Wes was right to point you at Jan Hanneman's implementation, which solves
this problem rather elegantly.
You can find information on the Design Patterns project at:
http://www.cs.ubc.ca/~jan/AODPs/
Also, my forthcoming book Matering AspectJ
(http://www.amazon.com/exec/obidos/tg/detail/-/0471431044/)
contains a full writeup on this particular pattern, including a sample
application to the problem of cache invalidation.
Cheers,
Nick
--- "Enrique J. Amodeo Rubio" <eamodeorubio@xxxxxxxxxxxxxx> wrote:
Hi,
I have a question about aspect instantiation, how can I have an aspect
instance per each object of a determinated class? In this way we could
create an aspect like the following (some sintax, like perobject are
invented):
public abstract aspect SubjectObserverProtocol perobject(Subject+)
{
private Set observers = new HashSet();
public void notifyObservers(Event ev)
{
Iterator it=observers.iterator();
while(it.hasNext())
{
update((Observer)it.next(),ev);
}
}
public void addObserver(Observer o)
{
observers.add(o);
}
// follows point-cuts and advice to capture when is necesary to
// update the subject.
pointcut abstract updateObserver(Subject o,Event e);
protected abstract void update(Observer o,Event ev);
void after(Subject o,Event e) : updateObserver(o,e)
{
o.aspectOf().notifyObservers(e);
}
}
It should be a concrete aspect implementing updateObserver and update
method for each. Subject and Observer are empty interfaces. An important
point is avoiding collisions.
Does anybody know how to do this with aspectJ? Is necesary add more
functionality like the perobject keyword? Is there any work-around or
idiom? I feel there should be a good way to implement this kind of
functionality in an elegant way using aspectJ.
Thank you in advance,
Enrique J. Amodeo Rubio
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