Question

How can I get an entity manager in a normal java class? I tried it with Injection, but without any result, I always get a NullPointerException:

public class ClassName {

    @PersistenceContext(unitName = "myPU")
    public EntityManager em;

    @Resource
    UserTransaction utx;

...

Then I tried it with a seperate class that provides the EntityManagerFactory, also without success, NullPointerException is thrown:

public class HibernateUtil {

    private static EntityManagerFactory entityManagerFactory = null;
    static {
        try {
            entityManagerFactory = Persistence.createEntityManagerFactory("myPU");
        } catch (Throwable e) {
            e.printStackTrace();
        }
    }

    public static EntityManagerFactory getEntityManagerFactory() {
        return entityManagerFactory;
    }
}

Help is appreciated.

Answer 1

public class ClassName {

    @PersistenceContext(unitName = "myPU")
    public EntityManager em;

    @Resource
    UserTransaction utx;

You have no Dependency.Injection here, if not running within a Java EE-Container.
These attributes are null. You need to initialize them first (Or add spring or another DI-container).