How to create a thread safe EntityManagerFactory?

Question

I'm working on an application that needs to do some database operations.

I created a static variable for EntityManagerFactory and initializeded it in the method that gets called by the application

 if (emf == null) {
      emf = Persistence.createEntityManagerFactory("example");
 }

 try {
      em = emf.createEntityManager();
 } catch (Exception ex) {
      logger.error(ex.getMessage());
 }

Is this thread-safe? If I create the EntityManagerFactory in a synchronized block, the number of the waiting threads increases and crashes the application.

I looked at the docs to see whether the Persistence.createEntityManagerFactory is thread-safe without any success.

Please direct me to the right resources.

Answer 1

An easy way to "solve" this would be to use a helper class (a la HibernateUtil) and to initialize the EntityManagerFactory in a static initialization block. Something like this:

public class JpaUtil { 
    private static final EntityManagerFactory emf;

    static {
        try {
            factory = Persistence.createEntityManagerFactory("MyPu");
        } catch (Throwable ex) {
            logger.error("Initial SessionFactory creation failed", ex);
            throw new ExceptionInInitializerError(ex);
        }
    }

   ...

}

And the "problem" is gone.