JPA build entity manager with a specific JDBC connection instance

Question

I want to manage the database connection outside entity manager context so that I can use it for different entity managers. The question is how can I build the entity manager factory or entity manager with my own connection instead of providing it with properties in persistence.xml?

Answer 1

In either case the answer is that you cannot, in SE you can specify the db connection properties when creating the EntityManagerFactory, but the db connection is still maintained by the EntityManager and for good reason, if you controlled this you could commit and rollback behind the EntityManager's back. If you gave the same db connection to multiple EntityManager's this would be chaos indeed, I am not sure why on earth you want to do this.

The best I can suggest is that you look into the EntityManager.getDelegate() (JPA 1.0) or EntityManager.unwrap(java.lang.Class cls) (JPA 2.0) methods they may return the underlying provider (ie. Hibernate) object which you may be able to pry the database connection out of, but you certainly won't be able to replace it.

In short really bad idea.