Re: [hibernate-dev] Overriding JpaMergeEventListener with JpaEntityCopyAllowedMergeEventListener

From: "Gail Badner" <gbadner(a)redhat.com&gt; To: "Steve Ebersole" <steve(a)hibernate.org&gt;, "Emmanuel Bernard" <emmanuel(a)hibernate.org&gt; Sent: Friday, June 20, 2014 4:25:56 PM Subject: Overriding JpaMergeEventListener with JpaEntityCopyAllowedMergeEventListener I am trying into figure out how to override JpaMergeEventListener with JpaEntityCopyAllowedMergeEventListener as described in [1]. This documentation does not describe how to deal with injecting CallbackRegistry into an overridden MergeEventListener. CallbackRegistry is an SPI, but JpaMergeEventListener and CallbackRegistryConsumer are internal. JpaEntityCopyAllowedMergeEventListener is also internal. I was planning to document MyIntegrator.integrate(..) for enabling entity copies, but I don't like the idea of documenting an internal event listener for that functionality. Here is one alternative that minimizes exposing private classes/methods: public class MyIntegrator implements org.hibernate.integrator.spi.Integrator { public void integrate( Configuration configuration, SessionFactoryImplementor sessionFactory, SessionFactoryServiceRegistry serviceRegistry) { final EventListenerRegistry eventListenerRegistry = serviceRegistry.getService( EventListenerRegistry.class ); final MergeEventListener mergeEventListener = mergeEventListenerGroup.listeners().iterator().next(); final JpaEntityCopyAllowedMergeEventListener entityCopyAllowedMergeEventListener = new JpaEntityCopyAllowedMergeEventListener(); entityCopyAllowedMergeEventListener.initializeFrom( mergeEventListener ); registry.setListeners( EventType.MERGE, entityCopyAllowedMergeEventListener ); } ... } public class JpaEntityCopyAllowedMergeEventListener extends JpaMergeEventListener { ... public void initializeFrom(MergeEventListener mergeEventListener) { if ( JpaMergeEventListener.class.isInstance( mergeEventListener ) ) { injectCallbackRegistryFrom( (JpaMergeEventListener) mergeEventListener ); } } ... } public class JpaMergeEventListener extends DefaultMergeEventListener implements CallbackRegistryConsumer { ... protected void injectCallbackRegistryFrom(JpaMergeEventListener jpaMergeEventListener) { injectCallbackRegistry( jpaMergeEventListener.callbackRegistry ); } ... } Another alternative is to change JpaEntityCopyAllowedMergeEventListener to be a Proxy that holds an instance of the original JpaMergeEventListener. Everything except for createEntityCopyObserver() could be delegated to the stored JpaMergeEventListener. There would be no need to call injectCallbackRegistry(CallBackRegistry). It might be possible to have one Proxy for JpaEntityCopyAllowedMergeEventListener and EntityCopyAllowedMergeEventListener holding an instance of MergeEventListener, but that Proxy wouldn't implement CallbackRegistryConsumer or HibernateEntityManagerEventListener. Does that matter for an overridden event listener if the CallbackRegistry does not have to be injected? Is there some other way of doing this that I've missed? Thanks, Gail [1] http://docs.jboss.org/hibernate/orm/4.3/devguide/en-US/html/ch07.html#reg...