Byte Array to hex string and back

bytearray.java

public static String byteArrayToHex(byte[] a) {
        StringBuilder sb = new StringBuilder(a.length * 2);
        for(byte b: a)
            sb.append(String.format("%02x", b));
        return sb.toString();
    }

    public static byte[] hexStringToByteArray(String s) {
        int len = s.length();
        byte[] data = new byte[len/2];

        for(int i = 0; i < len; i+=2){
            data[i/2] = (byte) ((Character.digit(s.charAt(i), 16) << 4) + Character.digit(s.charAt(i+1), 16));
        }

        return data;
    }