update using JPA

Question

Hi I m using glassfish v2 and persistence in a web application.

I m calling persistence codes using a normal java class file inside a web Application

I can select easily using this code: -

   @PersistenceUnit
public EntityManagerFactory emf;
EntityManager em;


public List fname (String id) {
    String fname = null;
    List persons = null;
    //private PersistenceManagerFactory persistenceManagerFactory;

    try {
        emf = Persistence.createEntityManagerFactory("WebApplicationSecurityPU");

        em = emf.createEntityManager();
        persons = em.createQuery("select r from Roleuser r").getResultList();

        int i=0;
        for (i=0;i<persons.size(); i++)
            System.out.println("Testing n "+ i +" " + persons.get(i));

    } catch(Exception e) {
        System.out.println("" + e);
    }
    finally {
        if(em != null) {
            em.close();
        }
    }
    return persons;
}

I want to update using JTA as the persistence.xml file has transaction-type="JTA"

When i try using update using this code i get a nullPointerException without any traces in the log

     @PersistenceUnit
public EntityManagerFactory emf;
EntityManager em;
Context context;
@Resource
private UserTransaction utx;

public List fname (String id) {

    String fname = null;
    List persons = null;


    try {
        emf = Persistence.createEntityManagerFactory("WebApplicationSecurityPU");

        utx.begin();
        em = emf.createEntityManager();

        int m = em.createQuery("update Roleuser r set r.firstName = 'Jignesh I' where r.userID=9").executeUpdate();

        utx.commit();


    } catch(Exception e) {
        System.out.println("" + e);
    }
    finally {
        if(em != null) {
            em.close();
        }
    }
    return persons;
}

Any help

Thanks

Pradyut

Answer 1

1. Perhaps your bean isn't managed - i.e. it's not part of any context (spring, EJB). How are you creating your object?
2. You really should not call createEntityManager() - inject one using @PersistenceContext
3. You must be absolutely sure you need JTA before using it.
4. You seem to be using PersistenceUnit, but then re-assign the etm - I'd suggest drop both and see p2 above.

If you are not using any dependecy injection at all, then drop all the annotations, retain the current code, and type:

em.getTransaction().begin();
...
em.getTransaction().commit();

(and define RESOURCE_LOCAL in your persistence.xml. You really don't need JTA)

Answer 2

well the code should be without any nightmares...(atleast for me in glassfish)
with the persistence.xml having

<persistence-unit name="WebApplicationSecurityPU" transaction-type="RESOURCE_LOCAL">

the code

@PersistenceUnit
public EntityManagerFactory emf;
public EntityManager em;




public EntityManager getEm() {
    emf = Persistence.createEntityManagerFactory("WebApplicationSecurityPU");
    em = emf.createEntityManager();
    return em;
}

public List fname (String id) {

    String fname = null;
    List persons = null;


    try {
        System.out.println("test");

        em = this.getEm();


        em.getTransaction().begin();
        int m = em.createQuery("update Roleuser r set r.firstName = 'Jignesh H' where r.userID=9").executeUpdate();

        em.getTransaction().commit();


    } catch(Exception e) {
        System.out.println("" + e);
    }
    finally {
        if(em != null) {
            em.close();
        }
    }
    return persons;
}

Any improvements are welcome...(actually needed...) (How to go about using @PersistenceContext)

Thanks

Pradyut

Answer 3

Your "normal" class is very likely not a managed component i.e. a class whose life cycle is managed by the container (like Servlets, Servlet Filters, JSP tag handlers, JSF Managed Beans, ...) and can't benefit from resource injection¹. So neither the UserTransaction nor the EntityManagerFactory are injected here, hence the NullPointerException.

Honestly, you should try to use a container managed EntityManager, this would make your code less messy. If you cannot get it injected, get it via a JNDI lookup. See the resource below.

_{¹ Have a look at Web Tier to Go With Java EE 5: A Look at Resource Injection for a nice overview of what can be injected, and where.}

Resources

• How to use EntityManager API in web module

References

• JPA 1.0 specification
  • Section 5.2 "Obtaining an Entity Manager"
  • Section 5.6 "Container-managed Persistence Contexts"