How to generate jar for maven parent project

Question

Maven requires a parent project to have

<packaging>pom</packaging>

clause in the parent's pom.xml. When such a project installed, only a pom-file generated into the maven repository. Jar-file is not generated, no matter if the parent project has any Java code. That forces me to have extra empty parent projects, which is overkill. Logically, some of my libraries could be parents at the same time.

Is there a way to generate both pom and jar files for a parent project without removing/adding the packaging clause between installs?

Answer 1

Use Maven Jar Plugin and Maven Build Helper. Example POM:

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
  <modelVersion>4.0.0</modelVersion>

  <groupId>test</groupId>
  <artifactId>test</artifactId>
  <version>1.0</version>

  <packaging>pom</packaging>

  <build>
    <plugins>
      <plugin>
        <groupId>org.codehaus.mojo</groupId>
        <artifactId>build-helper-maven-plugin</artifactId>
        <version>1.7</version>
        <executions>
          <execution>
            <id>attach-artifacts</id>
            <phase>package</phase>
            <goals>
              <goal>attach-artifact</goal>
            </goals>
            <configuration>
              <artifacts>
                <artifact>
                  <file>test-${project.version}</file>
                  <type>jar</type>
                </artifact>
              </artifacts>
            </configuration>
          </execution>
        </executions>
      </plugin>
      <plugin>
        <groupId>org.apache.maven.plugins</groupId>
        <artifactId>maven-jar-plugin</artifactId>
        <version>2.4</version>
        <executions>
          <execution>
            <id>default</id>
            <goals>
              <goal>jar</goal>
            </goals>
            <phase>package</phase>
          </execution>
        </executions>
      </plugin>
    </plugins>
  </build>
</project>

Maven build results:

mvn install
[INFO] Scanning for projects...
[INFO]                                                                         
[INFO] ------------------------------------------------------------------------
[INFO] Building test 1.0
[INFO] ------------------------------------------------------------------------
[INFO] 
[INFO] --- build-helper-maven-plugin:1.7:attach-artifact (attach-artifacts) @ test ---
[INFO] 
[INFO] --- maven-jar-plugin:2.4:jar (default) @ test ---
[WARNING] JAR will be empty - no content was marked for inclusion!
[INFO] 
[INFO] --- maven-install-plugin:2.3.1:install (default-install) @ test ---
[INFO] Installing /home/username/projects/test/pom.xml to /home/username/.m2/repository/test/test/1.0/test-1.0.pom
[INFO] Installing /home/username/projects/test/test-1.0 to /home/username/.m2/repository/test/test/1.0/test-1.0.jar
[INFO] ------------------------------------------------------------------------
[INFO] BUILD SUCCESS
[INFO] ------------------------------------------------------------------------
[INFO] Total time: 0.805s
[INFO] Finished at: Thu Sep 06 13:33:20 EDT 2012
[INFO] Final Memory: 4M/119M
[INFO] ------------------------------------------------------------------------

A note on Maven practices:

Parent modules are typically where you define the dependencies and plugins used in common by all your child modules. It rarely has output of its own. You probably want to have a "distribution" sub-module that aggregates all your other module artifacts, rather than attempting to do it in the parent module.