break;

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

                case ProjectSkipped:
                    listener.projectSkipped(event);
                    break;
                case ProjectStarted:

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

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

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

 *
 */
public interface ExecutionListener {

    void projectDiscoveryStarted(ExecutionEvent event);

    void sessionStarted(ExecutionEvent event);

    void sessionEnded(ExecutionEvent event);

    void projectSkipped(ExecutionEvent event);

    void projectStarted(ExecutionEvent event);

    void projectSucceeded(ExecutionEvent event);

    public void onEvent(Object event) {
        if (event instanceof ExecutionEvent) {
            ExecutionEvent executionEvent = (ExecutionEvent) event;
            if (executionEvent.getType() == ExecutionEvent.Type.SessionEnded) {
                allHandlers.clear();
            }
        }
    }

    @Override
    public ArtifactHandler getArtifactHandler(String id) {
        return allHandlers.computeIfAbsent(id, k -> {

        // default does nothing
    }

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

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

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

    public void onEvent(Object event) {
        if (event instanceof ExecutionEvent) {
            ExecutionEvent executionEvent = (ExecutionEvent) event;
            if (executionEvent.getType() == ExecutionEvent.Type.SessionEnded) {
                allHandlers.clear();
            }
        }
    }

    public ArtifactHandler getArtifactHandler(String type) {
        requireNonNull(type, "null type");

 *
 */
public interface ExecutionEvent {

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

        } catch (Exception e) {
            result.addException(e);
        } finally {
            eventCatapult.fire(ExecutionEvent.Type.SessionEnded, session, null);
        }
    }

    private boolean buildExecutionRequiresProject(MavenSession session) {
        return lifecycleTaskSegmentCalculator.requiresProject(session);
    }

    public void onEvent(Object event) {
        if (event instanceof ExecutionEvent) {
            ExecutionEvent executionEvent = (ExecutionEvent) event;
            if (executionEvent.getType() == ExecutionEvent.Type.SessionEnded) {
                usedTypes.clear();
            }
        }
    }

    @Override
    public Optional<Type> lookup(String id) {
        return Optional.of(require(id));
    }

    @Override

                validationPluginExcludes(repositorySystemSession);
            } else if (executionEvent.getType() == ExecutionEvent.Type.SessionEnded) {
                reportSessionCollectedValidationIssues(executionEvent.getSession());
            }
        }
    }

    private List<?> validationPluginExcludes(RepositorySystemSession session) {