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();
        }
    }