[Maven] Configuring libs for WARs inside EARs

[Ryan Kade]

I'm migrating our build process from Ant 1.7.0 to Maven 2.0.6, and I've got a whole series of JARs that I've written POMs for, most of which reside inside one of two WARs, which in turn live inside a single EAR.

Some of the projects inside the two WARs share libraries, and so I don't want to have those libraries duplicated in the WAR WEB-INF/lib directories, but rather include them in the EAR and make a reference to them in the WAR manifest. Maven doesn't support this directly, but they do have a workaround as described here:

Creating Skinny WARs

I don't like this solution, since it requires me to specify by name the libraries I want to exclude (using the warSourceExcludes parameter of the maven-war-plugin), which sort of breaks Maven's flexibility, no? Now I have to specify filenames that I'd rather have Maven construct based on my groupId-artifactId-version.

So I concocted an alternative solution. All my POMs for this particular project (JARs, WARs, EAR) inherit from one "master" POM (not the Super POM). I have a huge DependencyManagement section which specifies all the libraries any of the sub-projects would need, along with preferred versions.

When I run across a library that I need to be in the EAR and not in a WAR's WEB-INF/lib, I set it's scope to "provided" in the master POM. Then, in the Dependency section of the EAR, I override it to "compile." For example:

Master POM
 
<project>
  ...
  <dependencyManagement>
    <dependencies>
      <dependency>
<groupId>commons-digester</groupId>
<artifactId>commons-digester</artifactId>
<version>1.6</version>
        <scope>provided</scope>
      </dependency>
    </dependencies>
  </dependencyManagement>
  ...
</project>
 
POM for EAR
 
<project>
  ...
  <dependencies>
    <dependency>
      <groupId>commons-digester</groupId>
      <artifactId>commons-digester</artifactId>
      <scope>compile</scope>
    </dependency>
  </dependencies>
  ...
</project>
 
POM for WAR
 

<project>
  ...
  <dependencies>
    <dependency>
      <groupId>commons-digester</groupId>
      <artifactId>commons-digester</artifactId>
    </dependency>
  </dependencies>
  ...
</project>
 

I still have to add the libraries to the manifest--no getting out of that--but then I don't have to specifically exclude them.

In this way, my WAR has no problem compiling, but still looks to the EAR for those joint dependencies.

My question: is this a bad way to do this? Am I hijacking the purpose of the "provided" scope and potentially introducing problems for myself down the road?

What do y'all think?

[Ryan Kade]

After further research, I decided to do this in the reverse. Rather than setting the scope of all the libraries needed by my WARs (yet located in the EAR) to "provided" in the master POM, I do it in each individual WAR file. This functions as an effective exclusion (for transitive dependencies), while still allowing the dependency to be declared in both the WAR and the EAR.

This strikes me as more consistent with the use of the provided scope.

Example:

    
 
Master POM
 
<project>
  ...
  <dependencyManagement>
    <dependencies>
      <dependency>
<groupId>commons-digester</groupId>
<artifactId>commons-digester</artifactId>
<version>1.6</version>
      </dependency>
    </dependencies>
  </dependencyManagement>
  ...
</project>
 
POM for EAR
 
<project>
  ...
  <dependencies>
    <dependency>
      <groupId>commons-digester</groupId>
      <artifactId>commons-digester</artifactId>
    </dependency>
  </dependencies>
  ...
</project>
 
POM for WAR
 
 
<project>
  ...
  <dependencies>
    <dependency>
      <groupId>commons-digester</groupId>
      <artifactId>commons-digester</artifactId>
        <scope>provided</scope>
    </dependency>
  </dependencies>
  ...
</project>

[ June 27, 2007: Message edited by: Ryan Kade ]
[ June 27, 2007: Message edited by: Ryan Kade ]