Download Building Web Applications With J2EE

Building Web Applications
With J2EE
By Sandeep Dixit, Partner
Ohioedge
Enterprise Java Solutions Provider
Since 1996
Assumptions
Audience Background
Elementary knowledge of J2EE
Currently planning or in the process of
building Web applications with J2EE
Assumptions
Audience Expectations
Want to learn or verify essential concepts
of Web application development with
J2EE
Want to see live demonstrations of
– sample applications
– deploying sample applications in J2EE-compliant
application server
– how a proper implementation of these concepts results in
robustness, quality, and improved productivity
Today’s Agenda
–
–
–
–
–
–
Origin of J2EE
Mindset for building Web applications
Generalization: J2EE Patterns
Three-tier component: EJB-JavaBean-JSP
XML schema-driven applications
Directory structure: Effective organization of java,
jsp, xml, sql and bat script files
– Package structure: Effective grouping of Java and
JSP source code
– Live Demonstration of J2eeBuilder Framework &
component plug-in
J2EE Facts
J2EE is not a programming language.
J2EE is a specification for writing enterprise
applications (distributed computing)
J2EE specification compliant code is
portable between J2EE-compliant
application servers.
1985-1992
• One programming language for building
distributed (client-server) applications
• IDE for compilation, debugging,
execution and file management
• Procedural programming
1990+
• VB brings client-server (distributed)
application development environment to
desktops
• Procedural programming
• GUI development is more user-friendly
1995+
• Java, an OS independent, pure Objectoriented, programming language starts
gaining ground
• Object-oriented programming is more
user friendly
• Java Remote Method Invocation (RMI) is
made available for distributed computing
1997+
• Apache Web Server becomes de-facto
web server
• Java RMI is further strengthened by a
specification - J2EE specification - on
how to write an RMI server.
• Developing distributed applications is
made more user friendly.
1999+
• Servlet/JSP makes HTML-based Web GUI
a real thing for enterprise applications
• Object-oriented programming is further
extended into XML definition driven
object-oriented programming
• J2EE incorporates XML as the way to
specify data
2000+
• Enthusiastic software developers start
using J2EE.
• Container Managed Persistence becomes
a reality
• Methodologies for writing J2EE
applications are discovered.
2001+
• Various articles, papers, and books on
J2EE Patterns, Practices, and Strategies
are published and presented
• Jboss an open-source J2EE 1.3-compliant
application server is used by more than 1
Million developers world-wide
• J2EE is free. J2EE is open. J2EE is here
to stay.
Mindset for building Web
applications
CRM
Application
Server
• Think in terms of “Servicing a request”
• For example, a click on a “create” button
on a “customer” page in a browser is a
request.
• Building a Web application requires an
approach of handling and processing http
requests and sending appropriate
responses back to the requesters
Generalization of Services
• Generalization of how http requests are
serviced by presentation-tier, middle-tier,
and data-tier results in a generic, intertier dependent, reusable library of source
code - J2EE patterns
Generalization of Services
•
For an example, the application processing “customer-create”
request needs to verify if the requester is valid, requester’s session is
valid, and license to use application itself is valid. These validation
steps are independent of “customer-create” request and are
applicable to any requests such as, “customer-delete”, “contact-find”,
etc.
•
This requires that every time a request is received it should be first
passed-on to a “generic validation service” that would either permit
or deny further servicing of the request.
•
Typically, validation service would get categorized under
“presentation services”. Depending upon the layer where the services
are called, they would be categorized under either - presentation,
business, or data services.
Servicing a request
Http request originates in a browser
URL
Presentation-tier
Business-tier
Http response ends in the browser
J2EE Patterns: Presentation-tier
• Front Controller
• View Helper
• Composite View
• Service To Worker
• Dispatcher View
Brief overview of
Presentation-tier patterns
• Front Controller: Provides a centralized controller for
managing the handling of a request
<servlet-mapping>
<servlet-name>TheViewController</servlet-name>
<url-pattern>*.ctrl</url-pattern>
</servlet-mapping>
• View Helper: Encapsulates logic that is not related to
presentation formatting into Helper components
Brief overview of
Presentation-tier patterns
•
Dispatcher View: Similar to Service To Worker; Dispatcher plays a limited role
in the processing of requests - Dispatcher plays limited to moderate role in
view management.
–
–
•
Limited role: No outside resources are utilized in order to choose the view. The information
encapsulated in the request is sufficient to determine the view to dispatch the request. For
example: http://my.server.com/myContextRoot/Controller?next=login.jsp
Moderate role: The information contains an action to be completed:
http://my.server.com/myContextRoot/Controller?action=login The responsibility of the
dispatcher component here is to translate the logical name ‘login’ into the resource name of an
appropriate view, such as ‘login.jsp’, and dispatch to that view. To accomplish this translation, the
dispatcher may access resources such as an XML configuration file that specifies the appropriate
view to display.
Service To Worker: Combines a Dispatcher component with the Front
Controller and View Helper patterns - Dispatcher plays moderate to large
role in view management. Dispatcher is more sophisticated. The dispatcher
may invoke a business service to determine the appropriate view to display.
–
For example: http://my.server.com/myContextRoot/Customer.ctrl?submit=Set
Service To Worker
URL
Business-tier
Processing the request
URL
Value
Object
Business
Delegate
Requests EJB/Business
Service
Service
Locator
EJB
Locates
Business
Service
J2EE Patterns: Business-tier
• Business Delegate
• Value Object
• Session Façade
• Composite Entity
• Value Object Assembler
• Value List Handler
• Service Locator
Brief overview of Business-tier
patterns
• Business Delegate: De-couples presentation and service tiers,
and provides a façade and proxy interface to the services.
• Value Object: Facilitates data exchange between EJB and
BusinessDelegate
• Value List Handler: Manages query execution, results caching,
and results processing.
• Service Locator: Encapsulates complexity of business service
lookup and creation; locates business service factories.
J2EE Patterns for Servicing
Requests
Presentation-tier
Business-tier
Data-tier
• Front Controller
• Business Delegate
• Service Activator
• View Helper
• Value Object
• Data Access Object
• Composite View
• Session Façade
• Service To Worker • Composite Entity
• Dispatcher View
• Value Object Assembler
• Value List Handler
• Service Locator
Directory Structure
• Source Code
• Scripts
• J2EE Specification Code
– ejb.xml
– web.xml
– application.xml
• J2EE Application Specific Code
– jboss.xml
– jboss-web.xml
• Java/Jar Specific Code
– manifest.mf
Package Structure
• Business Functionality code
– extends framework code
• Framework code
– implementation of patterns
J2eeBuilder Framework
• Demonstration of a framework
– Implementation of patterns
– Session Management
– User Management
– License Management
– j2eebuilder-config.xml
• Demonstration of plugging-in a “product” component
into the framework
Summary
•
J2EE is Java, EJB specification, Servlet, JSP, Html, and XML
•
Use open-source software such JDOM, LOG4J, Apache Web Server,
Tomcat Servlet Container, and JBoss Application Server
•
Document your architecture, data-structure, functional scope,
directory structure, and package structure, before launching a fullscale development
•
Understand key concepts. Learn to do-it by hand using simple
TextPad before using IDEs.
•
Keep it J2EE compliant. Avoid getting locked into any vendor specific
technology.
•
You build a generic framework and robustness, quality and
productivity will come.
Q&A