How to trace a running JSF life cycle phases?

You can use a PhaseListener to trace the phases of the JSF lifecycle and execute some processes where required. But you can also use a "dummy" PhaseListener to debug the phases to see what is happening in which phase. Here is a basic example of such a LifeCycleListener:

Note: if you don't have a JSF playground environment setup yet, then you may find this tutorial useful as well: JSF tutorial with Eclipse and Tomcat.

package mypackage;

import javax.faces.event.PhaseEvent;
import javax.faces.event.PhaseId;
import javax.faces.event.PhaseListener;

public class LifeCycleListener implements PhaseListener {

    public PhaseId getPhaseId() {
        return PhaseId.ANY_PHASE;
    }

    public void beforePhase(PhaseEvent event) {
        System.out.println("START PHASE " + event.getPhaseId());
    }

    public void afterPhase(PhaseEvent event) {
        System.out.println("END PHASE " + event.getPhaseId());
    }

}

Add the following lines to the faces-config.xml to activate the LifeCycleListener.

<lifecycle>
    <phase-listener>mypackage.LifeCycleListener</phase-listener>
</lifecycle>

This produces like the following in the system output:

START PHASE RESTORE_VIEW 1
END PHASE RESTORE_VIEW 1
START PHASE APPLY_REQUEST_VALUES 2
END PHASE APPLY_REQUEST_VALUES 2
START PHASE PROCESS_VALIDATIONS 3
END PHASE PROCESS_VALIDATIONS 3
START PHASE UPDATE_MODEL_VALUES 4
END PHASE UPDATE_MODEL_VALUES 4
START PHASE INVOKE_APPLICATION 5
END PHASE INVOKE_APPLICATION 5
START PHASE RENDER_RESPONSE 6