code: public boolean save(long max, OutputStream out) throws IOException {
          byte[] bytes = new byte[4096];
          int pos;
          InputStream in0 = this.getInputStream();
          while ((pos = in0.read(bytes)) != -1) {
              if (max < 0) return false;
              out.write(bytes, 0, pos);
              max -= pos;
          }
          return true;
      }
docs: 将文件流写进out， 如果超出max指定的值则中断并返回false
  
  @param max 最大长度限制
  @param out 输出流
  @return 是否成功
  @throws IOException 异常