code: public static String convertToBase64Encoding(String hexEncodedChecksum) {
          byte[] checksumBytes = hexStringToByteArray(hexEncodedChecksum);
          return new String(Base64.encodeBase64(checksumBytes));
      }
docs: Converts a hex-encoded checksum (like that produced by the getChecksum
  and generateChecksum methods of this class) to a base64-encoded checksum
  
  @param hexEncodedChecksum hex-encoded checksum
  @return base64-encoded checksum