rafraf rafraf - 1 month ago 6
Java Question

Convert a string representation of a hex dump to a byte array using Java?

I am looking for a way to convert a long string (from a dump), that represents hex values into a byte array.

I couldn't have phrased it better than the person that posted the same question here:

http://www.experts-exchange.com/Programming/Programming_Languages/Java/Q_21062554.html

But to keep it original, I'll phrase it my own way: suppose I have a string "00A0BF" that I would like interpreted as the byte[] {0x00,0xA0,0xBf} what should I do?

I am a Java novice and ended up using BigInteger and watching out for leading hex zeros. But I think it is ugly and I am sure I am missing something simple...

Answer

Here's a solution that I think is better than any posted so far:

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;
}

Reasons why it is an improvement:

  • Safe with leading zeros (unlike BigInteger) and with negative byte values (unlike Byte.parseByte)

  • Doesn't convert the String into a char[], or create StringBuilder and String objects for every single byte.

Feel free to add argument checking via assert or exceptions if the argument is not known to be safe.

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