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();
    }
}