docs: public FileInfo stat(String bucket, String fileKey) throws QiniuException {
          Response res = rsGet(bucket, String.format("/stat/%s", encodedEntry(bucket, fileKey)));
          if (!res.isOK()) {
              throw new QiniuException(res);
          }
          FileInfo fileInfo = res.jsonToObject(FileInfo.class);
          res.close();
          return fileInfo;
      }