Hmmm... I've done some work within the JSP world, but not a ton. Anyways, let me take a stab at this.
First of all, we have trouble applying the observer pattern to a J2EE solution because, in order to implement the observer pattern, our subject must be able to invoke a method on the observer(s). This is difficult to visualize in J2EE because how would a subject (some object on the server) invoke a method on on a client (a web page)?
At first glance, I'd say that the observer pattern just doesn't fit into such a scenario, but it seems I'm just begging to be proven wrong. However, I just don't know how to "push" data to the client when Internet requests are generally "pull" oriented.
I imagine that you could have the client side poll for changes, but that kinda defeats the purpose of using an observer pattern, now doesn't it?
Certainly, if someone else knows a better answer to this, I'd love to hear it, as well.
Corey