Implementing POJOs with EJB 3 - POJOs in Action: Developing Enterprise Applications with Lightweight Frameworks - page 363

They are intended to be the standard Java object persistence mechanism and can
be used both inside and out of the application server. EJB 3 persistence works out-
side the application server in the same way as JDO and Hibernate. Even if you are
only developing server applications, this is an extremely valuable feature because it
means that you can test entity beans without deploying them in the EJB container.
Simpler configuration
Another important improvement in EJB 3 is that you are no longer required to
write complex XML deployment descriptors to describe a bean's configuration.
Instead, EJB 3 lets you configure a bean using Java 5 annotations. An annotation is
a Java 5 language feature that associates extra data with a program element such
as a class or method. This data can be read by tools and frameworks such as the
EJB container. Annotations are often easier to use than an XML deployment
descriptor because they are located next to the program element that they
describe. What's more, because EJB 3 has sensible defaults for an EJB' s properties
you often only have to use a few annotations to turn a POJO into an EJB .
For example, the following code fragment shows the annotations on the
PlaceOrderFacade interface and PlaceOrderFacadeImpl class that will deploy the
PlaceOrderFacade from chapter 7 as a stateless session bean:
@Local
public interface PlaceOrderFacade {
…
}
@Stateless
public class PlaceOrderFacadeImpl
implements PlaceOrderFacade {
…
}
The @Local annotation specifies that the PlaceOrderFacade interface is a local EJB
interface, and the @Stateless annotation specifies that PlaceOrderFacadeImpl is a
stateless session bean. By default, its JNDI name is the fully qualified class name of
the local EJB interface and the EJB container uses container-managed transactions
with a transaction attribute of REQUIRED . If necessary, you can override the defaults
by using additional annotations. The EJB container reads the information speci-
fied by the annotations and uses it to deploy the EJB .
Configuring an entity bean is equally straightforward. You annotate the POJO
class with an @Entity annotation and annotate its fields or properties to map them
to the database. For example, here is part of the code for the PendingOrder EJB :