Java Reference
In-Depth Information
} catch (Exception e) {
System.err.println(e.getMessage());
}
}
}
In EJB 3.0, a reference to a resource may be obtained with a dependency injection
with the
@EJB
annotation. JNDI lookup and
create()
method invocation is not
required in EJB 3.0. The client class for the EJB 3.0 session bean is listed next:
public class CatalogClient {
@EJB
CatalogBean catalogBean;
String publisher="OReilly";
String journal=catalogBean.getJournal(publisher);
System.out.println("Journal for Publisher: "+publisher +"
"+journal);
}
Simplified entity beans
An EJB 2.x Entity EJB bean class must implement the
javax.ejb.
EntityBean
interface, which defines callback methods
setEntityContext
,
unsetEntityContext
,
ejbActivate
,
ejbPassivate
,
ejbLoad
,
ejbStore
, and
ejbRemove
that are called by the EJB container. An EJB 2.x provides implementation
for the callback methods in the interface. An EJB 2.x entity bean also includes the
ejbCreate
and
ejbPostCreate
callback methods corresponding to one create
method in the home interface. An EJB 2.x entity bean's component and home
interfaces extend the
EJBObject/EJBLocalObject
and
EJBHome/EJBLocalHome
interfaces respectively. In comparison, an EJB 3.0 entity bean class is a POJO
which does not implement the
EntityBean
interface. The callback methods
are not implemented in the EJB 3.0 entity bean class. Also, the component and
home interfaces and deployment descriptors are not required in EJB 3.0. The EJB
configuration information is included in the Entity bean POJO class using metadata
annotations. An EJB 2.1 entity bean also consists of getter/setter
CMP
(
Container
Managed
Persistence
) field methods, and getter/setter
CMR
(
Container
Managed
Relationships
) field methods. An EJB 2.x entity bean also defines finder and
ejbSelect
methods in the home/local home interfaces for EJB-QL queries. An
example EJB 2.x entity bean is listed next:
import javax.ejb.EntityBean;
import javax.ejb.EntityContext;
public class CatalogBean implements EntityBean {
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