JPA Project, TopLink Server session and ClassLoader issue

Question

hi,
I'm working on the project where JPA annotations are used to describe the mapping between POJOs and the database tables. JpaHelper class is used to bridge the gap between toplink-essentials and toplink. The EntityManagerFactory and the oracle.toplink.threetier.Server are obtained as following:
emf = JpaHelper.getEntityManagerFactory(Persistence.createEntityManagerFactory("myUnit"));
server = JpaHelper.getServerSession(emf);
Due to different functional and architectural constraints the same Server session has to be shared across different web applications. Thus the EntityManagerFactory has been bound to Weblogic JNDI tree and used by web applications to obtain Server session. It works very well for the very first client that is trying to query the data, but due to the fact that in the web container different web applications are using different ClassLoaders the QueryException “Missing descriptor for [class ...]” is being thrown for all consecutive call from other web applications. The same behaviour is observer after re-deploying the “first” application.
Going throughout different threads in the forum I learned that it could be solved for the "pure TopLink" projects where “sessions.xml” is used as following:
oracle.toplink.internal.helper.ConversionManager.getDefaultManager().setShouldUseClassLoaderFromCurrentThread(true);
boolean shouldLoginSession = true;
boolean shouldRefreshSession = true;
boolean shouldCheckClassloader = true;
session = SessionManager.getManager().getSession(new XMLSessionConfigLoader(), "mySession",
Thread.currentThread().getContextClassLoader(), false, true, true);
Could you please let me know if there is something similar for JPA projects where “sessions.xml” isn’t used or other options have to be considered?
regards,

Answer 1

I am not completely sure I understand what product and version you are using. TopLink Essentials and Oracle TopLink are independent products. They share the same heritage and much of the same functionality but typically you would only use one of them in an application.
If you have multiple web applications (WAR) that need to share the same JPA persistence unit I would package all of the JPA classes in their own JAR file and co-locate all of these WARs with the persistence JAR in a single EAR file. This should give you the capability to share the classes across the web applications.
Doug