public class MyIntegrator implements Integrator {

    public void integrate(Configuration configuration, SessionFactoryImplementor sessionFactory,
            SessionFactoryServiceRegistry serviceRegistry) {
        EventListenerRegistry listenerRegistry = serviceRegistry.getService(EventListenerRegistry.class);

        listenerRegistry.setListeners(EventType.MERGE, new MyMergeEventListener());
    }

    public void integrate(MetadataImplementor metadata, SessionFactoryImplementor sessionFactory,
            SessionFactoryServiceRegistry serviceRegistry) {
        // TODO Auto-generated method stub       
    }

    public void disintegrate(SessionFactoryImplementor sessionFactory, SessionFactoryServiceRegistry serviceRegistry) {
        // TODO Auto-generated method stub        
    }

    private static class MyMergeEventListener extends JpaMergeEventListener {

        private List<PersistentCollection> cleanCollections = new ArrayList<PersistentCollection>();

        @Override
        protected void copyValues(EntityPersister persister, Object entity, Object target, SessionImplementor source, Map copyCache) {
            Object[] origValues = persister.getPropertyValues(entity);
            Object[] targetValues = persister.getPropertyValues(target);
            Type[] types = persister.getPropertyTypes();

            // get Collections to be marked as clean
            // Do this BEFORE copyValues() is called, afterwards targetValues will be updated
            for (int i = 0; i < types.length; i++) {
                if (types[i].isCollectionType()) {
                    checkCollection((Collection) origValues[i], (PersistentCollection) targetValues[i]);
                }
            }

            super.copyValues(persister, entity, target, source, copyCache);

            // Reset the dirtyFlag of unmodified collections
            for (PersistentCollection col : cleanCollections) {
                col.clearDirty();
            }
        }

        private void checkCollection(Collection origValue, PersistentCollection targetValue) {
            Collection target = (Collection) targetValue.getValue();

            if (origValue.size() != target.size()) {
                return;
            }

            if (origValue.size() == 0 && target.size() == 0) {
                return;
            }

            if (origValue.containsAll(target)) {
                cleanCollections.add(targetValue);
            }
        }
    }
}