使用Java Hibernate进行会话管理

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.

Answer 2

Its always better to open a new session for every request, and close the session once the request is processed. Like

Session session = HibernateUtil.getSessionFactory().openSession();

instead of

Session session = HibernateUtil.getSessionFactory().getCurrentSession();

If we use the getCurrentSession() method , tansaction.commit() / rollback() closes the connection.

Answer 3

The best is to manage a hibernate session is to open a new session for every request. It all depends on how you obtain the session.

• if you use sessionFactory.getCurrentSession(), you'll obtain a "current session" which is bound to the lifecycle of the transaction and will be automatically flushed and closed when the transaction ends (commit or rollback)
• if you decide to use sessionFactory.openSession(), you'll have to manage the session yourself and to flush and close it "manually".

 if (!session.isOpen()) { session = session.getSessionFactory().openSession(); session.beginTransaction(); } 

Answer 4

I better recommend you to use spring framework. Cause in spring you can use @Transactional at method level and session will be automatically created and closed by transaction manager (unless you are using any open session in view interceptor) using AOP which is internally handled by framework.

@Autowired
EntityManager em;

@Transactinal
void save(User user){
   em.persist(user);
}

thats all.spring is fun :D