code: public static HttpServiceTracker getServiceTracker(BundleContext context, String key, String value)
      {
          String filter = "(" + key + "=" + value + ")";
          try {
              ServiceReference[] references = context.getServiceReferences(ServiceTracker.class.getName(), filter);
              if ((references == null) || (references.length == 0))
                  references = context.getServiceReferences(ServiceTracker.class.getName(), null);   // Being paranoid
              if (references != null) {
                  for (ServiceReference reference : references)
                  {
                      Object service = context.getService(reference);
                      if (service instanceof HttpServiceTracker)    // Always
                          if (value.equals(((HttpServiceTracker)service).getProperty(key)))   // Being paranoid
                              return (HttpServiceTracker)service;
                  }
              }
          } catch (InvalidSyntaxException e) {
              e.printStackTrace();
          }
          return null;    // Not found
      }
docs: Get this service tracker.
  @param alias
  @return