How to retrieve the Hibernate Session from the EntityManager interface

Sun, Jul 13, 2008

Well, as I myself fell into this stupid gap, I guess I’ll try to help. I was quite pushed in this trap by a fallacious part of the jboss documentation :

@PersistenceContext EntityManager entityManager;
public void someMethod();
{
  org.jboss.ejb3.entity.HibernateSession hs = (HibernateSession)entityManager;
  org.hibernate.Session session = hs.getHibernateSession();
}

Let’s be clear : this is totally WRONG! Yes, it will work under JBoss, but as there’s a standard way to do this, this is not the right way to do this.

In fact, there’s a dedicated method that lets you retrieve the underlying persistence manager : EntityManager.getDelegate(). If you read this method’s javadoc, you’ll see the following :

/**
 * Return the underlying provider object for the EntityManager,
 * if available. The result of this method is implementation
 * specific.
 * @throws IllegalStateException if this EntityManager has been closed.
 */
public Object getDelegate();

And the “underlying provider”, for Hibernate, is obviously the Hibernate Session instance…

So, the right way to retrieve the Session is something like the following instead :

@PersistenceContext EntityManager entityManager;
public void someMethod();
{
  org.hibernate.Session session = (Session)entityManager.getDelegate();
}

Under JBoss, using this code won’t make a big difference. But using the standard way will let you run your code under several appservers (namely, it works like a charm^[1]^ under JBoss 4.2.2.ga and Glassfishv2ur1 for example). If you use the bad way above, this will just crash under Glassfish, for example…

I reported the corresponding documentation bug in the JBOSS tracker.

Hope this helps…

Notes

[1] ça, c’est pour Seb

— Baptiste Mathus