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