code: public static String data(byte[] data, int offset, int length) {
          InputStream in = null;
          try {
              in = new ByteArrayInputStream(data, offset, length);
              return stream(in, length);
          } catch (IOException e) {
              e.printStackTrace();
          } finally {
              if (in != null) {
                  try {
                      in.close();
                  } catch (Exception e) {
                      e.printStackTrace();
                  }
              }
          }
          // never reach
          return null;
      }
docs: 计算二进制数据的etag
  
  @param data   二进制数据
  @param offset 起始字节索引
  @param length 需要计算的字节长度
  @return 二进制数据的etag