code: public void addChain(String httpMethod, ActionChain chain) {
          if (Strings.isBlank(httpMethod))
              throw Lang.makeThrow("chain need a valid HTTP Method, but is is '%s'", httpMethod);
          ActionChain old = chainMap.put(httpMethod.toUpperCase(), chain);
          if (old != null) {
              log.warnf("Duplicate @At mapping with same HttpMethod");
          }
      }
docs: 增加 ActionChain
  
  @param httpMethod
  HTTP 的请求方法 (GET|POST|PUT|DELETE),如果为空，则会抛错
  @param chain
  动作链