code: public static String base64FromHex(String hexValue) throws IllegalArgumentException {
          byte[] binary = DatatypeConverter.parseHexBinary(hexValue);
          return base64FromBinary(binary);
      }
docs: Decode the given hex string to binary and then re-encoded it as a Base64 string.
  
  @param hexValue                  String of hexadecimal characters.
  @return                          Decoded binary value re-encoded with Base64.
  @throws IllegalArgumentException If the given value is null or invalid.