code: private static String resultEncode(byte[][] sha1s) {
          byte head = 0x16;
          byte[] finalHash = sha1s[0];
          int len = finalHash.length;
          byte[] ret = new byte[len + 1];
          if (sha1s.length != 1) {
              head = (byte) 0x96;
              MessageDigest sha1 = null;
              try {
                  sha1 = MessageDigest.getInstance("sha-1");
              } catch (NoSuchAlgorithmException e) {
                  e.printStackTrace();
                  // never reach
                  return null;
              }
              for (byte[] s : sha1s) {
                  sha1.update(s);
              }
              finalHash = sha1.digest();
          }
          ret[0] = head;
          System.arraycopy(finalHash, 0, ret, 1, len);
          return UrlSafeBase64.encodeToString(ret);
      }
docs: 合并结果
  
  @param sha1s 每块计算结果的列表
  @return 最终的结果