Hibernate 2.1.4 , Jboss 3.2.5

I have developed an application consisting of SSLB using Hibernate as the persistence layer. Each method in the SSLB uses the ThreadLocal pattern to get the session and close the session in the finally clause.

When a method doSomething() in SSLB1 calls method doThat() in SSLB2,
I get the following error : 'Session is closed'. How do I use the ThreadLocal pattern for nested calls?

Please advise.

How are you flushing and closing sessions? In each method?

What is your EJB transaction type?


Sherman

The EJB's are container managed. The sessions are flushed in each
method.

This is more difficult than it sounds. Some application servers (like JBoss) virtually guarantee that all EJB calls on the same node are made inside the same thread (pass by reference semantics). Others don't. I don't use much EJBs these days, so I would be interested in a solution or final answer to this question.

With ThreadLocal and calling multiple session bean methods, you have to have the current session be aware of the depth of the transaction calls (one transaction calls another. See Steve Ebersole's variation at http://www.hibernate.org/42.html.

Also check out http://www.jboss.org/wiki/Wiki.jsp?page=JBossHibernate. I haven't used the new stuff in JBoss 3.2.6 yet, but it look interesting.


Sherman

Thanks for the replies.

a) Is Steve Ebersole's approach safe? I am surprised that developers have not faced this common problem of nested CMT SSLB calls with Hibernate. The excellent book 'Hibernate in Action' does not have any references to this common problem.

b) Spring has inbuild support for sessions and transactions. Our project is not yet ready to tackle another framework.

c) I am interested in an appserver independent pattern for nested calls and session management.

My methods in the EJB's are

doSomething()
{
Session session = null ;

try
{

session = HibernateUtil.getSesssion() // ThreadLocal pattern

........ business logic ....

}
catch( Exception ex}
{

}
finally
{
HibernateUtil.closeSession();
}

}

As Christian notes, ThreadLocal works only for app servers that ensure a single thread through a transaction. I don't know what an app server independent solution would look like.

Steve's solution is safe if you ensure that you have your "open/closeSession" balanced, which finally helps with. There is nothing Spring specific in that.


Sherman

One of ways is to use custom proxy for SSLB and all app servers ensure a single thread through a transaction, I do not know broken servers, but do not care about broken server it does not work any way.

BTW see this code http://voruta.sourceforge.net/xref/samples/ejb/, implementation can be broken, but idea must be clear.

The conclusion I eventually came to is that nested ejb calls (at least prior to EJB 3) is a broken design. I wrote that wiki page when the architecture I was working on at that time did just that. But its not the right way to do this. The ejbs should simply delegate to classes which implement the actual functionality.

The code I wrote on the wiki does work as long as opens and closes are balanced like sgwood mentioned. If you are using JBoss and have the ability to upgrade to 3.2.6, use the session management stuff there instead. I (along with others) wrote that stuff also and it will work much better (re: more safely).

" The ejbs should simply delegate to classes which implement the actual functionality. "
This is recommended for all of RPC types, implement the actual functionality and generate RPC wrapper later, I prefer dynamic wrappers, but source code generation or templates like ATL was popular for C++ code in DCOM and CORBA too.