctx)
public void unsetEntityContext()
CRUD translates through Create, Read, Update and Delete. These methods are mandatory for
entity beans.
17.3 create
When a client calls a create() method on a session bean's home interface, an instance of
that bean is created. On the other side, when a client calls create() on an entity bean's home
interface, state data is stored into data store (usually, a Database) (we actually insert a record in a
database). This is transactional data that is accessible to multiple clients. We can have more
create() methods, all throwing RemoteException, CreateException.
Each create() method from the Home interface of the bean has 2 correspondent methods in
the bean implementation class, namely ejbCreate() and ejbPostCreate(), methods which
have the same parameters, in the same order, as the parameters in the original create()
method.
•
the return type of the ejbCreate() is the same as the primary key, but the developer returns
null for CMP.
•
for BMP, ejbCreate() must have insertion SQL code and returns an instance of the primary
key, not null.
So what is the difference between the ejbCreate() and ejbPostCreate() methods?
ejbCreate() is called before the state of the bean is written to the persistence storage
(database). After this method is completed, a new record (based on the persistence fields) is
created and written. If the Entity EJB is BMP, then this method must contain the code for writing
the new record to the persistence storage.
If you are developing an EJB following 2.0 specs, you can have overloading methods in the
form of ejbCreateXXX(). This will improve the development so you can have different behavior
for creating a bean, if the parameters differs. The only requirement is that for each
ejbCreateXXX() you need to have corresponding createXXX() methods in the home or local
204
17 - entity beans
interface.
ejbPostCreate() is called after the bean has been written to the database and the bean data
has been assigned to an EJB object, so when the bean is available.In an CMP Entity EJB, this
method is normally used to manage the beans' container-managed relationship fields.
17.4 read
•
ejbLoad(), left empty most of the time in CMP, but needs actual SQL code in BMP
•
the bean's persistence implementation may choose to defer loading until it is used
•
ejbLoad() may contain processing code
17.5 update
•
ejbStore() in CMP; the method can be used for preprocessing data to be stored, but in
general, it is empty.
•
in BMP, actual SQL update code; the updated data is to be stored immediately
17.6 delete
•
the corresponding method in the bean implementation class is ejbRemove()
•
data is deleted from DB (in the CMP case), for BMPs, the programmer will create actual
SQL code.
17.7 the life cycle of an entity bean
Figure 17.1 shows the stages that an entity bean passes through during its lifetime. After the
EJB container creates the instance, it calls the setEntityContext() method of the entity bean
class. The setEntityContext() method passes the entity context to the bean.
After instantiation, the entity bean moves to a pool of available instances. While in the pooled
stage, the instance is not associated with any particular EJB object identity. All instances in the
pool are identical. The EJB container assigns an identity to an instance when moving it to the
ready stage.
There are two paths from the pooled stage to the ready stage. On the first path, the client
invokes the create() method, causing the EJB container to call the ejbCreate() and
ejbPostCreate() methods. On the second path, the EJB container invokes the
ejbActivate() method. While an entity bean is in the ready stage, it's business methods can
be invoked.
There are also two paths from the ready stage to the pooled stage. First, a client can invoke the
remove() method, which causes the EJB container to call the ejbRemove() method. Second,
205
17 - entity beans
the EJB container can invoke the ejbPassivate() method.
Figure 17.1 Life Cycle of an Entity Bean
At the end of the life cycle, the EJB container removes the instance from the pool and invokes
the unsetEntityContext() method.
In the pooled state, an instance is not associated with any particular EJB object identity. With
bean-managed persistence, when the EJB container moves an instance from the pooled state to
the ready state, it does not automatically set the primary key. Therefore, the ejbCreate() and
ejbActivate() methods must assign a value to the primary key. If the primary key is incorrect,
the ejbLoad() and ejbStore() methods cannot synchronize the instance variables with the
database. The ejbActivate() method sets the primary key (id) as follows:
id = (String)context.getPrimaryKey();
In the pooled state, the values of the instance variables are not needed. You can make these
instance variables eligible for garbage collection by setting them to null in the
ejbPassivate() method.
206
18 - message-driven beans
18 - MESSAGE-DRIVEN BEANS
18.1 what are the message driven beans?
A message-driven bean is an enterprise bean that allows J2EE applications to process
messages asynchronously. It acts as a JMS message listener, which is similar to an event listener
except that it receives messages instead of events. The messages may be sent by any J2EE
component - an application client, another enterprise bean, or a Web component - or by a JMS
application or system that does not use J2EE technology.
Message-driven beans currently process only JMS messages, but in the future they may be
used to process other kinds of messages.
Session beans and entity beans allow you to send JMS messages and to receive them
synchronously, but not asynchronously. To avoid tying up server resources, you may prefer not to
use blocking synchronous receives in a server-side component. To receive messages in an
asynchronous manner, message-driven bean can be used.
18.2 differences between message-driven beans and the other
ejb's
The most visible difference between message-driven beans and session and entity beans is
that clients do not access message-driven beans through interfaces. Unlike a session or entity
bean, a message-driven bean has only a bean class.
In several respects, a message-driven bean resembles a stateless session bean.
•
•
•
a message-driven bean's instances retain no data or conversational state for a specific
client.
all instances of a message-driven bean are equivalent, allowing the EJB container to
assign a message to any message-driven bean instance. The container can pool these
instances to allow streams of messages to be processed concurrently.
a single message-driven bean can process messages from multiple clients.
The instance variables of the message-driven bean instance can contain some state across the
handling of client messages - for example, a JMS API connection, an open database connection,
or an object reference to an enterprise bean object.
When a message arrives, the container calls the message-driven bean's onMessage() method
to process the message. The onMessage() method normally casts the message to one of the
five JMS message types and handles it in accordance with the application's business logic. The
onMessage() method may call helper methods, or it may invoke a session or entity bean to
process the information in the message or to store it in a database.
A message may be delivered to a message-driven bean within a transaction context, so that all
operations within the onMessage() method are part of a single transaction. If message
processing is rolled back, the message will be redelivered.
207
18 - message-driven beans
18.3 differences between message-driven beans and stateless
session EJBs
Although the dynamic creation and allocation of message-driven bean instances mimics the
behavior of stateless session EJB instances, message-driven beans are different from stateless
session EJBs (and other types of EJBs) in several significant ways:
•
message-driven beans process multiple JMS messages asynchronously, rather than
processing a serialized sequence of method calls.
•
message-driven beans have no home or remote interface, and therefore cannot be
directly accessed by internal or external clients. Clients interact with message-driven
beans only indirectly, by sending a message to a JMS Queue or Topic.
18.4 concurrent support for message-driven beans
Message-driven Beans support concurrent processing for both topics and queues. Previously,
only concurrent processing for Queues was supported.
To ensure concurrency, change the ejb-jar.xml deployment descriptor max-beans-infree-pool setting to >1. If this element is set to more than one, the container will spawn as
many threads as specified. For more information on this element see, max-beans-in-free-pool.
18.5 invoking a message-driven bean
When a JMS Queue or Topic receives a message, call an associated message-driven bean as
follows:
1. Obtain a new bean instance.
Obtain a new bean instance from the connection pool if one already exists, or create a
new one. See Creating and Removing Bean Instances.
2. If the bean cannot be located in the pool and a new one must be created, call the bean's
setMessageDrivenContext() to associate the instance with a container context. The bean
can utilize elements of this context as described in Using the Message-Driven Bean
Context.
3. Call the bean's onMessage() method to perform business logic. See Implementing
Business Logic with onMessage().
Note: These instances can be pooled.
18.6 developing message-driven beans
To create message-driven EJBs, you must follow certain conventions described in the JavaSoft
EJB 2.0 specification, as well as observe several general practices that result in proper bean
behavior.
208
18 - message-driven beans
The EJB 2.0 specification provides detailed guidelines for defining the methods in a messagedriven bean class. The following output shows the basic components of a message-driven bean
class. Classes, methods, and method declarations in bold are required as part of the EJB 2.0
specification:
{
public class MessageTraderBean implements javax.ejb.MessageDrivenBean
public MessageTraderBean() {...};
// An EJB constructor is required, and it must not
// accept parameters. The constructor must not be declared as
// final or abstract.
public void onMessage(javax.jms.Message MessageName) {...}
// onMessage() is required, and must take a single parameter of
// type javax.jms.Message. The throws clause (if used) must not
// include an application exception. onMessage() must not be
// declared as final or static.
public void ejbRemove() {...}
// ejbRemove() is required and must not accept parameters.
// The throws clause (if used) must not include an application
//exception. ejbRemove() must not be declared as final or static.
finalize{};
// The EJB class cannot define a finalize() method
}
18.7 creating and removing bean instances
The EJB container calls the message-driven bean's ejbCreate() and ejbRemove()
methods when creating or removing an instance of the bean class. As with other EJB types, the
ejbCreate() method in the bean class should prepare any resources that are required for the
bean's operation. The ejbRemove() method should release those resources, so that they are
freed before the EJB container removes the instance.
Message-driven beans should also perform some form of regular clean-up routine outside of the
ejbRemove() method, because the beans cannot rely on ejbRemove() being called under all
circumstances (for example, if the EJB throws a runtime exception).
18.8 using the message-driven bean context
The EJB container calls setMessageDrivenContext() to associate the message-driven
bean instance with a container context. This is not a client context; the client context is not passed
along with the JMS message. The EJB container provides the EJB with a container context,
whose properties can be accessed from within the instance by using the following methods from
the MessageDrivenContext interface:
•
getCallerPrincipal()
•
isCallerInRole()
209
18 - message-driven beans
•
setRollbackOnly()- The EJB can use this method only if it utilizes containermanaged transaction demarcation.
•
getRollbackOnly() - The EJB can use this method only if it utilizes containermanaged transaction demarcation.
•
getUserTransaction()- The EJB can use this method only if it utilizes beanmanaged transaction demarcation.
Note: Although getEJBHome() is also inherited as part of the MessageDrivenContext
interface, message-driven EJBs do not have a home interface. Calling getEJBHome()
from within a message-driven EJB instance yields an IllegalStateException.
18.9 implementing business logic with onMessage()
The message-driven bean's onMessage() method performs all of the business logic for the
EJB. The EJB container calls onMessage() when the EJB's associated JMS Queue or Topic
receives a message, passing the full JMS message object as an argument. It is the messagedriven EJB's responsibility to parse the message and perform the necessary business logic in
onMessage().
Make sure that the business logic accounts for asynchronous message processing. For
example, it cannot be assumed that the EJB receives messages in the order they were sent by
the client. Instance pooling within the container means that messages are not received or
processed in a sequential order, although individual onMessage() calls to a given messagedriven bean instance are serialized.
See javax.jms.MessageListener.onMessage() for more information.
18.10 transaction services for message-driven beans
As with other EJB types, message-driven beans can demarcate transaction boundaries either
on their own (using bean-managed transactions), or by having the The EJB container container
manage transactions (container-managed transactions). In either case, a message-driven bean
does not receive a transaction context from the client that sends a message. The EJB container
always calls a bean's onMessage() method by using the transaction context specified in the
bean's deployment descriptor, as required by the EJB 2.0 specification.
Because no client provides a transaction context for calls to a message-driven bean, beans that
use container-managed transactions must be deployed using the Required or NotSupported
attribute in ejb-jar.xml. Transaction attributes are defined in ejb-jar.xml as follows:
<assembly-descriptor>
<container-transaction>
<method>
<ejb-name>MyMessageDrivenBeanQueueTx</ejb-name>
<method-name>*</method-name>
</method>
<trans-attribute>NotSupported</trans-attribute>
</container-transaction>
</assembly-descriptor>
210
18 - message-driven beans
18.11 message receipts
The receipt of a JMS message that triggers a call to an EJB's onMessage() method is not
generally included in the scope of a transaction. For EJBs that use bean-managed transactions,
the message receipt is always outside the scope of the bean's transaction, as described in the
EJB 2.0 specification. For EJBs that use container-managed transaction demarcation, the EJB
container includes the message receipt as part of the bean's transaction only if the bean's
transaction attribute is set to Required.
18.12 message acknowledgment
For message-driven beans that use container-managed transaction demarcation, the EJB
container automatically acknowledges a message when the EJB transaction commits. If the EJB
uses bean-managed transactions, both the receipt and the acknowledgment of a message occur
outside of the EJB transaction context. The EJB container automatically acknowledges messages
for EJBs with bean-managed transactions, but the deployer can configure acknowledgment
semantics using the jms-acknowledge-mode deployment parameter.
18.13 the deployment descriptor
To deploy a message-driven bean on the EJB container, you edit the XML file to create the
deployment descriptors that associate the EJB with a configured JMS destination.
The deployment descriptor for a message-driven bean also specifies:
•
Whether the EJB is associated with a JMS Topic or Queue
•
Whether an associated Topic is durable or non-durable
•
Transaction attributes for the EJB
•
JMS acknowledgment semantics to use for beans that demarcate their own transactions
The EJB 2.0 specification adds the following new XML deployment elements for deploying
message-driven beans.
•
message-driven-destination specifies whether the EJB should be associated with a
JMS Queue or Topic destination.
•
subscription-durability specifies whether or not an associated Topic should be
durable.
•
jms-acknowledge-mode specifies the JMS acknowledgment semantics to use for
beans that demarcate their own transaction boundaries. This element may have two
values: AUTO_ACKNOWLEDGE (the default) or DUPS_OK_ACKNOWLEDGE.
These elements are defined in the ejb-jar.xml deployment file, as described in the EJB 2.0
specification. The following excerpt shows a sample XML stanza for defining a message-driven
bean:
<enterprise-beans>
211
18 - message-driven beans
<message-driven>
<ejb-name>exampleMessageDriven1</ejb-name>
<ejb-class>examples.ejb20.message.MessageTraderBean</ejb-class>
<transaction-type>Container</transaction-type>
<message-driven-destination>
<jms-destination-type>
javax.jms.Topic
</jms-destination-type>
</message-driven-destination>
...
</message-driven>
...
</enterprise-beans>
In addition to the new ejb-jar.xml elements, the weblogic-ejb-jar.xml file includes a
new message-driven-descriptor stanza to associate the message-driven bean with an actual
destination in the EJB container.
18.14 the life cycle of a message-driven bean
Figure 15.4 illustrates the stages in the life cycle of a message-driven bean.
The EJB container usually creates a pool of message-driven bean instances. For each instance,
the EJB container instantiates the bean and performs these tasks:
1. It calls the setMessageDrivenContext method to pass the context object to the
instance.
2. It calls the instance's ejbCreate method.
Figure 15.4 Life Cycle of a Message-Driven Bean
Like a stateless session bean, a message-driven bean is never passivated, and it has only two
states: nonexistent and ready to receive messages.
At the end of the life cycle, the container calls the ejbRemove() method. The bean's instance
is then ready for garbage collection.
212