Once we have our components assembled into the appropriate modules, each with a deployment descriptor, we can assemble an application by bundling the component modules along with an application deployment descriptor into an enterprise application archive (ear) file.
Like component modules, an application archive is just a jar file with files stored in specific locations, as dictated by the J2EE specifications. The deployment descriptor is stored as META-INF/application.xml in the jar file, and component modules are placed in the jar and referenced in the application descriptor using their location relative to the top of the application archive. The full syntax of the application deployment descriptors can be found in Appendix A.
Application deployment descriptors are simpler in structure, because they primarily serve to assemble component modules that have their own deployment information. The application deployment descriptor contains the following categories of information:
Similar to component modules, applications can also have descriptive information in their deployment descriptors. The application can be given a name and a description that can be displayed in management tools, for example.
Figure 2-5. Web module deployment descriptor
Each component module to be included in the application must be referenced ...