code: public void acceptGateway(MessageResourcesGateway specified) {
          logger.info("...Accepting the gateway of message resources: " + specified);
          if (specified == null) {
              String msg = "The argument 'specified' should not be null.";
              throw new IllegalArgumentException(msg);
          }
          if (gateway != null) {
              String msg = "The gateway already exists: existing=" + gateway + " specified=" + specified;
              throw new IllegalStateException(msg);
          }
          gateway = specified;
      }
docs: Accept the gateway for message resources. <br>
  You should call this immediately after your application is initialized. <br>
  And only one setting is allowed.
  @param specified The instance of gateway. (NotNull)