switch (eventType) {
                case ProjectDiscoveryStarted:
                    listener.projectDiscoveryStarted(event);
                    break;

                case SessionStarted:
                    listener.sessionStarted(event);
                    break;
                case SessionEnded:
                    listener.sessionEnded(event);
                    break;

                case ProjectSkipped:

 * {@link AbstractExecutionListener} in order to avoid interoperability problems.
 *
 */
public interface ExecutionListener {

    void projectDiscoveryStarted(ExecutionEvent event);

    void sessionStarted(ExecutionEvent event);

    void sessionEnded(ExecutionEvent event);

    void projectSkipped(ExecutionEvent event);

    void projectStarted(ExecutionEvent event);

        dispatcher.onEvent(event);
        delegate.projectDiscoveryStarted(event);
    }

    @Override
    public void sessionStarted(ExecutionEvent event) {
        dispatcher.onEvent(event);
        delegate.sessionStarted(event);
    }

    @Override
    public void sessionEnded(ExecutionEvent event) {
        dispatcher.onEvent(event);
        delegate.sessionEnded(event);
    }

 *
 */
public class AbstractExecutionListener implements ExecutionListener {

    public void projectDiscoveryStarted(ExecutionEvent event) {
        // default does nothing
    }

    public void sessionStarted(ExecutionEvent event) {
        // default does nothing
    }

    public void sessionEnded(ExecutionEvent event) {
        // default does nothing
    }

    public void projectSkipped(ExecutionEvent event) {

 *
 */
public interface ExecutionEvent {

    /**
     * The possible types of execution events.
     */
    enum Type {
        ProjectDiscoveryStarted,
        SessionStarted,
        SessionEnded,
        ProjectSkipped,
        ProjectStarted,
        ProjectSucceeded,
        ProjectFailed,
        MojoSkipped,
        MojoStarted,
        MojoSucceeded,
        MojoFailed,

        this.builders = builders;
    }

    @Override
    public void execute(MavenSession session) {
        eventCatapult.fire(ExecutionEvent.Type.SessionStarted, session, null);

        ReactorContext reactorContext = null;
        ProjectBuildList projectBuilds = null;
        MavenExecutionResult result = session.getResult();

        try {

    public void onEvent(Object event) {
        if (event instanceof ExecutionEvent) {
            ExecutionEvent executionEvent = (ExecutionEvent) event;
            if (executionEvent.getType() == ExecutionEvent.Type.SessionStarted) {
                RepositorySystemSession repositorySystemSession =
                        executionEvent.getSession().getRepositorySession();