Scala one-liner to generate MD5 Hash from string

Question

I'm new to Scala and I found this interesting one-liner to generate a hex-encoded MD5 hash from a string. I was hoping someone could help me understand this better.

private def getMd5(inputStr: String): String = {
  val md: MessageDigest = MessageDigest.getInstance("MD5")
  md.digest(inputStr.getBytes()).map(0xFF & _).map { "%02x".format(_) }.foldLeft("") {_ + _}
}

Thanks.

Answer 1

It's just a analogue to this java code but without StringBuilder (it's up to you)

    MessageDigest messageDigest = MessageDigest.getInstance("SHA-512");
    String password = "secret";
    messageDigest.update(password.getBytes());
    byte[] bytes = messageDigest.digest();
    StringBuilder stringBuilder = new StringBuilder();
    for (byte aByte : bytes) {
        stringBuilder.append(Integer.toString((aByte & 0xff) + 0x100, 16).substring(1));
    }
    System.out.println(stringBuilder.toString());

Let's consider second line:

md.digest(inputStr.getBytes()).map(0xFF & _).map { "%02x".format(_) }.foldLeft("") {_ + _}

1. md.digest(inputStr.getBytes()) ---- take bytes from String
2. md.digest(inputStr.getBytes()).map(0xFF & _) --- bitwise & with every item of array (map return a new array)
3. md.digest(inputStr.getBytes()).map(0xFF & ).map { "%02x".format() } map with formatting each item.
4. md.digest(inputStr.getBytes()).map(0xFF & ).map { "%02x".format() }.foldLeft("") {_ + _} it's typical fold, in our case starting from left and init value "", (if it will be easier for you, it's "far" analogue of StringBuilder behaving in above example). I recommend you to read about fold, reduce and etc. actions in scala. e.g. https://coderwall.com/p/4l73-a/scala-fold-foldleft-and-foldright