This
article shows the common Service Facade pattern in the EJB context. Several
aspects takes into account this pattern.
1) The
Service Facade insolates the service definition from its implementation.
2) It is
the way of decoupling the Web tier from the Business tier.
3) From a
transactional point of view, the business service may implement his transaction
scope or be part of the current transaction.
4) The contract
of the Service Facade interface is oriented to be invoked by Web tier or client
software, but methods of the contract should not be invoked within the business
implementation.
The
following is an example of this pattern.
Firstly, an
interface with the contract definition is defined:
@Local
public interface FarewellBusiness {
public void sendMessage(String message);
public void sendMessageDetail(String message,String
detail);
}
Secondly, a class that implements this
interface is created. This class is the Stateless bean that will be managed by
the JEE-container.
@Stateless (name="farewellBusiness")
@Clustered
@TransactionAttribute (TransactionAttributeType.REQUIRES_NEW)
public class FarewellBusinessBean implements FarewellBusiness {
@Inject FarewellBusinessLogic
business;
public void sendMessage(String message) {
business.sendMessage(message);
}
public void sendMessageDetail(String message,String
detail)
{
business.sendDetailForMessage(message, detail);
}
}
As the
class reflects :
@Stateless:
It is a stateless java bean.
@Clustered:
It is executed within a JBoss cluster (for instance)
@TransactionAttribute (REQUIRED_NEW). Invocations of methods
of this class require a transaction scope. If there is already a transaction
scope running, the instance is executed under the transaction scope, if not; a
new transactional process is created.
The
invocation of the EJB is by way of the Service Interface, as the example below
shows:
@ManagedBean (name="manager")
@SessionScoped
public class ManagerBean implements Serializable{
@ManagedProperty(value="#{farewell1}")
FarewellBean
bean;
@EJB
FarewellBusiness
farewellBusiness;
public String send(){
// send the message invoking business ejb
farewellBusiness.sendMessage(bean.getFarewell1());
return "success";
}
public void setBean(FarewellBean
bean) {
this.bean = bean;
}
public String sendDetail(){
farewellBusiness.sendMessageDetail(bean.getFarewell1(), bean.getDetail());
return "success";
}
}
