Sun Java System Application Server Enterprise Edition 8.1 2005Q2 Upgrade and Migration Guide

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# J2EE Application Components

J2EE simplifies development of enterprise applications by basing them on standardized, modular components, providing a complete set of services to those components, and handling many details of application behavior automatically, without complex programming. J2EE v1.4 architecture includes several component APIs. Prominent J2EE components include:

- Client Application

- Web Application

- Enterprise JavaBean (EJB)

- Connector

- Enterprise Application Archive (EAR)

J2EE components are packaged separately and bundled into a J2EE application for deployment. Each component, its related files such as GIF and HTML files or server-side utility classes, and a deployment descriptor are assembled into a module and added to the J2EE application. A J2EE application is composed of one or more enterprise bean(s), Web, or application client component modules. The final enterprise solution can use one J2EE application or be made up of two or more J2EE applications, depending on design requirements.

A J2EE application and each of its modules has its own deployment descriptor. A deployment descriptor is an XML document with an .xml extension that describes a component’s deployment settings.

A J2EE application with all of its modules is delivered in an Enterprise Archive (EAR) file. An EAR file is a standard Java Archive (JAR) file with an .ear extension. The EAR file contains EJB JAR files, application client JAR files and/or Web Archive (WAR) files.

The migration process is concerned with moving J2EE application components, modules, and files. For more information on migrating various J2EE components, refer to Chapter 6, Migrating from Application Server 6.x/7.x to Application Server 8.1.

For more information on J2EE, see:

- J2EE 1.4 tutorial

- J2EE overview

- J2EE website

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