Question

I am trying to run a demo application for OSGi EventAdmin service, but the EventHandler I implemented fails to listen the events posted by the EventAdmin publisher:

Below is the code for Event Publisher, followed by the code for Listener(EventHandler):

public class Publisher implements BundleActivator{

static EventAdmin eventAdmin;
ServiceReference ref;
static HashMap properties= null;

@Override
public void start(BundleContext context) throws Exception {
    ref=context.getServiceReference(EventAdmin.class.getName());

    if(ref==null){
        System.err.println("Unable to aquire EventAdmin Ser Ref.");
    }

    eventAdmin=(EventAdmin) context.getService(ref);
    if(eventAdmin==null){
        System.err.println("unable to get service:EventAdmin");
    }

    properties=new HashMap();
    properties.put("XYZ", "Test");
    Event event = new Event("lnu/test/event/Demo", properties);
    eventAdmin.postEvent(event);
    System.out.println("event posted");

}

@Override
public void stop(BundleContext context) throws Exception {
    // TODO Auto-generated method stub
}
}

Code for Listener:

public class Listener implements BundleActivator, EventHandler {    

public void start(BundleContext context) {
Dictionary d = new Hashtable();

d.put(EventConstants.EVENT_TOPIC, "lnu/test/event/Demo" );

context.registerService( EventHandler.class.getName(),
this, d );
System.out.println("event handler is registered now");
}

public void stop( BundleContext context) {}

public void handleEvent(Event event ) {
System.err.println("Event has been captured");
System.out.println("getTopic: "+event.getTopic());
System.out.println("getproperty: "+event.getProperty("XYZ"));
}
}

The print statements in the code show that the event has been posted by the publisher and the Listener is registered with the EventHandler service but still it does not invokes handleEvent method on the listener side, I don’t know why? and can’t understand what is happening behind the scene. There are no runtime exceptions/errors.

The IDE used is Eclipse Juno Build id: 20120614-1722 with Equinox.

Following Target Platform bundles are included in the run configuration:

1. org.eclipse.osgi
2. org.eclipse.equinox.event
3. org.eclipse.equinox.util
4. org.eclipse.osgi.services

Can some one point me what I am missing or doing wrong? Or if you have some link to working example of OSGi EventAdmin service?

Answer 1

I would guess that your listener bundle is being registered after the publisher bundle has already posted the Event.

Testing this in the start methods of the bundles is error prone for this reason unless you control the start order of the bundles. I would suggest for this simple test that you start a separate thread in your publisher to post an event every few seconds. The listener should start getting them once it is registered.