suggestions for externalizing code flow of j2ee app

[Ittay]

Hi,

I'm looking for a way to externalize the flow of a j2ee application.
What I mean is that if traditionally, I'd write a flow of some
functionality by having methods calling each other, then I'm looking
for some declerative (xml) way of doing that. So that the flow can be
modified externally, by plugging other pieces of code into it, perhaps
replacing existing ones, that can modify the flow.

Another thing is that the flow is not synchroneous. To acheive some
functionality, several execution threads are needed (one after the
other)

Thanks,
Ittay