Inject HttpService in an OSGi bundle in JBoss 7 - osgi

Question

I have a JBoss 7.1.2 application server up and running and now I wanted to deploy a OSGi bundle in it which registers a servlet. (kind of Hello World, but via a servlet)
Probably it is possible to archive this via a WAB, but as in OSGi, I thought it should also work in a simple, non wab bundle.
I created a bundle with an Activator as follows:
snip..
public void start(BundleContext bundleContext) throws Exception {
ServiceReference<?> httpServiceReference = bundleContext.getServiceReference(HttpService.class.getName());
System.out.println("ref: " + httpServiceReference);
HttpService httpService = (HttpService) context.getService(httpServiceReference);
System.out.println(httpService.getClass().getName());
try {
httpService.registerServlet("testservlet", new MyServlet() , null, null);
} catch (Exception e) {
e.printStackTrace();
}
}
After deploying and starting the bundle, the httpServiceReference is null.
I think this is strange, because when I look at the felix web console, there actually is HtttpService available. (from pax-web)
Does anyone know why my reference could be null here?
Thanks!

Answer 1

I think you are making the classical OSGi mistake. In the start(BundleContext context) method you are obtaining the reference to HttpService assuming its already started. The OSGi container starts bundles in some order. If your application bundle starts before the bundle that registers HttpService you will get a null reference. I suspect that's what is going on. You might be better off using ServiceTracker instead.
public void start(BundleContext bundleContext) throws Exception {
ServiceTracker httpServiceTracker = new ServiceTracker(bundleContext, HttpService.class, new ServiceTrackerCustomizer() {
#Override
public Object addingService(ServiceReference srf) {
HttpService httpService = bundleContext.getService(srf);
try {
httpService.registerServlet("testservlet", new MyServlet() , null, null);
} catch (Exception e) {
e.printStackTrace();
}
}
#Override
public void modifiedService(ServiceReference arg0, Object arg1) {
}
#Override
public void removedService(ServiceReference arg0, Object arg1) {
}
});
httpServiceTracker.open();
}