Event handling in java

I’m developing a web-based application that uses Java servlets to make RPC calls.
I’m searching for a solid technique to dispatch and handle server events. With a PHP application, I’m used to using Symfony’s EventDispatcher class to add event listeners and dispatch events, but I’m having trouble finding something analogous in Java because much of what I can find is about dealing with UI events, and I want to listen for and fire events on the server.

I’d also like the actual event handling to happen asynchronously on a separate thread or something, so that an API call to handle adding a payment can do what’s necessary, fire an event, and return immediately, even if the event triggers some more time-consuming stuff like sending emails or contacting a partner to inform them of the new balance.

Is it better to just write my own event interfaces, ExecutorService/Runnable, and Observer or Publish/Subscribe patterns? Or are there existing libraries (or built-in features I’m not aware of) that can handle some of this for me?
Thanks!