I hope somebody can help me on the following problem;
My core business logic is implemented by means of Java code which is intended to run
in different middleware frameworks like EJB and COM/MTS. Consequently, there is no
knowledge in this Java code about which specific framework to be used to make the code
remote enabled, transactional etc.
The following example illustrates a pattern for how to EJB-enable code which is
EJB-unaware.
The core class A has a businessmethod doSmth() which - when executed - results in the
change of the attribute someAttribute. This attribute is persistent. The EJB class
EJBA is a wrapper of class A to remote-enable the business method, provide automatic
persistence under transaction control. The persistent attribute of A - someAttribute -
is mirrored in EJBA and EJBA delegates the business method call doSmth to A which in
turn fires propertyChangeEvents when the property someAttribute is changed.
The class PropagateEventsFromAtoEJBA implements propertyChangeListener and has the
responsibility of routing propertyChangeEvents from A to EJBA to ensure that
attributes are persisted.
The classes EJBA and PropagateEventsFromAtoEJBA are - in other words - classes
required to EJB-enable the EJB-unaware class A.
The connection between A and EJBA is constructed in EJBA in the following way when
EJBA is created or loaded:
-Instantiate A and set its persistent attributes
-Instantiate PropagateEventsFromAtoEJBA, provide it with the PrimaryKey of EJBA and
EJBAHome and register it as a propertyChangeListener of the A instance
class A{
.
.
int someAttribute;
.
void doSmth(){
update someAttribute;
firePropertyChangeEvent();
}
.
.
}
class EJBA implements EntityBean{
//This class is an EJB wrapper of A
//Business methods is delegated to A
int someAttribute; //Mirror of aRef.someAttribute
A aRef; //Reference to core class
.
.
//The business method doSmth. Delegates to aRef
void doSmth() throws RemoteException{
aRef.doSmth();
}
//This method is used by the PropagateEventsFromAtoEJBA class to
//prograte the propertyChangeEvent from A to EJBA
void propertyChange(PropertyChangeEvent pce){
//Use pce to find changed attribute and assign the
//new value to the mirrored attribute in EJBA
}
.
.
}
Now the problem: The design ensures that a persistent property being changed
in aRef.doSmth is updated in the EJBA.doSmth before this method returns, i.e. it is
persisted within the transaction context of the EJBA.doSmth method. The following
chain of method invocations takes place before EJBA.doSmth returns:
EJBA.doSmth->A.doSmth->PropagateEventsFromAToEJBA.propertyChange->EJBA.propertyChange
One major downside of this approach is that i requires the enterprise bean to be
re-entrant.
Can anybode provide an alternative, re-entrant free solution to this problem, still
ensuring that the attributes are persisted within the EJBA.doSmth method?
Thanks in advance,
J�rn Leonhardsen
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