Download Enterprise Java Beans Lecture Stucture

Enterprise Java Beans
Mikael Åkerholm
Component Technologies
EJB
Page 1, 5-Nov-03
Lecture Stucture
Introduction
1.
Java
2.
JavaBeans
3.
J2EE
J2EE
1.
EJB
2.
Java Serverlets, JSP, and clients
3.
Packaging and Deployment
Summary, Questions
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EJB
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1
References
Literature:
z
Enterprise JavaBeans, R.M. Haefel, 3rd O’Reilly 2001
z
The Source for Java Technology, good, up to date,
tutorials, specifications, and reference implementations
http://java.sun.com/
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EJB
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Java
‰ The current main release is the Java 2 platform, it is
modular and include three parts:
z
J2SE, Java 2 Platform, Standard Edition
)provides the essential compiler, tools, runtimes, and APIs for writing,
deploying, and running applets and applications
z
J2EE, Java 2 Platform, Enterprise Edition
)component based model, simplifies enterprise development and
deployment; manages the infrastructure and supports the web services to
enable development business applications
z
J2ME, Java 2 Platform, Micro Edition
)a highly optimized Java runtime environment, specifically addresses the
vast consumer space (embedded systems), from smart cards to more PC
like applications
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2
JavaBeans
‰ A desktop component model for Java, included among
the J2SE technologies
‰ A Java API and a Specification
‰ Software reuse for Software Development
‰ Object-Oriented
‰ Focus on lightweight components for small-scale CBD
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EJB
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JavaBeans
‰ Use standard naming conventions
‰ Have public interfaces
‰ Packaged in JAR files
‰ Interface composed of:
z
Properties:
)Simple, Boolean or Indexed
)Could be Bound or Constrained
z
Events:
)signaled by changing properties
)signaled for custom state changes
z
Methods:
)default is any public method
)Built via BeanInfo class or Reflection API
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Java 2 Enterprise Edition (J2EE)
‰ For enterprise applications (distributed business
applications)
z
Demands
)Availability
)Security
)Reliability
)Scalability
z
From the early 90s
)Shift from 2-tier, client-server application models to more flexible 3-tier (and n-tier)
application models
)The new models separated business logic from system services and the user interface
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EJB
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Java 2 Enterprise Edition (J2EE)
Presentation
Presentation
Presentation tier
Tier Boundary
Business
Business
logic
logic
Business
Business
logic
logic
Business tier
Database
Database
driver
driver
Tier Boundary
Database
Database
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EJB
Data tier
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Java 2 Enterprise Edition (J2EE)
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EJB
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Java 2 Enterprise Edition (J2EE)
‰ J2EE Application Programming Model
z
Applications on the client
z
Java Server Pages (JSP), web components on the server,
extension of Serverlets; in the end these are concerned with
clients
z
EJB, business components on the server side
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EJB
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Enterprise JavaBean (EJB)
‰ Java’s component model for distributed enterprise
applications, released 1998
‰ EJB technology defines a model for the development of
reusable Java server components
‰ Def:
”Enterprise Java Beans is a standard server-side component
for computer transaction monitors.”
‰ Applications written using EJB are:
z
Scalable
z
Transactional
z
Multi-User secure
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EJB != JB
‰ Once and for all
‰ JB
z
Desktop Components
‰ EJB
z
Enterprise Distributed Components
z
Could of course be implemented using JavaBeans
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EJB
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J2EE
Component Technologies
EJB
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Contents
1.
EJB Components
‰ General
‰ Interfaces and classes
‰ Architechture
‰ Different types
‰ Transactions
2.
Java Serverlets, JSP and clients
‰ Brief
3.
Packaging and Deployment
‰ Brief
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What is an Enterprise JavaBean?
”A server-side component that
encapsulates the business logic of an
application”
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EJB
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When to use Enterprise JavaBeans
If any of these requirements hold for your
application:
‰ The application must be scalable and
distributable
‰ Transactions are required to ensure data
integrity
‰ The application will have a variety of clients
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Enterprise JavaBeans
‰ Entity Beans
z
Persistent
z
Primary key
‰ Session Beans
z
Receive their state from the client
z
Live as long as the client need them
‰ Message-Driven Beans (EJB 2.0)
z
Asynchronously
z
Only a bean class – no interfaces
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Classes and Interfaces
‰ Remote Interface
Specifies the beans business methods
‰ Home Interface
Defines the beans life cycle methods
‰ Bean Class
Implements the beans business methods
‰ Primary Key
Provides a pointer into the database
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A Bean’s interfaces
‰ Remote Interface
z
Business methods to do the beans work
z
Implemented by the “shadowdy” Bean Object
‰ Remote Home Interface
z
Defines the beans life cycle methods
z
Implemented by EJB Home
‰ Local Interface (EJB 2.0)
z
Business methods used by other beans in the same
container
‰ Local Home Interface (EJB 2.0)
z
Life-cycle methods used by other beans in the same
container
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A Bean’s classes
‰ The Bean Class
z
Implement the business methods
z
Do not implement Remote (or local) and (local) Home
Interfaces
z
Beans exist in the middle of client software and data
sources
z
Clients never interact directly with the bean class, uses
methods of the Remote and Home Interface, interacting
with automatically generated stubs
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EJB
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EJB Architecture
Home Interface
EJB Client
EJB Server
Home
Home
Stub
Stub
EJB Container
Home
Home
Object
Object
Object
Object
Stub
Stub
EJB
EJB
Object
Object
Bean
Bean
Class
Class
Remote Interface
(or Local Interface)
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EJB
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When to use Entity Beans
‰ The bean represents a business entity, not a
procedure
‰ To provide a safe and consistent interface to a set of
shared data
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Entity Beans
‰ Represents a business object in a persistent
storage mechanism
‰ Can be shared by multiple clients
‰ Two types of persistence:
z
Container-managed
z
Bean-managed
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Container-managed persistence
‰ They are the simplest to develop
‰ The bean’s code contain no database access
calls
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Bean-managed persistence
‰ Explicitly write persistence logic
‰ More flexibility in how state is managed between
the bean instance and the database
‰ Used when deployment tools are inadequate
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Life Cycle
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When to use Session Beans
‰ Only one client has access to the beans instance
‰ Non persistent and existing only for a short period of
time
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Session Beans
‰ Useful for describing interactions
‰ Does not represent shared data in the database,
but can access shared data
‰ Two types:
z
Stateless
z
Stateful
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Stateless Session Beans
‰ Supports multiple clients
‰ Relatively easy to develop and very efficient
‰ Require few server resources
Stateless session beans are appropriate if:
‰ The bean's state has no data for a specific client
‰ A generic task is performed in a single method
invocation
‰ The bean fetches a set of read-only data
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EJB
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Life Cycle
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Stateful Session Beans
‰ Dedicated to one client for the life of the bean
instance
‰ Instance variables represent the state of a unique
client-bean session
Stateful session beans are appropriate if:
‰ The bean needs to hold information about the
client across method invocations
‰ The bean mediates between the client and the
other components of the application
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EJB
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Life Cycle
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EJB
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When to use Message-Driven Beans
‰ To receive messages asynchronously
‰ When consuming JMS messages
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EJB
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Message-Driven Beans
‰ Has only a bean class
‰ Can consume and process messages
concurrently
‰ Acts as a JMS message listener
‰ Deliver messages to a virtual channel
‰ Currently process only JMS messages
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EJB
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Life Cycle
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EJB
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Calling an EJB
2 Return
reference
home stub
JNDI
1 Ask for
Home object
5 Return Obj stub
EJB Client
3 Ask for EJB Object
EJB Server
EJB Container
Home
Home
Object
Object
4 Create EJB Object
EJB
EJB
Object
Object
6 Invoke a method
Bean
Bean
Class
Class
7 Wraps the call to the Bean Class
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EJB
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Transactions with EJBs
‰ Managed automatically
‰ No use of API
‰ Defined at deployment
‰ Possible to explicitly manage transactions but not
recommended
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EJB
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A Transaction
‰ Transactions is the execution of a unit-of-work that
accesses on or more resources, usually databases
‰ A unit-of-work is a set of activities that relate to each
other and must be completed together
‰ The objective with transactions is to execute an unit-of
work that results in a reliable exchange
‰ Transactions are often complex and usually involve
manipulation of data
‰ Transactions must work perfectly every time or not be
executed at all
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Acid-properties
‰ Atomic
z
A transaction must execute completely or not at all
‰ Consistent
z
A transaction always leads to a correct transformation of
the system state by preserving the state invariance
‰ Isolated
z
The data a transaction access cannot be affected by any
other parts of the system until the transaction is
completed
‰ Durable
z
All the data changes made during the course of
transaction must be written to a physical storage before
the transactions is physically completed
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EJB
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Transaction Management
‰ Declarative transaction management
z
The transactional behavior controls by using
transactions attribute in the deployment descriptor
z
One of the primary advantages of EJB
z
Reduce the complexity for the developers
z
Makes it easier to create robust transaction applications
‰ Explicit transaction management
z
Difficult to use
z
Will not be covered in this talk
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Transactions Attribute
‰ You can set the runtime transaction attribute as a XMLattribute in the deployment descriptor by hand, but we
will use a deployment wizard
‰ It is more efficient and easier to use transaction
attributes than to control transactions explicitly
‰ It is possible to set a transaction attribute for the entire
bean or to set different transactions attribute for
individual methods
‰ There exist six transaction attributes in EJB 2.0:
z
NotSupported
z
Supports
z
Required
z
RequiresNew
z
Mandatory
z
Never
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EJB
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The Different Transactions Attributes
‰ NotSupported
z
Invoking a method on a bean with this transaction
attribute suspends the transactions until the method is
completed
‰ Supports
z
Means that the bean method will be included in the
transactions scope if it is invoked within a transaction
‰ Required
z
Means that the bean method must be invoked within the
scope of a transaction
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The Different Attributes, Cont.
‰ RequiresNew
z
Means that a new transactions always starts
‰ Mandatory
z
Means that the bean method must always be made part
of the transaction scope of the calling client
‰ Never
z
Means that the bean method must never be invoked
within the scope of a transaction
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EJB
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Java Serverlets, JSP and clients
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EJB
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Serverlets
‰ A serverlet is a server side component, which is
deployed in the same fashion as a EJB
‰ Used to dynamically create html pages, for clients
z
Since it is server side, it extends the reach for clients to
backend components (e.g., EJBs) in the server
‰ A servelet is assigned to handle an access for a specific
html page
z
When the specific page is requsted by a browser, a
method in the servelet is envoked which posts the html
page back
‰ When a client looks at the html code posted from the
server, it looks just like a static html page
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EJB
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JavaServer Pages, JSP
‰ An extension of serverlets, simplifies the creation of
dynamic html
‰ Simply lets the developer incorporate real java code into
a html page when desired (as a scripting language)
‰ Is actually compiled to servelets
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EJB
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Clients
‰ Web clients with serverlets or JSP, JSP possibly more
powerful
‰ Can also create application clients
z
An client side component, that access EJBs
z
Easy and straightforward to create, deploted in the same
fashion as EJBs
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EJB
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Packaging and Deployment
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EJB
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Deployment and Deploy Tools
‰ Packaging
z
Create JAR files
)A compressed platform-independent file
)Bean and Beans interface and help classes
z
Create deployment descriptors
)XML files specifying
)Access control
)Bean references
)External Resource references
)Transactional attributes
‰ Deployment
z
Deploy the application on a server
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EJB
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Packaging and Deployment
‰ Can be done by hand
z
Gives full control
z
Time consuming
‰ Graphical deplytool with wizards included in the
reference implementation
z
Easy, fast
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EJB
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Summary
‰ JB != EJB
‰ EJBs Typically used for 3 or more tiers bussiness
applications
‰ EJBs, server side components, with remote and home
interfaces; packaged in JAR files with deployment
descriptors
z
Session, Entity, Message
‰ Clients, can be applications or web pages through
servelets or JSP
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EJB
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Example
Entity Bean Person
“Let’s look how to build a bean”
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EJB
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The Remote Interface
/**
Remote Interface
Business methods for Person beans
*/
import javax.ejb.Exception;
javax.ejb.Exception;
public interface Person extends javax.ejb.EJBObject {
String getName()
getName() throws RemoteException;
RemoteException;
void setName(String n) throws RemoteException;
RemoteException;
}
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EJB
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The Home Interface
/**
Home Interface
Life cycle method for Person beans
*/
import
import
import
java.rmi.RemoteException;
java.rmi.RemoteException;
javax.ejb.CreateException;
javax.ejb.CreateException;
javax.ejb.FinderException;
javax.ejb.FinderException;
public interface PersonHome extends javax.ejb.EJBHome {
//responsible for initalizing an instance of the bean
public Person create(int id)
throws CreateException,
CreateException, RemoteException;
RemoteException;
//look up a bean in a DB
public findByPK(PersonPK pk)
pk)
throws FinderException,
FinderException, RemoteException;
RemoteException;
}
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The Bean Class
/**
Bean Class
Implements the business
Person Bean is a Entity
*/
public class PersonBean
methods for Person component
Bean
implements javax.ejb.EntityBean {
private int id;
private String name;
//business methods
public Sting getName()
getName() {
return name;
}
public void setName(String n) {
name=n;
}
// continue next slide…
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Page 55, 5-Nov-03
// … and the bean class continues
//ejb.entity
//ejb.entity methods
public PersonPK ejbCreate(int i) {
id=i;
return null;
}
public
public
public
public
public
public
public
public
void
void
void
void
void
void
void
void
ejbPostCreate(int i) {/*+*/}
ejbSetEntityContext(EntityContext ctx)
ctx) {}
ejbUnsetEntityContext()
ejbUnsetEntityContext() {/*+*/}
ejbActivate()
ejbActivate() {}
ejbPassivate()
ejbPassivate() {}
ejbLoad()
ejbLoad() {/*+*/}
ejbStore()
ejbStore() {/*+*/}
ejbRemove()
ejbRemove() {}
// + note: session beans do not have these methods
}
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Example
Simple JSP page
“How to build a web client”
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<%-<%-- A jsp file that use a session bean --%>
--%>
<%@ page import="Converter,ConverterHome,javax.ejb.*,
import="Converter,ConverterHome,javax.ejb.*, java.math.*,
java.math.*,
javax.naming.*,
javax.naming.*, javax.rmi.PortableRemoteObject,
javax.rmi.PortableRemoteObject,
java.rmi.RemoteException"
java.rmi.RemoteException" %>
<%!
private Converter converter = null;
null;
<%-<%-- The init method,
method, JNDNI lookup --%>
--%>
public void jspInit()
jspInit() {
try {
InitialContext ic = new InitialContext();
InitialContext();
Object objRef = ic.lookup("java:comp/
ic.lookup("java:comp/env/
env/ejb/
ejb/TheConverter");
TheConverter");
ConverterHome home =
(ConverterHome)PortableRemoteObject.narrow(objRef,ConverterHome.c
lass);
lass);
converter = home.create();
home.create();
} catch (Exception ex) {
System.out.println("Couldn't create converter bean."+
bean."+
ex.getMessage());
ex.getMessage());
}
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public void jspDestroy()
jspDestroy() {
converter = null;
null;
}
%>
<html>
<form method="get">
method="get">
<input type="text"
type="text" name="amount"
name="amount" size="25">
<input type="submit"
type="submit" value="Submit">
value="Submit"> </form>
<%
String amount = request.getParameter("amount");
request.getParameter("amount");
if ( amount != null && amount.length()
amount.length() > 0 ) {
BigDecimal d = new BigDecimal (amount);
amount);
%>
<%= amount %> Kronor are <%= converter.yenToEuro(d)
converter.yenToEuro(d) %>
Euro.
<%
}
%>
</body
>
</body>
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</html>
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EJB
Example
A deployment descriptor
“Good to understand, when time allows!”
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XML Document Header
XML documents start with two general information tags:
1. Specifies the XML version the file use
z
<?xml version=”1.0”?>
2. Specifies the DTD that defines the XML file
z
Provides the URL to the DTD, you can download it and
validate the XML file
z
<!DOCTYPE ejb-jar PUBLIC ”-//Sun Microsystems,
Inc.//DTD Enterprise JavaBean 1.1//EN”
”http://java.sun.com/j2ee/dtds/ejb-jar.dtd”>
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XML Descriptor’s Body
The Body start with a root element defined by the DTD.
‰ The root element describing:
z
Bean/ Beans <enterprise-beans>
)Entity or Session Beans
)Primary Key
)Environment Entries
)Reference to other Beans
)Reference to External Resources (such as a Database)
)Security Roles
z
Bean/Beans Assembly <assembly-description>
)Transactional attributes
)Security roles & Method permissions
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XML Body example
<ejb<ejb-jar>
<description>a body example</description>
<enterprise<enterprise-bean>
<session>
- - </session>
<entity>
- - </entity>
- - </enterprise</enterprise-bean>
<assembly<assembly-descriptor>
- - </assembly</assembly-descriptor>
</ejb</ejb-jar>
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XML Bean example
<entity>
<description> a Bean example </description>
<ejb</ejb-name>
<ejb-name>PlayerBean
name>PlayerBean</ejb
<home>com.chess.player.PlayerHome
</home>
<home>com.chess.player.PlayerHome</home>
<remote>com.chess.player.Player</remote>
<ejb-class>
<ejb-class> com.chess.player.PlayerBean</ejb
com.chess.player.PlayerBean</ejb<persistence<persistence-type>Container</persistencetype>Container</persistence-type>
<prim<prim-keykey-class>java.lang.Integer</primclass>java.lang.Integer</prim-keykey-class>
<primkey-field>
primkey-field>id</primkey
field>id</primkey<reentrant>False</reentrant>
<cmp-field>
cmp-field><fieldfield><field-name>id</fieldname>id</field-name></cmp
name></cmp- - <cmp-field>
cmp-field><fieldfield><field-name>name</fieldname>name</field-name></cmp
name></cmp</entity>
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XML Security Roles and Method permissions
<ejb-jar>
<enterprise-beans>...</enterprise-beans>
…
<assembly-descriptor>
<container-transaction> … </container-transaction>
<security-role>
<description>allows to read/write</description>
<role-name>everyone</role-name>
</security-role>
<method-permission>
<role-name>everyone</role-name>
<method>
<ejb-name>myBean</ejb-name>
<method-name>*</method-name>
</method>
</method-permission>
</assembly-descriptor>
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