Session Management with Java Hibernate

Question

I have a Hibernate-based platform, built from stateless servlets (one is used to register a user and the rest to query the db).

I'm using Hibernate's sessions as follows:

Session session = HibernateUtil.getSessionFactory().getCurrentSession();
if ((null == session) || (session.isOpen() == false)) {
  session = HibernateUtil.getSessionFactory().openSession();
}

Currently I do not close the session at the end of the servlet in order to avoid openSession() call (trying to use opened sessions if possible).

What's the best practice ? when am I supposed to close these sessions ?

Can you please give an example ?

Thanks in advance !

Answer 1

The best practice is in most cases session-per-request. That is, open a session in the beginning of handling a request, and close it in the end. You can do that in a Servlet Filter, for example.

Having one session for the entire application is bad, because it will accumulate a lot of entities in its 1st level cache, which is a memory leak. It may also produce undeterministic results when multiple clients use it at the same time.

Your code, however, is not using one session for the entire application - it is using the "current session" concept, which opens a session and stores it in a context (a ThreadLocal for example). But if you don't close it, it will stay there forever. Plus, it will cause the same problems as described above, because threads are reused in a web application, and a new request will get an old, unclosed session at some point.