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 Using Plugin Tools Java5 Annotations
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 Olivier Lamy
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 2012-05-14
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~~ "License"); you may not use this file except in compliance
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~~
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Using Plugin Tools Java Annotations

 Since version 3.0 of the maven-plugin-plugin, you can use Java5 annotations to generate the 
 plugin descriptor file.

 <<NOTE>> With annotations, your Mojo super class does not any more require to be in the same project. Provided that the super class also uses annotations, it
 can now come from reactor projects or external dependencies. By default all dependencies are scanned, but this can be reduced with the <<<mojoDependencies>>>
 parameter. As javadoc doclet are still useful for <<<@since>>>, <<<@deprecated>>> and comments, the sources are still scanned. So if you use an external 
 dependency, you must still provide an artifact with sources (<<<sources>>> classifier) to provide documentation (the tooling will skip error if this artifact 
 sources is missing).

* Annotations

  Information for plugin descriptor generation is specified using 4 annotations:

  * 2 class-level annotations:

    * <<<@Mojo>>>: This annotation will mark your class as a Mojo,

    * <<<@Execute>>>: Used if your Mojo needs to fork a lifecycle,

    []

  * 2 field-level annotations:

    * <<<@Parameter>>>: Used to configure your Mojo parameters,

    * <<<@Component>>>: Used to configure injection of Plexus components or Maven context components.

    []

  []

  For more information on these annotations, see the
  {{{../../maven-plugin-tools-annotations/index.html#Supported_Annotations}corresponding documentation}}.

  Notice that Plugin Tools Java Annotations are named after Plugin Tools Javadoc Tags
  with following little differences:

*-------------------------------+---------------+
|| {{{../../maven-plugin-tools-java/index.html}Plugin Tools Javadoc Tags}} || {{{../../maven-plugin-tools-annotations/index.html}Plugin Tools Java Annotation}} ||
*-------------------------------+---------------+
| <<<@goal "goal-name">>>       | <<<@Mojo( name = "goal-name" )>>>
*-------------------------------+---------------+
| <<<@phase "\<phase-name\>">>> | <<<@Mojo( defaultPhase = LifecyclePhase.\<phase\> )>>>
*-------------------------------+---------------+

* POM configuration

  To be able to use these Java annotations, you need to add some configuration to your plugin POM:

  * add <<<maven-plugin-annotations>>> dependency, preferably with <<<provided>>> scope,

  * override Maven core's <<<default-descriptor>>> execution phase to <<<process-classes>>>,

  []

+-----+
<project>
  ...
  <packaging>maven-plugin</packaging>
  ...
  <dependencies>
    <!-- dependencies to annotations -->
    <dependency>
      <groupId>org.apache.maven.plugin-tools</groupId>
      <artifactId>maven-plugin-annotations</artifactId>
      <version>${project.version}</version>
      <optional>true</optional> <!-- annotations are not used at runtime because @Retention(value=CLASS), they are needed only to build the plugin -->
    </dependency>
  </dependencies>
  ...
  <build>
    <plugins>
      <plugin>
        <groupId>org.apache.maven.plugins</groupId>
        <artifactId>maven-plugin-plugin</artifactId>
        <version>${project.version}</version>
        <executions>
          <execution>
            <id>default-descriptor</id>
            <phase>process-classes</phase>
          </execution>
          <!-- if you want to generate help goal -->
          <execution>
            <id>help-goal</id>
            <goals>
              <goal>helpmojo</goal>
            </goals>
          </execution>
        </executions>
      </plugin>
    </plugins>
  ...
  </build>
  ...
</project>
+-----+

 <Notice>: this configuration will not work with Maven 2, which does not support execution phase overriding.
 If you absolutely need to build with Maven 2, you should use <<<skipErrorNoDescriptorsFound>>> parameter
 to avoid failure on default execution phase and add another execution:
 
+-----+
<project>
  ...
  <profiles>
    <profile>
      <id>maven-2</id>
      <activation>
        <file>
          <!--  This employs that the basedir expression is only recognized by Maven 3.x (see MNG-2363) -->
          <missing>${basedir}</missing>
        </file>
      </activation>
      <build>
        <plugins>
          <plugin>
            <groupId>org.apache.maven.plugins</groupId>
            <artifactId>maven-plugin-plugin</artifactId>
            <configuration>
              <!-- see https://issues.apache.org/jira/browse/MNG-5346 -->
              <skipErrorNoDescriptorsFound>true</skipErrorNoDescriptorsFound>
            </configuration>
            <executions>
              <execution>
                <id>mojo-descriptor</id>
                <goals>
                  <goal>descriptor</goal>
                </goals>
              </execution>
            </executions>
          </plugin>
        </plugins>
      </build>
    </profile>    
  </profiles>
</project>
+-----+