Inject a EntityManagerFactory through @PersitenceContext or @PersitenceUnit?

Question

I've always thought that @PersistenceContext was for injecting EntityManager into a container-managed application, while @PersistenceUnit was for injecting an EntityManagerFactory.

Javadoc says

For PersistenceUnit (http://docs.oracle.com/javaee/7/api/javax/persistence/PersistenceUnit.html)

Expresses a dependency on an EntityManagerFactory and its associated persistence unit.

And for PersistenceContext (http://docs.oracle.com/javaee/7/api/javax/persistence/PersistenceContext.html)

Expresses a dependency on a container-managed EntityManager and its associated persistence context.

So far so good, but then I was reading the JPA tutorial (see https://docs.oracle.com/cd/E19798-01/821-1841/bnbqy/index.html) that contains an example like this

The following example shows how to manage transactions in an application that uses an application-managed entity manager:

@PersistenceContext
EntityManagerFactory emf;
EntityManager em;
@Resource
UserTransaction utx;
...
em = emf.createEntityManager();
try {
  utx.begin();
  em.persist(SomeEntity);
  em.merge(AnotherEntity);
  em.remove(ThirdEntity);
  utx.commit();
} catch (Exception e) {
  utx.rollback();
}

so the PersistenceContext can also refer to an EntityManagerFactory if we're talking about an application managed code?

disclaimer -- not related to the answers from this question I guess -- PersistenceUnit vs PersistenceContext

Answer 1

I've always thought that @PersistenceContext was for injecting EntityManager into a container-managed application, while @PersistenceUnit was for injecting an EntityManagerFactory.

That's true.

I guess the example of the JPA tutorial is a careless mistake. Previously in the same section 'Application-Managed Entity Managers' it's written

To obtain an EntityManager instance, you first must obtain an EntityManagerFactory instance by injecting it into the application component by means of the javax.persistence.PersistenceUnit annotation:

@PersistenceUnit EntityManagerFactory emf;

Then obtain an EntityManager from the EntityManagerFactory instance:

EntityManager em = emf.createEntityManager();