Creating an EJB 3.0 Web Service - EJB 3.0 Database Persistence with Oracle Fusion Middleware 11g - page 392

The session bean class
The CatalogSessionEJBBean class is annotated with the annotation @Stateless .
The mappedName attribute specifies the global JNDI for the session bean. We shall
use the mapped name in the web service to look up the session bean and invoke
method/s on it. The @Remote annotation indicates that the session bean is a remote
interface:
@Stateless(name = "CatalogSessionEJB", mappedName = "EJB3-SessionEJB")
@Remote
public class CatalogSessionEJBBean implements CatalogSessionEJBRemote
{ }
Two types of EntityManager s are supported by the JPA: application-managed
EntityManager and container-managed EntityManager .
Container-managed EntityManager s always use JTA transactions, which
are managed by the EJB container and are created by injecting using the @
PersistenceContext annotation or by direct lookup of the entity manager in the
JNDI namespace.
Application-managed entity managers may use JTA or resource-local
transactions. Application-managed entity managers are created by injecting an
EntityManagedFactory with the @PersistenceUnit annotation and subsequently
invoking the createEntityManager() method on the EntityManagedFactory object.
We are using a container-managed entity manager. In the session bean, inject an
EntityManager using the @PersistenceContext annotation. One of the value-added
features of WebLogic Server 10.3 is that if the injected variable's name is the same
as the persistence unit, the unitName attribute of the @PersistenceContext or
@PersistenceUnit is not required to be specified, though we have specified it. The
type attribute is set to PersistenceContextType.TRANSACTION , which implies that
the persistence context is transaction-scoped.
@PersistenceContext(unitName = "em",
type = PersistenceContextType.TRANSACTION)
EntityManager em;
Add a method persistEntity() and a method test() to the session bean and the
remote interface. The persistEntity method is used to persist an entity using the
persist() method. Subsequent to persisting an entity instance, invoke the flush()
method to synchronize the entity manager with the database:
em.persist(entity);
em.flush();