Unable to disable generation of empty JAR (maven-jar-plugin) - maven

Question

Sometimes, my Talend Open Studio components have resources but not Java sources (they are purely metadata components). I need to disable the generation of JAR files in such a case.
I configured the maven-jar-plugin this way:
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-jar-plugin</artifactId>
<version>2.4</version>
<configuration>
<forceCreation>false</forceCreation>
<skipIfEmpty>true</skipIfEmpty>
<useDefaultManifestFile>false</useDefaultManifestFile>
</configuration>
</plugin>
but I still get the ${project.name}.jar file with pom.properties, pom.cml, the manifest and an empty file App.class containing only "class {}"
While I can disable the includes of all maven stuff using this:
<archive>
<addMavenDescriptor>false</addMavenDescriptor>
</archive>
I still get a JAR with the manifest file inside it
Are there some configuration parameters I misconfigured?

Answer 1

Most efficient way to disable the creation of jars is to configure the maven-jar-plugin like this:
<plugins>
<plugin>
<artifactId>maven-jar-plugin</artifactId>
<version>2.3.1</version>
<executions>
<execution>
<id>default-jar</id>
<phase>none</phase>
</execution>
</executions>
</plugin>
</plugins>
It will place the default jar creation in the none phase, it will never be run.

Answer 2

I found the solution by myself, even if it's only a workaround. I delete the JAR using a delete antrun task if /src/main/java directory doesn't exist:
<!-- remove the empty JAR if not needed -->
<if>
<not><available file="${basedir}/src/main/java" type="dir" /></not>
<then>
<delete file="${project.build.directory}/${project.name}-${project.version}.jar"/>
</then>
</if>
this task requires antcontrib to work properly and, ofc, it doesn't work if you plan to do releases with maven (but it's ok for metadata-only components, like Talend Open Studio plugins)

Answer 3

You can instruct maven-jar-plugin to not generate META-INF/maven/*/pom. files, as explained in Maven Archiver Reference.
Also, you can use its skipIfEmpty option.
Following code combines both these (just to have them copy-paste ready):
...
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-jar-plugin</artifactId>
<version>2.4</version>
<configuration>
<skipIfEmpty>true</skipIfEmpty>
<archive>
<addMavenDescriptor>false</addMavenDescriptor>
</archive>
...
This works fine, but when you do mvn install, it fails due to missing project artifact.
Similar problem will probably be with mvn deploy and with release, but I didn't check these.
However, if you can live with antrun's delete, the property skipIfEmpty will probably work well for you, and is a bit more elegant. At least it does not introduce a new execution and its dependencies etc.