log4j configuration file in a multi-module Maven project

Question

I am working on a multi-module Maven project, whose structure is like this:

war-module
jar-module

The war-module depends on the jar-module,

Answer 1

From my experience this can be implemented in an easy way , just :

1. Make the log4j configuration resource at the parent module.
2. Call the dependency of log4j in all pom modules.

Detailed steps:

1. Create a project with common-config
2. In the src/main/resources folder put the log4j or logback config file
3. Install the artifact in the local Maven repository to be used by other projects
4. Add the dependency as a normal Maven dependency in the subsequent projects

<dependency> 
  <groupId>com.your.group.id</groupId> 
  <artifactId>common-config</artifactId> 
  <scope>provided</scope> 
</dependency>

I prefer to use the scope provided and provide the file from a classpath config folder at runtime.

Answer 2

I found the answer via some more searching on the web.

Generally, there are three ways to share resources in a multi module Maven project:

• Cut and paste them.
• Use Assembly and Dependency plugins
• Use the maven-remote-resources-plugin

Here's a blog post from Sonatype, the company behind Maven, on sharing resources across projects in Maven, and it is the exact answer I need:

http://www.sonatype.com/people/2008/04/how-to-share-resources-across-projects-in-maven/

Answer 3

In the jar module, exclude the file from the jar:

<plugin>
    <groupId>org.apache.maven.plugins</groupId>
    <artifactId>maven-jar-plugin</artifactId>
    <version>2.3.1</version>
    <configuration>
      <excludes>
        <exclude>log4j.xml</exclude>
      </excludes>
    </configuration>
</plugin>

Use the buildhelper plugin to attach the log4j.xml to the build as a separate artifact

<plugin>
    <groupId>org.codehaus.mojo</groupId>
    <artifactId>build-helper-maven-plugin</artifactId>
    <version>1.5</version>
    <executions>
      <execution>
        <id>attach-artifacts</id>
        <phase>package</phase>
        <goals>
          <goal>attach-artifact</goal>
        </goals>
        <configuration>
          <artifacts>
            <artifact>
              <file>${project.build.outputDirectory}/log4j.xml</file>
              <type>xml</type>
              <classifier>log4j</classifier>
            </artifact>
          </artifacts>
        </configuration>
      </execution>
    </executions>
</plugin>

Now in your war artifact, copy the xml to the output directory:

<plugin>
    <groupId>org.apache.maven.plugins</groupId>
    <artifactId>maven-dependency-plugin</artifactId>
    <executions>
      <execution>
        <id>copy</id>
        <phase>prepare-package</phase>
        <goals>
          <goal>copy</goal>
        </goals>
        <configuration>
          <artifactItems>
            <artifactItem>
              <groupId>${project.groupId}</groupId>
              <artifactId>your.jar.project.artifactId</artifactId>
              <version>${project.version}</version>
              <type>xml</type>
              <classifier>log4j</classifier>
              <outputDirectory>${project.build.outputDirectory}
              </outputDirectory>
              <destFileName>log4j.xml</destFileName>
            </artifactItem>
          </artifactItems>
        </configuration>
      </execution>
    </executions>
</plugin>

But of course it would be easier to just put the file in [web-artifact]/src/main/resources in the first place :-)