Creating Skinny WARs

In a typical J2EE environment, a WAR is packaged within an EAR for deployment. The WAR can contain all its dependent JARs in WEB-INF/lib but then the EAR can quickly grow very large if there are multiple WARs, due to the presence of duplicate JARs. Instead the J2EE specification allows WARs to reference external JARs packaged within the EAR via the Class-Path setting in their MANIFEST.MF.

The Maven EAR Plugin has direct support for creating skinny wars which simply means to configure the maven-ear-plugin accordingly.

You need to change the EAR project's pom.xml to package those dependent JARs in the EAR. Notice that we package everything into a lib/ directory within the EAR. This is just my own personal preference to distinguish between J2EE modules (which will be packaged in the root of the EAR) and Java libraries (which are packaged in lib/).

<project>
  ...
  <build>
    <plugins>
      <plugin>
        <artifactId>maven-ear-plugin</artifactId>
        <version>2.9.1</version>
        <configuration>
          <defaultLibBundleDir>lib/</defaultLibBundleDir>
          <skinnyWars>true</skinnyWars>
        </configuration>
      </plugin>
    </plugins>
  </build>
  ...
</project>

Now the painful part. Your EAR project's pom.xml needs to list every dependency that the WAR has. This is because Maven assumes fat WARs and does not include transitive dependencies of WARs within the EAR.

<project>
  ....
  <dependencies>
    <dependency>
      <groupId>com.acme</groupId>
      <artifactId>shared-jar</artifactId>
      <version>1.0.0</version>
    </dependency>
    <dependency>
      <groupId>com.acme</groupId>
      <artifactId>war1</artifactId>
      <version>1.0.0</version>
      <type>war</type>
    </dependency>
    <dependency>
      <groupId>com.acme</groupId>
      <artifactId>war2</artifactId>
      <version>1.0.0</version>
      <type>war</type>
    </dependency>
  </dependencies>
  ...
</project>

Your EAR will contain something like this:

 .
 |-- META-INF
 |   `-- application.xml
 |-- lib
 |   `-- shared-jar-1.0.0.jar
 |-- war1-1.0.0.war
 `-- war2-1.0.0.war