code: public static String longToHexBytes(final long v) {
      final long mask = 0XFFL;
      final StringBuilder sb = new StringBuilder();
      for (int i = 8; i-- > 0; ) {
        final String s = Long.toHexString((v >>> (i * 8)) & mask);
        sb.append(zeroPad(s, 2)).append(" ");
      }
      return sb.toString();
    }
docs: Returns a string of spaced hex bytes in Big-Endian order.
  @param v the given long
  @return string of spaced hex bytes in Big-Endian order.