Google Hashing Transformation flow.

hashing.java

// Testing main method.
public static void main(String[] args) throws Exception {
  String firstID = "491d69e08dbdaeacbed17194761f97b1b9c9a3928e7c3b1b0add760a37a45b4d";
  String salt = "DPK54AN4HZE4N9G0D4RC2EOH8A58H1Z6";

  String answer = "71e10f9d4ab22a8c0a31ec27c8913a13a12a5ebb6500baaaea9a9bd694447cc1";

  // Only do second transformation
  // 1. Hex decode |firstID|.
  // 3. Prefix |salt| to |base|.
  // 4. SHA256 hash.
  // 5. Return hex encoded hash.
  byte[] base = Hex.decodeHex(firstID.toCharArray()); // hex decode
  HashTransformation secondTransform = new HashTransformation(HashTransformation.Type.SHA256,
      salt, true);
  // Prefix, hash, and hex encode.
  System.out.println(secondTransform.transform(new String(base))); 
  // This gives 73165e3e19523ea84ffdc2b338248f0c7c5d47f672703f4cb7885537b9a4f559.
}

// Parts of the HashTransformation class.
public HashTransformation(Type type, byte[] salt, boolean hexEncode) {
  this.type = type;
  this.salt = salt;
  this.hexEncode = hexEncode;
}

@Override
public String transform(String value) {
  byte[] hashedBytes;
  switch (type) {
    case MD5:
      hashedBytes = DigestUtils.md5(prefixSalt(value));
      break;
    case SHA1:
      hashedBytes = DigestUtils.sha(prefixSalt(value));
      break;
    case SHA256:
      hashedBytes = DigestUtils.sha256(prefixSalt(value));
      break;
    default:
      throw new NotImplementedException("Unsupported hash " + type);
  }
  return hexEncode ? Hex.encodeHexString(hashedBytes) : Strings.fromBytes(hashedBytes);
}

private byte[] prefixSalt(String value) {
  return Bytes.concat(salt, Strings.toBytes(value));
}