[Springframework-developer] application event filters

[Keith D. <kei...@in...>]

Have we considered adding support for application event 
filters, to allow registered listeners to filter events of 
interest?  I think that would be a nice feature, and would 
be simplify listener handing code, as well as improve 
performance.
 
So for example, we could define the following interface:
 
public interface ApplicationEventFilter {
    public boolean isEventOfInterest(ApplicationEvent e);
}
 
public class LifecycleApplicationEventFilter {
    public boolean isEventOfInterest(ApplicationEvent e) {
        return (e instanceof LifecycleApplicationEvent);
    }
}
 
public interface ApplicationEventMulticaster {
    public void addApplicationListener(ApplicationListener 
listener, ApplicationEventFilter filter);
}
 
public class SimpleApplicationEventMulticaster {
 
        public void addApplicationListener
(ApplicationListener listener, ApplicationEventFilter 
filter) {
            this.applicationEventSubscriptions.add(new 
ApplicationEventSubscription(listener, filter));
        }
 
        public void multicastEvent(ApplicationEvent event) {
            Iterator it = 
this.applicationEventSubscriptions.iterator();
            while (it.hasNext()) {
                ApplicationEventSubscription subscription = 
(ApplicationEventSubscription) it.next();
                if (subscription.isEventOfInterest(event)) {
                    subscription.broadcast(event);
                }           
            }
        }
}
 
This is analagous to JMX's 
NotificationListener/NotificationFilter constructs