How do I use multiple databases with JPA?

Question

I need two or more than two connections in my web application using jpa

Answer 1

To use different data sources, add multiple persistence units (say, source-1 and source-2 in persistence.xml and create multiple EntityManagerFactoryes by name):

EntityManagerFactory emf1 = Persistence.createEntityManagerFactory("source-1");
EntityManagerFactory emf2 = Persistence.createEntityManagerFactory("source-2");

or, if you're working on Spring or Java EE application server, inject them by name also:

@PersistenceUnit(name = "source-1")
EntityManagerFactory emf1;

@PersistenceContext(unitName = "source-2") // as an option
EntityManager em2;

persistence.xml will thus look like the following:

Example of how to configure persistence unit, create EntityManager to manage entities and execute queries can be found here.