Generic Way to Catch Backing Bean Exceptions Possible ?

Question

For customizing the way errors are shown to the user I already have:
- Override the method reportErrors(PageLifecycleContext) as described in the section "20.8.1 How to Change Exception Handling"
- Created a custom subclass of DCJboDataControl (as example#55 on Steve blog) and override the beginRequest() for exceptions like a JDBC connection error.
However I have one more situation I would like to have a generic solution and that is for the backing action methods that can throw exceptions not being handled by a try {} catch {} statement. Ex: NullPointerException. Currently what happens in that case is that a 500 Internal Server Error page is shown to the user.
I was thinking of having a servlet filter, but I am not sure if that is the best way to achieve it.
Any thought is welcomed.
Thanks,
Claudio.

Answer 1

Sure, but I warn you, that example won't be portable directly from a JSF implementation to another (RI vs. MyFaces mainly) as you have to use directly an implementation class. It's really a minor change from one implementation to another though.
There's a portable way, but it implies rewriting the full Lifecycle class on your own (which I did to add new features as well, but you should do that until you're fully comfortable with the specification). Anyway, here's the simple example
In faces-config.xml
<factory>
  <lifecycle-factory>mypackage.MyLifecycleFactory</lifecycle-factory>
</factory>In MyLifecycleFactory class
public class MyLifecycleFactory extends LifecycleFactoryImpl
  private Map<String, Lifecycle> cache;
  public MyLifecycleFactory()
    cache = new HashMap<String, Lifecycle>(3);
  public Lifecycle getLifecycle(String lifecycleId)
    Lifecycle lifecycle = cache.get(lifecycleId);
    if (lifecycle == null)
      lifecycle = super.getLifecycle();
      if (lifecycle == null)
        return null;
      lifecycle = new LifecycleDecorator(lifecycle);
      cache.put(lifecycleId, lifecycle);
    return lifecycle;
}Where LifecycleFactoryImpl is com.sun.faces.lifecycle.LifecycleFactoryImpl in JSF RI and org.apache.myfaces.lifecycle.LifecycleFactoryImpl in MyFaces (that's the only change you have to do for it to work in an implementation or another).
In LifecycleDecorator class
public class LifecycleDecorator extends Lifecycle
  private Lifecycle wrapped;
  public LifecycleDecorator(Lifecycle wrapped)
    this.wrapped = wrapped;
  public void execute(FacesContext context)
    try
      wrapped.execute(context);
    catch (Exception e)
      // Do something
  public void render(FacesContext context)
    try
      wrapped.render(context);
    catch (Exception e)
      // Do something
  public void addPhaseListener(PhaseListener listener)
    wrapped.addPhaseListener(listener);
  public void removePhaseListener(PhaseListener listener)
    wrapped.removePhaseListener(listener);
  public PhaseListener[] getPhaseListeners()
    return wrapped.getPhaseListeners();
}Regards,
~ Simon