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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.

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Building Web Applications With J2EE

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

  2. AssumptionsAudience Background Elementary knowledge of J2EE Currently planning or in the process of building Web applications with J2EE

  3. 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

  4. 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

  5. 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.

  6. 1985-1992 • One programming language for building distributed (client-server) applications • IDE for compilation, debugging, execution and file management • Procedural programming

  7. 1990+ • VB brings client-server (distributed) application development environment to desktops • Procedural programming • GUI development is more user-friendly

  8. 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

  9. 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.

  10. 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

  11. 2000+ • Enthusiastic software developers start using J2EE. • Container Managed Persistence becomes a reality • Methodologies for writing J2EE applications are discovered.

  12. 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.

  13. 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

  14. 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

  15. 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.

  16. Servicing a request Http request originates in a browser URL Presentation-tier Business-tier Http response ends in the browser

  17. J2EE Patterns: Presentation-tier • Front Controller • View Helper • Composite View • Service To Worker • Dispatcher View

  18. 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 <servlet-mapping> <servlet-name>TheViewController</servlet-name> <url-pattern>*.ctrl</url-pattern> </servlet-mapping>

  19. 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

  20. Service To Worker URL Business-tier

  21. Value Object Business Delegate EJB Requests EJB/Business Service Locates Business Service Service Locator Processing the request URL

  22. J2EE Patterns: Business-tier • Business Delegate • Value Object • Session Façade • Composite Entity • Value Object Assembler • Value List Handler • Service Locator

  23. 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.

  24. J2EE Patterns for Servicing Requests Presentation-tier Business-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

  25. 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

  26. Package Structure • Business Functionality code • extends framework code • Framework code • implementation of patterns

  27. 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

  28. 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.

  29. Q & A

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