application managed persistence context

[Goran Markovic]

Hi
In every book I have read it have been written that application managed persistence context can be performed only in Stateful session beans. Is that correct?
I mean, you cannot span entity manager through multiple method of Stateless bean, or you can???
Well I thought that you can,. but I found this in ejb3_persistent_spec.

When an application-managed entity manager is used, the application interacts directly with the persistence
provider's entity manager factory to manage the entity manager lifecycle and to obtain and destroy
persistence contexts.
All such application-managed persistence contexts are extended in scope, and may span multiple transactions.

Considering this statement it mean that Stateless beans cannot be used, because they cannot be used in extended scope, right???
and then I found this piece of code, I believed that it could exists only in Stateful bean

@Stateless
public class ShoppingCartImpl implements ShoppingCart {
@PersistenceUnit
private EntityManagerFactory emf;
private EntityManager em;
@PostConstruct
public void init()
em = emf.createEntityManager();
}
public Order getOrder(Long id) {
Order order = (Order)em.find(Order.class, id);
em.clear(); // entities are detached
return order;
}
public Product getProduct() {
Product product = (Product) em.createQuery("select p from
Product p where p.name = :name")
.setParameter("name", name)
.getSingleResult();
em.clear();
return product;
}
public LineItem createLineItem(Order order, Product product, int
quantity) {
em.joinTransaction();
LineItem li = new LineItem(order, product, quantity);
order.getLineItems().add(li);
em.persist(li);
// persistence context is flushed to database;
// all updates will be committed to database on tx commit
em.flush();
// entities in persistence context are detached
em.clear();
return li;
}
@PreDestroy
public void destroy()
em.close();
}
}

Please, does anyone could clarified my doubts about this issue?
thanks

[Abraham Gimeno]

You can use an application-managed Entity Manager to gain more control over the transactions or the EM lifecycle.The container do the work transparently but this doesn't mean you can not interfere in it.

What it is doing the code you posted is basically the same it occurs at the background using a container-managed EM.