public  void execute(MavenSession session,
    ReactorManager rm,
    EventDispatcher dispatcher) throws LifecycleExecutionException, BuildFailureException 
{
        // TODO: This is dangerous, particularly when it's just a collection of loose-leaf projects being built
        // within the same reactor (using an inclusion pattern to gather them up)...
        MavenProject rootProject = rm.getTopLevelProject();
        List goals = session.getGoals();
        if ( goals.isEmpty() && rootProject != null )
        {
            String goal = rootProject.getDefaultGoal();
            if ( goal != null )
            {
                goals = Collections.singletonList( goal );
            }
        }
        if ( goals.isEmpty() )
        {
            throw new BuildFailureException( "\n\nYou must specify at least one goal. Try 'mvn install' to build or 'mvn -?' for options \nSee http://maven.apache.org for more information.\n\n" );
        }
        List taskSegments = segmentTaskListByAggregationNeeds( goals, session, rootProject );
        // TODO: probably don't want to do all this up front
        findExtensions( session );
        executeTaskSegments( taskSegments, rm, session, rootProject, dispatcher );
}

Execute a task. Each task may be a phase in the lifecycle or the execution of a mojo.

 public Map getPhaseToLifecycleMap() throws LifecycleExecutionException 
{
        if ( phaseToLifecycleMap == null )
        {
            phaseToLifecycleMap = new HashMap();
            for ( Iterator i = lifecycles.iterator(); i.hasNext(); )
            {
                Lifecycle lifecycle = (Lifecycle) i.next();
                for ( Iterator p = lifecycle.getPhases().iterator(); p.hasNext(); )
                {
                    String phase = (String) p.next();
                    if ( phaseToLifecycleMap.containsKey( phase ) )
                    {
                        Lifecycle prevLifecycle = (Lifecycle) phaseToLifecycleMap.get( phase );
                        throw new LifecycleExecutionException( "Phase '" + phase +
                            "' is defined in more than one lifecycle: '" + lifecycle.getId() + "' and '" +
                            prevLifecycle.getId() + "'" );
                    }
                    else
                    {
                        phaseToLifecycleMap.put( phase, lifecycle );
                    }
                }
            }
        }
        return phaseToLifecycleMap;
}

 protected  void line() 
{
        getLogger().info( "------------------------------------------------------------------------" );
}