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Hibernate version:
3.1.3

Do I have to close the session, or the JTA does it for me?

If I close the session, the sessionFactory.getCurrentSession() will open a new session, or reopen the closed one? How much expensive it is?

When using JTA, the Session is closed automatically on commit. There is a danger in closing a session that is returned by getCurrentSession(). If you have 2 or more components involved in a transaction which load data via Hibernate. Suppose that component 1 loads data 1st and calls session.close(). When component 2 call getCurrentSession(), an exception will be thrown stating that the session was closed.

In short: when using a JTA managed SessionFactory let Hibernate do the closing.

Ryan-

Thanks,
I was a bit confused, because some said that session object must always be closed at the end of the work, and "in a CMT enviroment you must close if for safety".
I think in case of HibernateException I have to call the session.close() haven't I?

Nope. When a RuntimeException is thrown in a CMT environment, the transaction is automaticaly rolled back. HibernateException is a RuntimeException and when the transaction is rolled back, the Session is closed. I can confirm this is true with Hibernate 3.1 under JBoss 4 and WLS 8.1. under Hibernate 2.x, you did have to close the session manually. This is no longer true for 3.1.

Ryan-

Remember that hibernate 3.x in a CMT environment implements (and binds) transaction lifecycle interceptors, which are in charge of mantaining resource and session consistency across the different stages of a transaction.

According to the help doc Sessions and Transactions you don't need to close the session.

Guido Scalise