I managed to get JPA2.0 working in Weblogic in a slightly different way then what is described in "DI 1.1: Alternative 3: Application Level Shared Library".
- I did not put anything in APP-INF/lib neither in war/WEB-INF/classes/META-INF/MANIFEST.MF
- at first Weblogic was still trying to parse my persistence.xml that is inside war/WEB-INF/classes/META-INF, this happened before Spring initialization started, so at that point my application was not even trying to use JPA
- to fix this I renamed it to persistenceWeblogic.xml and changed the Spring configuration to use this name instead of the default
For me it looks like Weblogic was just validating the persistence.xml, so by renaming it this validation was disabled.