websphere 7 and (application based) open-jpa 2 - persistence

Question

I want to not use the built in Websphere 7 jpa plugin, instead use an application WEB-INF/lib/open-jpa 2 and a proprietary persistence provider. I cannot install the OSGI and JPA 2 feature pack for Websphere.
Originally, I was getting a sax parse error simply trying to load the persistence.xml (version="2" not supported). The error was thrown by a class in open-jpa 1.2.3. When I run websphere/appserver/bin/wsjpaversion.bat, the open-jpa 1.2.3 jar is displayed. By default it overrides the open-jpa 2 jar in the app. I created a shared library containing the open-jpa 2 jar with this config option checked: 'Use an isolated class loader for this shared library'. I set my application classloader to load parent last and assigned it the new shared library resource. The 'version 2' error is gone, but there is another problem. When I try to initialize an EntityManager I get an error:
Caused by: javax.persistence.PersistenceException: Failed to load provider from META-INF/services
at javax.persistence.spi.PersistenceProviderResolverHolder$DefaultPersistenceProviderResolver.getPersistenceProviders(PersistenceProviderResolverHolder.java:121)
at javax.persistence.Persistence.createEntityManagerFactory(Persistence.java:91)
at java.lang.J9VMInternals.initializeImpl(Native Method)
at java.lang.J9VMInternals.initialize(J9VMInternals.java:200)
... 2 more
Caused by: java.lang.ClassCastException: com.ibm.websphere.persistence.PersistenceProviderImpl incompatible with javax.persistence.spi.PersistenceProvider
at javax.persistence.spi.PersistenceProviderResolverHolder$DefaultPersistenceProviderResolver.getPersistenceProviders(PersistenceProviderResolverHolder.java:110)
... 11 more
One more detail: inside the persistence.xml, the provider element is set to the proprietary PersistenceProviderImpl not the default Websphere persistence provider. So where is this websphere default coming from and how do I prevent it? (another important note: when I remove persistence.xml completely, I get the same error)
Thank you

Answer 1

Without installing the feature pack, you're fighting a losing battle. While it is possible to plug in your own JPA implementation, it is not possible to do that with JPA API — so WAS 7 ties you to the 1.0 version of JPA (see, for example, here how this is done — no class loader policy juggling will change that, though it seems tempting at first).