code: public String getGroupIdByOpenid(String openid) {
          BeanUtil.requireNonNull(openid, "openid is null");
          LOG.debug("通过关注者ID获取所在分组信息.....");
          String result = null;
          String url = BASE_API_URL + "cgi-bin/groups/getid?access_token=#";
          Map<String, String> params = new HashMap<String, String>();
          params.put("openid", openid);
          BaseResponse r = executePost(url, JSONUtil.toJson(params));
          if (isSuccess(r.getErrcode())) {
              result = JSONUtil.toMap(r.getErrmsg()).get("groupid").toString();
          }
          return result;
      }
docs: 通过关注者ID获取所在分组信息
  
  @param openid 关注者ID
  @return 所在分组信息