Building Web Applications With J2EE

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Building Web Applications With J2EE
By Sandeep Dixit, Partner
Ohioedge Enterprise Java Solutions Provider
Since 1996
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AssumptionsAudience Background

• Elementary knowledge of J2EE
• Currently planning or in the process of building
  Web applications with J2EE

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AssumptionsAudience 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

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Todays 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

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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.

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1985-1992

• One programming language for building distributed
  (client-server) applications
• IDE for compilation, debugging, execution and
  file management
• Procedural programming

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1990

• VB brings client-server (distributed) application
  development environment to desktops
• Procedural programming
• GUI development is more user-friendly

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1995

• Java, an OS independent, pure Object-oriented,
  programming language starts gaining ground
• Object-oriented programming is more user friendly
• Java Remote Method Invocation (RMI) is made
  available for distributed computing

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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.

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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

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2000

• Enthusiastic software developers start using
  J2EE.
• Container Managed Persistence becomes a reality
• Methodologies for writing J2EE applications are
  discovered.

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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.

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Mindset for building Web applications
Application Server
CRM

• 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

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Generalization of Services

• Generalization of how http requests are serviced
  by presentation-tier, middle-tier, and data-tier
  results in a generic, inter-tier dependent,
  reusable library of source code - J2EE patterns

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Generalization of Services

• For an example, the application processing
  customer-create request needs to verify if the
  requester is valid, requesters 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.

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Servicing a request
Http request originates in a browser
URL
Presentation-tier
Business-tier
Http response ends in the browser
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J2EE Patterns Presentation-tier

• Front Controller
• View Helper
• Composite View
• Service To Worker
• Dispatcher View

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Brief overview of Presentation-tier patterns

• Front Controller Provides a centralized
  controller for managing the handling of a request
• View Helper Encapsulates logic that is not
  related to presentation formatting into Helper
  components

ltservlet-mappinggt ltservlet-namegtTheViewContro
llerlt/servlet-namegt lturl-patterngt.ctrllt/url-p
atterngt lt/servlet-mappinggt
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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/Contro
  ller?nextlogin.jsp
• Moderate role The information contains an action
  to be completed http//my.server.com/myContextRoo
  t/Controller?actionlogin 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/Cu
  stomer.ctrl?submitSet

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Service To Worker
URL
Business-tier
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Processing the request
URL
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J2EE Patterns Business-tier

• Business Delegate
• Value Object
• Session Façade
• Composite Entity
• Value Object Assembler
• Value List Handler
• Service Locator

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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.

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J2EE Patterns for Servicing Requests
Business-tier
Presentation-tier
Data-tier

• Front Controller
• View Helper
• Composite View
• Service To Worker
• Dispatcher View

• Business Delegate
• Value Object
• Session Façade
• Composite Entity
• Value Object Assembler
• Value List Handler
• Service Locator

• Service Activator
• Data Access Object

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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

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Package Structure

• Business Functionality code
• extends framework code
• Framework code
• implementation of patterns

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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

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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 full-scale
  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.

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Q A