code: public ServerNotificationRegistration getSpecificServerRegistration(RESTRequest request,
                                                                          int clientID,
                                                                          String source_objName,
                                                                          String listener_objName,
                                                                          String registrationID) {
          //Get the client area
          ClientNotificationArea clientArea = getInboxIfAvailable(clientID, null);
  
          List<ServerNotification> registrations = clientArea.getServerRegistrations(request, source_objName);
  
          if (registrations != null) {
              //Get the IDs from the request
              String[] artifacts = registrationID.split("_");
              int filterID = Integer.parseInt(artifacts[0]);
              int handbackID = Integer.parseInt(artifacts[1]);
  
              //loop registrations to match request
              for (ServerNotification registration : registrations) {
                  if (registration.listener.getCanonicalName().equals(listener_objName) &&
                      registration.filter == filterID &&
                      registration.handback == handbackID) {
                      //found a matching registration, so build and return filter/handback objects (could be null too)
                      ServerNotificationRegistration returningRegistration = new ServerNotificationRegistration();
                      returningRegistration.filter = (NotificationFilter) clientArea.getObject(filterID, null, null);
                      returningRegistration.handback = clientArea.getObject(handbackID, null, null);
                      return returningRegistration;
                  }
              }
          }
  
          return null;
      }
docs: Return the filter and handback that were registered for the given server-side notification, represented
  by the 3-tuple {source mbean, listener mbean, registrationID ID}.