code: public CdnResult.RefreshResult refreshUrlsAndDirs(String[] urls, String[] dirs) throws QiniuException {
          //check params
          if (urls != null && urls.length > MAX_API_REFRESH_URL_COUNT) {
              throw new QiniuException(new Exception("url count exceeds the max refresh limit per request"));
          }
          if (dirs != null && dirs.length > MAX_API_REFRESH_DIR_COUNT) {
              throw new QiniuException(new Exception("dir count exceeds the max refresh limit per request"));
          }
  
          HashMap<String, String[]> req = new HashMap<>();
          if (urls != null) {
              req.put("urls", urls);
          }
          if (dirs != null) {
              req.put("dirs", dirs);
          }
          byte[] body = Json.encode(req).getBytes(Constants.UTF_8);
          String url = server + "/v2/tune/refresh";
          StringMap headers = auth.authorizationV2(url, "POST", body, Client.JsonMime);
          Response response = client.post(url, body, headers, Client.JsonMime);
          return response.jsonToObject(CdnResult.RefreshResult.class);
      }
docs: 刷新文件外链和目录，外链每次不超过100个，目录每次不超过10个
  刷新目录需要额外开通权限，可以联系七牛技术支持处理
  参考文档：<a href="http://developer.qiniu.com/fusion/api/cache-refresh">缓存刷新</a>
  
  @param urls 待刷新文件外链列表
  @param dirs 待刷新目录列表
  @return 刷新请求的回复