Use maven 3 apis in a hudson plugin

Using maven 3 apis in a hudson needs to change classLoader hierarchy as hudson load some old maven artifacts in the parent classLoader.
So the solution is to use a child first classLoader.
This new classLoader has been introduced in hudson 1.378. (see HUDSON-5360).
So you can now use it to made your plugin dependencies win on hudson core classLoader.
Some steps are needed.
Configuring your hpi plugin

  <plugin>
    <groupid>org.jvnet.hudson.tools</groupid>
    <artifactid>maven-hpi-plugin</artifactid>
    <version>1.54</version>
    <configuration>
      <pluginFirstClassLoader>true</pluginFirstClassLoader>
    </configuration>         
  </plugin>

So now your pluginWrapper.classLoader will be of type PluginFirstClassLoader.

// pluginId is project.artifactId from your plugin pom
PluginWrapper pluginWrapper = Hudson.getInstance().getPluginManager().getPlugin( pluginId );
PluginFirstClassLoader pluginFirstClassLoader = (PluginFirstClassLoader) pluginWrapper.classLoader;

Now everthing is ready but some other tricks are needed :-)

Create a PlexusContainer (note you must use the new "plexus-guice" bridge).
This means you need the following dependency :

<dependency>
  <groupId>org.sonatype.sisu</groupId>
  <artifactId>sisu-inject-plexus</artifactId>
  <version>1.4.1</version>
</dependency>

And very important you must exclude dependencies from the original plexus-container

    <dependency>
      <groupId>org.sonatype.aether</groupId>
      <artifactId>aether-connector-wagon</artifactId>
      <version>${aetherVersion}</version>
      <exclusions>
        <exclusion>
          <groupId>org.codehaus.plexus</groupId>
          <artifactId>plexus-container-default</artifactId>
        </exclusion>
      </exclusions>      
    </dependency>  

To prevent this you can add an enforcer rule which will chech plexus-container-default inclusion

      <plugin>
        <groupId>org.apache.maven.plugins</groupId>
        <artifactId>maven-enforcer-plugin</artifactId>
        <version>1.0-beta-1</version>
        <executions>
          <execution>
            <goals>
              <goal>enforce</goal>
            </goals>
            <phase>validate</phase>
            <id>ensure-no-plexus-container</id>
            <configuration>
              <rules>
                <bannedDependencies>
                  <excludes>
                    <exclude>org.codehaus.plexus:plexus-container-default</exclude>
                  </excludes>
                  <message>
                  ensure-no-plexus-container doesn't work anymore with maven 3 librairies. you have to add some exclusions.
                  </message>
                </bannedDependencies>
              </rules>
              <fail>true</fail>
            </configuration>
          </execution>
        </executions>
      </plugin>

How to create the PlexusContainer from the PluginFirstClassLoader :

    private PlexusContainer getPlexusContainer(PluginFirstClassLoader pluginFirstClassLoader) throws PlexusContainerException {
        DefaultContainerConfiguration conf = new DefaultContainerConfiguration();
        ClassWorld world = new ClassWorld();
        ClassRealm classRealm = new ClassRealm( world, "project-building", pluginFirstClassLoader );
        // olamy yup hackish but it's needed for plexus-shim which needs a URLClassLoader and PluginFirstClassLoader is not
        for ( URL url : pluginFirstClassLoader.getURLs() )
        {
            classRealm.addURL( url );
            LOGGER.fine(  "add url " + url.toExternalForm() );
        }
        conf.setRealm( classRealm );

        return new DefaultPlexusContainer( conf );
    }

Then set the current Thread classLoader (don't miss to restore the original one in a finally statement

PlexusContainer plexusContainer = getPlexusContainer( pluginFirstClassLoader );

Thread.currentThread().setContextClassLoader( plexusContainer.getContainerRealm() );

Now you can play with maven 3 apis

ProjectBuilder projectBuilder = plexusContainer.lookup( ProjectBuilder.class );

A first sample is the plugin called : maven-dependency-update-trigger
: sources and Wiki Page (under construction :-) )
You must have a look at the dependencies used.

The plugin will check your project according to a cron expression and schedule a build if a snapshot dependency has changed (dependency and plugin).

It will be released as son as hudson 1.378 will be released.

Note : hpi:run doesn't work yet for this plugin as it needs some changes in the hpi mojo to handle the new PluginFirstClassLoader.