OC4J Class Loaders for Servlets

Question

Hi all,
I know that servlets running in certain servlet engines (iPlanet for example) are loaded by different class loaders.
Since I'm trying to define a singleton class which shares data commont to all my servlets, I realized that OC4J uses different class loaders for different servlets; as a consequence, different servlets accessing my singleton class get two different objects.
This conjecture comes from the fact that using
System.identityHashcode(myClass.class.getClassLoader())
I get different codes when running different JSP.
Can someone from Oracle confirm my thoughts?
TIA
Maurizio

Answer 1

Hello,
It looks like you may need to find an appropriate class loader in your application for toplink.
First, let us clarify assumptions:
1. Your session bean (which is, I assume managing your TopLink persistent objects) is in an ejb.jar by itself.
2. Your application and TopLink enabled persistent classes are in a separate jar.
3. Your web interface is in a war by itself.
4. This package is bundled, complete, in an ear file and deployed as a single unit in oc4j.
5. TopLink is supplied as an oc4j level library by adding the xerces.jar and wdiall.jar in the lib directory. (antlr too if you want ejbql).
6. Your code is using the sessions.xml technique for initializing TopLink.
Having made all these assumptions about your code, the only thing you need to do to make your application work with all the various class loaders is instead of calling SessionManager.getManager().getSession("mySession"), call SessionManager.getManager().getSession("mySession",MyApplicationClassFromMyApplicationClassJar.class.getClassLoader());
This should resolve your problem. Generally, the above 6 assumptions are an approved way of structuring an application that uses session beans and TopLink for deployment in oc4j. Other ways can be made to work similarly by finding a class which has the right classloader on it. One requirement is that the class loader can see everything for the TopLink project, not just portions of it.
I hope this deluge of information helps,
Christian Weeks