Hi everybody,

is it possible to safely use this patern with lazy initializing?

Consider the following:

1. Servlet application (Apache Tomcat).
2. one session per thread (using ThreadLocal class)
3. one session per request (I use a servlet filter to close the session).
4. one collection can be associated with one session - attempt to associate a collection with two open sessions will throw an exception (org.hibernate.HibernateException).

Now consider a JSP page, which needs to load an object with a collection. If you try to load the same object (with the same collection) in two threads, you probably get the exception.

My guess is, that if two users tryes to load the page in the same moment, Tomcat try to serve the two requests simultaneously in two threads and one of these users get the HibernateException.

Am I right?

If so, is there any way of using several sessions in Tomcat? I know only one solution - to have only one session and synchronize requests - but I consider it to be really a poor solution..

Many thanks

Regards
Tony

Each HTTP request will spawn it's own thread so ThreadLocal will work fine. The only time you would have a problem is when you attempt to load the same graph in the same Session, nothing to do with the thread, since each thread should have it's own ThreadLocal session.

I'm afraid you don't understand the problem.

Every thread has it's own session. But the problem occurs, when you try to load the same object to two threads (=two sessions).

So, the question is, whether is it possible to load a collection, which is already associated with another session...

Hmm. Maybe I'm being a little dense here, but there is no restriction or interaction between two separate and distinct sessions. The only problem you may encounter is if user A and user B both load the same object, make changes and then attempt to save. Then you would have to handle that concurrency issue in code, see http://www.hibernate.org/hib_docs/v3/re ... ctions.htm for info on that.

Many thakns.

After reading the chapter and writing some test-code I think, that I understand the topic a little :o)

Supriselly, I'm now not able to write a code, which thros the Exception:

org.hibernate.HibernateException: Illegal attempt to associate a collection with two open sessions

-- which is, what I initially tryed to figure out.

Do you know, in which configuration this exception occures?

Regads
Tony

I usually see this message when someone forgets to close a session. Especially prevalent in the Open Session in View "pattern".