Re: Detecting whether or not the user changed anything on a form

[Andrew Robinson]

I think this will do unless you can think of a way to avoid having to add the 
VCL tag to every component.

This is when you may consider a PhaseListener, or component binding.
You could surf the entire component tree recursively, and add your VCL
to all components implementing EditableValueHolder.

public class VCLPhaseListener implement PhaseListener {
 public void afterPhase(PhaseEvent event) { }

        public void beforePhase(PhaseEvent event) {
   UIViewRoot viewRoot = event.getFacesContext().getViewRoot();
   if (viewRoot != null) {
     addVCL(viewRoot);
   }
 }

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

 private void addVCL(UIComponent component) {
   if (component instanceof EditableValueHolder &&
     !hasVCL((EditableValueHolder)component)) {
     ((EditableValueHolder)component).addValueChangeListener(this);
   }
   for (Iterator iter = component.getFacetsAndChildren(); iter.hasNext(); ) {
     addVCL(iter.next());
   }
 }

 private boolean hasVCL(EditableValueHolder holder) {
   for (ValueChangeListener listener : holder.getValueChangeListeners()) {
     if (VCLPhaseListener.class.assignableFrom(listener.getClass())) {
       return true;
     }
   }
   return false;
 }

 ... VCL Code
}