Jersey, Guice and Hibernate - EntityManager thread safety

Question

I have used this tutorial them same way in my application: http://www.benmccann.com/hibernate-with-jpa-annotations-and-guice/

My app is JAX-RS web service which will

Answer 1

The problem was that my endpoint was annotated with @Singleton so it reused the same EntityManager during concurrent calls. After removing @Singleton, during concurrent calls, different EntityManager objects are used. If endpoint calls are subsequent, it may be that previous/old EntityManager will be used.

Highly simplified example:

@Path("/v1/items")
public class ItemsService {

    @Inject
    private EntityManager entityManager;

    @POST
    @Path("/{id}")
    @Consumes(MediaType.APPLICATION_JSON)
    @Produces(MediaType.APPLICATION_JSON)
    public void saveItem(){
         entityManager.getTransaction().begin();
         entityManager.persist(new Item());
         entityManager.getTransaction().commit();
    }
}

Answer 2

First of all, what kind of EntityManager are you using? Looking at your code I suposse this kind is Application-Managed EntityManager. It would be important for you to understand the different types of EntityManager.

Please see: http://docs.oracle.com/javaee/6/tutorial/doc/bnbqw.html

Basing on this, you need to create an EntityManagerFactory object and then create an EntityManager object.

Basic Example:

private static EntityManagerFactory emf; 
EntityManager em = null;

public static EntityManagerFactory getEmf(){
    if(emf == null){
        emf = Persistence.createEntityManagerFactory("nameOfYourPersistenceUnit");
    }
    return emf;
}


em = getEmf().createEntityManager();
em.getTransaction().begin();
em.persist(entity);
em.getTransaction().commit();
em.close();

Answer 3

If it says that the transaction is already open, that means that it was open by another process and not closed ...

I suggest to use @Transactionl instead of Writing :

em.getTransaction().begin();

and

em.getTransaction().commit();
em.close();

That will manage the things for you ...

so for you it will be this way :

@Transactionl
@POST
@Path("/{id}")
@Consumes(MediaType.APPLICATION_JSON)
@Produces(MediaType.APPLICATION_JSON)
public void saveItem(){
     entityManager.persist(new Item());
}

Hope that's help