//Create new ServiceTracker for HelloWorldService via HelloWorld interface
helloWorldServiceTracker = new ServiceTracker( context, HelloWorld.class.getName(), null );
//Service reference to ExtHttpService that will allows to register servlets and filters
ServiceReference sRef = context.getServiceReference( ExtHttpService.class.getName() );
if ( sRef != null ) {
helloWorldServiceTracker.addingService( sRef );
httpService = (ExtHttpService) context.getService( sRef );
try {