Avoiding Class.forName

[Guido Spadotto]

Title: Soluta Signature

Hi all,  I'm pretty new to OSGi, so I'd like you to give me some help (I've done my homework, but I'm a bit stuck). The problem: I have to write a service that listens to the org/osgi/framework/ServiceEvent/* topic to react to services being registered/unregistered. When a service event is fired to that topic, my service has to react to and handle only events that are related to services implementing *a given interface* (actually, extending a given class, but this will change in the future). My current solution is based on a DS component that extends EventHandler, whose handleEvent method is reported below (which I think is not the "correct" way to go): public void handleEvent(Event evt) {     //I know the event is a service event from the topic I'm listening to     ServiceEvent sEvt = (ServiceEvent) evt.getProperty(EventConstants.EVENT);                switch (sEvt.getType()) {         case ServiceEvent.REGISTERED:            // A service comes...            ServiceReference mySr = sEvt.getServiceReference();            Bundle containingBundle = mySr.getBundle();            BundleContext bc = containingBundle.getBundleContext();            Object service = bc.getService(mySr);            boolean isPssService = false;            try {              //TODO Ugly!              Class pssServiceClass = Class.forName(ServiceLocator.pssServiceClassName);              isPssService = pssServiceClass.isAssignableFrom(service.getClass());            } catch (ClassNotFoundException e) {              //Handle            }            if (isPssService){              //Another ugly casting              PssService pssService = (PssService) service;              ... do something ...            }else{              this.log(LogService.LOG_DEBUG, "Generic service registered");            }            break;         case ServiceEvent.UNREGISTERING:            // A service goes...            ... filter as above, then do something else...            break;         default:              this.log(LogService.LOG_WARNING, "Unhandled Service event: ("+ evt.getTopic() + ")");              break;     } } The questions: 1) Is there a way of filtering the handled events    to only those being fired by a service implementing    a given interface? At the moment, the only solution    to this requirement I'm aware of is by forcing the    registering/unregistering services to define a property    with a value to use in the "event.filter" service property. 2) Is there a standard pattern for retrieving and invoking the methods    from a service that caused a service event to be fired, starting    from the ServiceEvent itself, without using Class.forName to    downcast the BundleContext.getService(ServiceReference) result? 3) Am I supposed to call BundleContext.ungetService(ServiceReference)    while handling the ServiceEvent.UNREGISTERING event, to decrease    the context bundle's use count? Sorry for this lengthy mail, as you can see I have few ideas, and pretty confused. ;) Regards, -- Guido Spadotto Soluta.net, Italy http://www.soluta.net