code: public void listenerFlagUpdate(BackedSession d2) {
  
          if (_iStore.isHttpSessionListener()) {
              switch (d2.listenerFlag) {
                  case BackedSession.HTTP_SESSION_NO_LISTENER:
                      d2.listenerFlag = BackedSession.HTTP_SESSION_BINDING_LISTENER;
                      break;
                  case BackedSession.HTTP_SESSION_ACTIVATION_LISTENER:
                      d2.listenerFlag = BackedSession.HTTP_SESSION_BINDING_AND_ACTIVATION_LISTENER;
                      break;
                  default:
                      break;
              }
          }
      }
docs: /*
  listenerFlagUpdate
  This method ensures that the session is flagged as a listener if the the app
  has an HttpSessionListener. We need to know so we can call sessionDestroyed
  at invalidation time.
  
  The HTTP_SESSION_BINDING_LISTENER constant is overloaded and used for both
  HttpSession listener and Binding listener.