Java Enterprise in a Nutshell, Third Edition

Component Modules

A component module is the smallest unit of deployment in the J2EE deployment model. A module is simply a jar file containing all of the bits and pieces that define a set of components. Each module contains components of the same type so that they can be easily delegated to the containers that handle them.

Module Jar Files

Each component module is packaged as a jar file with a specific layout for the elements that make up the components. Table 2-2 summarizes the different module jar files and deployment descriptors used for the different J2EE component types:

Table 2-2. Component module format summary

Component type	Module jar file suffix	Deployment descriptor filename and location
Web	.war(“web archive”)	WEB-INF/web.xml
Enterprise JavaBeans	.jar	META-INF/ejb-jar.xml
Applet	.jar	Not applicable
Application client	.jar	META-INF/application-client.xml
Resource adapter	.rar (“resource archive”)	META-INF/rar.xml

In addition to the deployment descriptor locations specified Table 2-2, each component module jar file also has a specific file layout that’s required for the elements that make up the components. In a war file, for example, all individual class files included in the module must be placed in the WEB-INF/classes directory, all class libraries are placed in the WEB-INF/lib directory, and so on.

Deployment Descriptors

Each component module (except for applet jar files) includes a standard J2EE deployment descriptor. These descriptors are key to the assembly and deployment ...