Getting Database connection in pure JPA setup

As per the hibernate docs here,

Connection connection()

Deprecated. (scheduled for removal in 4.x). Replacement depends on need; for doing direct JDBC stuff use
doWork(org.hibernate.jdbc.Work) …

Use Hibernate Work API instead:

Session session = entityManager.unwrap(Session.class);
session.doWork(new Work() {

    @Override
    public void execute(Connection connection) throws SQLException {
        // do whatever you need to do with the connection
    }
});