Guava's EventBus - Simple Publisher/Subscriber

The event bus is one of my very favorite architecture patterns.

It usually ends up in most desktop apps I write that have a UI. There's just too much to love about them. In languages with method annotations (or something similar), the wiring process can be almost entirely automatic.

I would usually use Akka for that kind of thing: http://akka.io (I've rolled my own before, too)

GWT has had a similar EventBus class for a while that works well on both the server and client sides of an app.