code: @Override
      public byte[] get(String key) {
          File f = new File(directory, hash(key));
          FileInputStream fi = null;
          byte[] data = null;
          int read = 0;
          try {
              if (outOfDate(f)) {
                  f.delete();
                  return null;
              }
              data = new byte[(int) f.length()];
              fi = new FileInputStream(f);
              read = fi.read(data);
          } catch (IOException e) {
              e.printStackTrace();
          }
          if (fi != null) {
              try {
                  fi.close();
              } catch (IOException e) {
                  e.printStackTrace();
              }
          }
          if (read == 0) {
              return null;
          }
          return data;
      }
docs: 获取分片上传进度
  
  @param key 上传文件进度文件保存名