IllegalStateException: Cannot use an EntityTransaction while using JTA

Question

I'm making a project for school using JPA. I'm trying to persist an object but I'm getting an error I can't fix. I've read that I have to use usertransaction instead of entitytransaction but we didn't get much information during this lesson so I don't know a lot about this topic. How can I fix this error and be able to persist it?

This is the error I get:

java.lang.IllegalStateException: 
Exception Description: Cannot use an EntityTransaction while using JTA.

Here is the code that I use:

public class UserServiceImpl implements UserService {
    @PersistenceUnit
    private EntityManagerFactory emf = null;
    private EntityManager em = null;

    @Override
    public User register(User user) {        
        emf = Persistence.createEntityManagerFactory("Project_JavaPU");
        em = emf.createEntityManager();

        em.getTransaction().begin();
        em.persist(user);
        em.flush();
        em.getTransaction().commit();
        em.close();
        return user;
    }
}

Answer 1

I suggest to use a stateless EJB with a container-managed entity manager for transaction to be taken care of by JTA. See this Section in Java EE 6-Tutorial
Container-managed is just the easy way that is to be chosen over the more complex application-managed way except you have good reasons to do so.

Try this:

package containing.package;

import package.of.your.UserService

import java.io.Serializable;
import javax.ejb.Stateless;
import javax.persistence.EntityManager;
import javax.persistence.PersistenceContext;

@Stateless
public class UserServiceImpl implements UserService, Serializable {
    @PersistenceContext
    EntityManager em;

    @Override
    public User register(User user) {        
        em.persist(user);
        return user;
    }
}