Section 3.1. WARs Versus EARs

3.1. WARs Versus EARs

The WAR file is a convenient way to bundle up all pieces of a web application. All servlet containers know how to deploy a WAR filethey expand the bundle, look for the WEB-INF directory, and read the web.xml found there for further deployment instructions.

The EAR file provides the same type of functionality for a full-fledged J2EE application. JBoss expands the EAR, finds the required deployment descriptors, and proceeds from there.

An EAR is like a carton of eggsit keeps everything organized. While the carton doesn't add any direct value to your omelet, it makes getting the eggs home from the store so easy that you wouldn't think about transporting eggs any other way.

Each egg in your EAR carton is a specific piece of the J2EE puzzle. These eggs (or JARs) come in three basic varieties called "modules":

Web module

A WAR file containing presentation tier components

EJB module

An EJB JAR file containing the middle-tier components (EJBs, MDBs, etc.)

Java module

A regular JAR file containing classes and libraries that are shared across the entire application. An application client JAR and a common JAR are two examples of Java modules.

An EAR can contain at least one of any of these modules. By the same token, any of them can be safely omitted if they aren't needed. Figure 3-1 shows the structure of an EAR file.

Figure 3-1. EAR file structure