Hibernate - EntityManager management

Question

I am moving a JPA-Hibernate application from a Java EE 6 environment to a Tomcat 7 one.

The application has several DAO classes making queries on the EntityManager. In the Java EE environment I could just inject it using the @PersistenceContext annotation, and let the container manage the EntityManager. Now that I have to do it manually, I was wondering what is the way to go.

Should the entity manager be unique? If so can it be a static final field, created on startup and that every DAO class uses? Does it have a lifecycle that involves closing it and then re-opening it?

What do you mean, moving from Java EE 6 to Tomcat 7? Can you be more specific? — Zutty
– Zutty, Commented Jan 16, 2013 at 9:34
The application was running on glassfish, which is a JEE container, thus providing @PersistenceContext injection. Now the application will run on tomcat, which does not provide this mechanism. — kgautron
– kgautron, Commented Jan 16, 2013 at 9:53
If you for some reason or the other want to move away from GlassFish, why now move to TomEE? That's Tomcat as well, but with support for @PersistenceContext. — Arjan Tijms
– Arjan Tijms, Commented Jan 20, 2013 at 10:13

gcvt · Accepted Answer · 2013-01-16 10:03:30Z

2

Unfortunately, you'll have to do it manually. The way I usually do it is to define a special class:

public class EMF {
  private static EntityManagerFactory factory = Persistence.createEntityManagerFactory("name");

  public static EntityManager getEntityManager() {
    return factory.createEntityManager();
  }
}

So, every time you need EntityManager, you have to create it manually. You need to handle transactions as well:

EntityManager em = EMF.getEntityManager();
EntityTransaction et = em.getTransaction();
try {
  MyEntity my = new MyEntity();
  et.begin();
  try {
    em.persist(my);
    et.commit();
  } catch (Exception ex) { 
    if (et.isActive())
      et.rollback();
  }
} finally {
  em.close();
}

edited Jan 16, 2013 at 10:03

answered Jan 16, 2013 at 9:38

gcvt

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1 Comment

kgautron Over a year ago

So I need to create a new EntityManager everytime I access the database. Is that correct?

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