Hi,
I am using HibernateUtils for session management : the code is as follows

public class HibernateUtils {
static Logger log = Logger.getLogger(HibernateUtils.class);
public static final SessionFactory sessionFactory;

static {
try {

Configuration cfg = new Configuration().configure();
sessionFactory = cfg.buildSessionFactory();

} catch (Throwable ex) {
throw new ExceptionInInitializerError(ex);
}
}

public static final ThreadLocal<Session> session = new ThreadLocal<Session>();

public static Session getCurrentSession() throw HibernateException { Session s = (Session) session.get();
if (s == null) {
s = sessionFactory.openSession();
session.set(s);

System.out.flush();
}
return s;
}

public static void closeSession() throws HibernateException {
Session s = (Session) session.get();
if (s != null){
System.out.println("session is bieng closed here");
s.close();
System.out.flush();
}
session.set(null);
}
}

In the main application i am doing following things :

Session sess1 = HibernateUtils.getCurrentSession();
sess1.close();
Session sess2 = HibernateUtils.getCurrentSession();

and now i am getting the following exception::
Exception in thread "main" org.hibernate.HibernateException: Not able to obtain connection
at org.hibernate.jdbc.ConnectionManager.getConnection(ConnectionManager.java:113)
.....
.........................

and if i change the code as follows:

Session sess1 = HibernateUtils.getCurrentSession();
HibernateUtils.closeSession();
Session sess2 = HibernateUtils.getCurrentSession();
This time i am not getting exception. Why ???????

Sess1.close() and HibernateUtils.closeSession() both doing the same operation means closing the session. then why i am getting different behavior???????

In scenario @1:



Because your using a ThreadLocal and sess1 and sess2 referr to teh same session instance. Thus, closing sess1 is the same as closing sess2.

In scenario #2:



If you look at what you code is doing in your HibernateUtils class, the answer should be very clear :) Your HibernateUtils.closeSession() nulls out the ThreadLocal value and your HibernateUtils.getCurrentSession() returns a new Session when the ThreadLocal value is null.

This is why it's generally not a good idea to manually close a session when using CMT :)

Ryan-

Hi Ryan,

Thanks you for replying my post. It is confusing for me what you are trying to explain though it motivated me more and i tried to test the ThreadaLocal instance behavior and now i got the exact explanatiion why i was getting the exception.

Well thanks again for replying my post ( many guys had viewed but you only answered )
Thanks

A simplistic explanation would be that a ThreadLocal variable is kind of like an HttpSession or HttpRequest attribute. If you get an close the Session in one call, the next caller will get a close Hibernate Session.

Ryan-