Java Reference
In-Depth Information
In progress: Successful event
After completion message: Successful event
After success message: Successful event
The onInProgress method is invoked immediately when the event is i red and while the transaction is
still in l ight. The other two methods— onCompletion and onSuccess —must wait until the transaction
reaches the AFTER _ COMPLETION and
AFTER _ SUCCESS phases, respectively, before they can execute.
Next you'll look at the getSixthChild method, which fails by causing an
IndexOutOfBoundsException . The output that results from calling this method follows:
In progress: Rollback event occurred.
Exception caught.
After completion message: Rollback event occurred.
After failure message: Rollback event occurred.
As before, the onInProgress method is invoked immediately, and the onCompletion and
onFailure methods must wait until the method completes. Once the onInProgress method
outputs the message Exception caught and the transaction is marked for rollback by
calling the SessionContext method setRollbackOnly , the y onInProgress method completes, and
you can execute your observers. The onCompletion method is executed, followed by the OnFailure
The setRollbackOnly method marks the current transaction for rollback, so it can never be
committed. This action triggers the transaction into the AFTER _ FAILURE
phase and invokes the
onFailure method.
Observers can also be given conditional behavior, although it's limited to being notii ed if an
instance of the bean that dei nes the observer method already exists in the current context.
The observer method is called only if an instance exists. To dei ne an observer method as
conditional, add notifyObserver = Reception.IF _ EXISTS as an argument to the @Observes
import javax.enterprise.event.Reception;
public void addMember (
@Observes( notifyObserver = Reception.IF_EXISTS ) String message){
// Implementation code.
The default behavior is to create an instance if it does not exist.
The observer pattern, which can unleash huge performance gains, is an effective way to promote
loose coupling and change the direction of calling/listening.
When designing your application or refactoring another's code, watch out for unnecessary and time
interval‐based method executions, which can be good candidates for implementing the observer pattern.
Search WWH ::

Custom Search