The attached patch adds a JpaPollingConsumer along with some unit tests.
I wasn't sure how to best factor out reusable logic between JpaConsumer & JpaPollingConsumer so I created JpaHelper (see TODO comment) & QueryFactoryBuilder. I didn't think inheritance was right there.
The patch only contains changes to JpaEndpoint. If you like the JpaHelper, I can patch JpaConsumer to make use of it as well.
Thanks for your patience,