In Java, how do I convert a byte array to a string of hex digits while keeping leading zeros? [duplicate]

Answer 1

I've been looking for the same thing ... some good ideas here, but I ran a few micro benchmarks. I found the following to be the fastest (modified from Ayman's above and about 2x as fast, and about 50% faster than Steve's just above this one):

public static String hash(String text, String algorithm)
        throws NoSuchAlgorithmException {
    byte[] hash = MessageDigest.getInstance(algorithm).digest(text.getBytes());
    return new BigInteger(1, hash).toString(16);
}

Edit: Oops - missed that this is essentially the same as kgiannakakis's and so may strip off a leading 0. Still, modifying this to the following, it's still the fastest:

public static String hash(String text, String algorithm)
        throws NoSuchAlgorithmException {
    byte[] hash = MessageDigest.getInstance(algorithm).digest(text.getBytes());
    BigInteger bi = new BigInteger(1, hash);
    String result = bi.toString(16);
    if (result.length() % 2 != 0) {
        return "0" + result;
    }
    return result;
}

Answer 2

And how can you convert back again from ascii to byte array ?

i followed following code to convert to ascii given by Jemenake.

public static String toHexString(byte[] bytes) {
    char[] hexArray = {'0','1','2','3','4','5','6','7','8','9','A','B','C','D','E','F'};
    char[] hexChars = new char[bytes.length * 2];
    int v;
    for ( int j = 0; j < bytes.length; j++ ) {
        v = bytes[j] & 0xFF;
        hexChars[j*2] = hexArray[v/16];
        hexChars[j*2 + 1] = hexArray[v%16];
    }
    return new String(hexChars);
}

Answer 3

I'm surprised that no one came up with the following solution:

StringWriter sw = new StringWriter();
com.sun.corba.se.impl.orbutil.HexOutputStream hex = new com.sun.corba.se.impl.orbutil.HexOutputStream(sw);
hex.write(byteArray);
System.out.println(sw.toString());

Answer 4

static String toHex(byte[] digest) {
    StringBuilder sb = new StringBuilder();
    for (byte b : digest) {
        sb.append(String.format("%1$02X", b));
    }

    return sb.toString();
}

Answer 5

String result = String.format("%0" + messageDigest.length + "s", hexString.toString())

That's the shortest solution given what you already have. If you could convert the byte array to a numeric value, String.format can convert it to a hex string at the same time.

Answer 6

You can get it writing less without external libraries:

String hex = (new HexBinaryAdapter()).marshal(md5.digest(YOUR_STRING.getBytes()))