public IFilter getFilterFor(final Class<? extends PersistentObject> clazz) {
   IObjectFilterProvider prov = hash.get(clazz);
   if (prov != null) {
     return prov.getFilter();
   }
   return null;
 }
 public synchronized void registerObjectFilter(
     final Class<? extends PersistentObject> clazz, final IObjectFilterProvider provider) {
   IObjectFilterProvider old = hash.get(clazz);
   if (old != null) {
     old.deactivate();
   }
   hash.put(clazz, provider);
   provider.activate();
   ElexisEventDispatcher.reload(clazz);
 }
 public void unregisterObjectFilter(
     final Class<? extends PersistentObject> clazz, final IObjectFilterProvider provider) {
   hash.remove(clazz);
   provider.deactivate();
   ElexisEventDispatcher.reload(clazz);
 }