my first m2 plugin

[Torsten Curdt]

Ok, guys

I am trying to get started with writing my first m2 plugin.
But I've run into some problems. (using maven 2.0.1)

I've created a simple mojo:

 /**
  * @goal minijar
  * @description strips unused classes from the dependencies
  * @resolveTransitiveDependencies
  * */
 public final class MiniJarMojo extends AbstractMojo {

    /**
     * @parameter expression="${project.artifacts}"
     * */
    private Set dependencies;

    /**
     * @parameter expression="${project.runtimeClasspathElements}"
     * */
    private Set runtimeClazzpath;

    private File directory;

    public void setOutputDirectory( final String pDirectory ) {
        directory = new File(pDirectory);
    }

    public void execute() throws MojoExecutionException {

        System.out.println("dependencies: " + dependencies);
        System.out.println("classpath: " + runtimeClazzpath);

    }
 }

With the following pom.xml

 <project>
  <parent>
    <artifactId>maven-plugin-parent</artifactId>
    <groupId>org.apache.maven.plugins</groupId>
    <version>2.0</version>
  </parent>
  <modelVersion>4.0.0</modelVersion>
  <groupId>minijar.plugin</groupId>
  <artifactId>maven-minijar-plugin</artifactId>
  <packaging>maven-plugin</packaging>
  <name>Maven MiniJar Plugin</name>
  <version>1.0-SNAPSHOT</version>
  <dependencies>
    <dependency>
      <groupId>org.apache.maven</groupId>
      <artifactId>maven-project</artifactId>
    </dependency>
  </dependencies>
 </project>

A "mvn install" works just fine. Then I integrated
the plugin into my project's pom.xml

  <build>
    <sourceDirectory>src/java</sourceDirectory>
    <pluginManagement>
      <plugins>
        <plugin>
          <groupId>minijar.plugin</groupId>
          <artifactId>maven-minijar-plugin</artifactId>
          <configuration></configuration>
        </plugin>
      </plugins>
    </pluginManagement>
  </build>

Now when I call "mvn minijar:minijar" I get the following error...

[INFO] Searching repository for plugin with prefix: 'minijar'.

[ERROR] FATAL ERROR

[INFO] null

[INFO] Trace
java.lang.NullPointerException


Am I missing something obvious here?
Any idea?

cheers
--
Torsten

[INFO] ------------------------------------------------------------------------ ---- [INFO] ------------------------------------------------------------------------ ---- [INFO] ------------------------------------------------------------------------ ---- at org.apache.maven.plugin.descriptor.PluginDescriptor.getMojo (PluginDescriptor.java:259) at org.apache.maven.lifecycle.DefaultLifecycleExecutor.getMojoDescriptor (DefaultLifecycleExecutor.java:1443) at org.apache.maven.lifecycle.DefaultLifecycleExecutor.segmentTaskListByAgg regationNeeds(DefaultLifecycleExecutor.java:378) at org.apache.maven.lifecycle.DefaultLifecycleExecutor.execute (DefaultLifecycleExecutor.java:134)

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