Returns the SessionBroker that the Factory will be using and
initializes it if it is not available.
Calls to this method should only be made on entity managers
representing composite persistence units.
Gets the underlying implementation of the EntityManagerFactory.
This method will return a version of EntityManagerFactory that is
based on the available metadata at the time it is called. Future calls
to refresh will not affect that metadata on this EntityManagerFactory.
As this EntityManagerFactory to refresh itself. This will cause the
underlying EntityManagerFactory implementation to be dropped and a new one
to be bootstrapped. Existing EntityManagers will continue to use the old implementation