Friday, November 30, 2012

Converting a Hex String to a Byte Array in Scala

Here's a Scala method that converts a hex string to an array of bytes. This is useful when needing to encrypt a hex string, because most of the crypto libraries operate on byte arrays.

def hexStringToByteArray(s : String) = {
    val len = s.length();
    var data = new Array[Byte](len / 2)
    var i = 0

    while (i < len) {
        val b = (Character.digit(s.charAt(i), 16) << 4) +
                (Character.digit(s.charAt(i+1), 16))

        data(i / 2) = b.asInstanceOf[Byte]




  1. Asserted hex strings always have an even length, the conversion could be written without mutable data:

    def hexStringToByteArray(s: String) = s.grouped(2).map(cc => (Character.digit(cc(0),16) << 4 | Character.digit(cc(1),16)).toByte).toArray

    I assume, there are many things which can be improved. It depends on the context and the restrictions where the method is to be used.
    Kind regards JP

  2. An eternity late... How about this?

    // Group the string into hex pairs, parse hex values into integer, convert integer to byte.
    s.grouped(2).toArray map { Integer.parseInt(_, 16).toByte }