gwt-guice JPA, inject EntityManager thread safe?

[Yan]

Hi there, 

I need to deploy the app. to a J2EE container using JTA. So the annotation @Transactional does not work because it is using EntityTransaction, not compatible with JTA. 

To work around it, I inject UserTransaction which I acquire by JNDI lookup.   Is the following code thread-safe?  Since both EntityManager and UserTransaction are instance variables but the methods are run by multiple threads.

How can I make it thread-safe but still be able to use Injection?

Thanks,

Yan

import com.google.inject.persist.Transactional;
import javax.persistence.EntityManager; 
 
public class MyService {
        @Inject EntityManager em; 
        @Inject UserTransaction  // self-defined by JNDI look up 

        public void createNewPerson() {
                em.persist(new Person(...)); 
        } 

        public void createB() {

                em.persist(,,,)

        }

}

[Thomas Broyer]

Because a service is a quasi-singleton and you want your EntityManager request-scoped (session-per-request), you should inject a Provider<EntityManager> (I can't tell for UserTransaction as I don't know how it works)