Java Event handling

[Ranadhir Nag]

Can someone point me to a sample involving non-component based event handling?
All the samples that i find are event handlers being tied to AWT components?
I just wish to write a simple server which calls back on registered listeners(clients),by programmatically raising an event from one of the clients.
Any help will be appreciated.

[Edwin Dalorzo]

Have you taken a look to the java.util.Observer and java.util.Observable?

[Stan James]

I'm not a fan of Observer and Observable in the library. Before I even found them I made my own pub-sub with an intermediary. The flow is described HERE. I make an interface with methods for the events, implement it once in the intermediary and again in each subscriber. Here's an example with two events:

public class StartStopPublisher extends Publisher implements StartStopEvents
{
public void started()
{
Enumeration enum = subscribers();
while (enum.hasMoreElements())
{
StartStopEvents lSubscriber = (StartStopEvents) enum.nextElement();
lSubscriber.started();
}
}
public void shutDown()
{
Enumeration enum = subscribers();
while (enum.hasMoreElements())
{
StartStopEvents lSubscriber = (StartStopEvents) enum.nextElement();
lSubscriber.shutDown();
}
}
}

The abstract Publisher has (dead simple) methods to subscribe and unsubscribe. Some may be offended that I have to copy-paste that little loop for every event. But the flexibility I have here is pretty cool. I can pass parameters and get return types. I could let all the listeners vote on what to do next or let one of them signal that it has consumed the event and stop looping. I can have multiple publishers for the same event. Publishers can come and go while the subscription persists. Good fun.