code: protected void checkForModifiedSince(MBeanServerExecutor pServerManager, JmxRequest pRequest)
              throws NotChangedException {
          int ifModifiedSince = pRequest.getParameterAsInt(ConfigKey.IF_MODIFIED_SINCE);
          if (!pServerManager.hasMBeansListChangedSince(ifModifiedSince)) {
              throw new NotChangedException(pRequest);
          }
      }
docs: Check, whether the set of MBeans for any managed MBeanServer has been change since the timestamp
  provided in the given request
  @param pServerManager manager for all MBeanServers
  @param pRequest the request from where to fetch the timestamp
  @throws NotChangedException if there has been no REGISTER/UNREGISTER notifications in the meantime