Wie konvertiere ich in Java ein Byte-Array in eine Zeichenkette aus Hex-Ziffern, wobei führende Nullen erhalten bleiben?

Question

Ich arbeite mit einigen Beispiel-Java-Code für die Herstellung von md5 Hashes. Ein Teil wandelt die Ergebnisse von Bytes in eine Zeichenkette aus Hex-Ziffern um:

byte messageDigest[] = algorithm.digest();     
StringBuffer hexString = new StringBuffer();
for (int i=0;i<messageDigest.length;i++) {
    hexString.append(Integer.toHexString(0xFF & messageDigest[i]));
    }

Es funktioniert jedoch nicht ganz, da toHexString offenbar führende Nullen abschneidet. Also, was ist der einfachste Weg, um von Byte-Array zu Hex-String, die die führenden Nullen behält gehen?

Answer 1

Ich fand Integer.toHexString ein wenig langsam. Wenn Sie viele Bytes konvertieren, sollten Sie in Erwägung ziehen, ein Array von Strings zu erstellen, das "00" "FF" enthält, und die Ganzzahl als Index zu verwenden. D.h..

hexString.append(hexArray[0xFF & messageDigest[i]]);

Das geht schneller und garantiert die richtige Länge. Benötigt nur das Array von Strings:

String[] hexArray = {
"00","01","02","03","04","05","06","07","08","09","0A","0B","0C","0D","0E","0F",
"10","11","12","13","14","15","16","17","18","19","1A","1B","1C","1D","1E","1F",
"20","21","22","23","24","25","26","27","28","29","2A","2B","2C","2D","2E","2F",
"30","31","32","33","34","35","36","37","38","39","3A","3B","3C","3D","3E","3F",
"40","41","42","43","44","45","46","47","48","49","4A","4B","4C","4D","4E","4F",
"50","51","52","53","54","55","56","57","58","59","5A","5B","5C","5D","5E","5F",
"60","61","62","63","64","65","66","67","68","69","6A","6B","6C","6D","6E","6F",
"70","71","72","73","74","75","76","77","78","79","7A","7B","7C","7D","7E","7F",
"80","81","82","83","84","85","86","87","88","89","8A","8B","8C","8D","8E","8F",
"90","91","92","93","94","95","96","97","98","99","9A","9B","9C","9D","9E","9F",
"A0","A1","A2","A3","A4","A5","A6","A7","A8","A9","AA","AB","AC","AD","AE","AF",
"B0","B1","B2","B3","B4","B5","B6","B7","B8","B9","BA","BB","BC","BD","BE","BF",
"C0","C1","C2","C3","C4","C5","C6","C7","C8","C9","CA","CB","CC","CD","CE","CF",
"D0","D1","D2","D3","D4","D5","D6","D7","D8","D9","DA","DB","DC","DD","DE","DF",
"E0","E1","E2","E3","E4","E5","E6","E7","E8","E9","EA","EB","EC","ED","EE","EF",
"F0","F1","F2","F3","F4","F5","F6","F7","F8","F9","FA","FB","FC","FD","FE","FF"};

Answer 2

Ich habe für die gleiche Sache gesucht ... einige gute Ideen hier, aber ich lief ein paar Mikro-Benchmarks. Ich fand den folgenden als den schnellsten (modifiziert von Ayman's oben und etwa 2x so schnell, und etwa 50% schneller als Steve's direkt über diesem):

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: Ups - ich habe übersehen, dass dies im Wesentlichen dasselbe ist wie das von kgiannakakis und daher eine führende 0 entfernt werden kann. Wenn man dies jedoch wie folgt ändert, ist es immer noch am schnellsten:

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 3

Ich würde so etwas für feste Längen, wie Hashes, verwenden:

md5sum = String.format("%032x", new BigInteger(1, md.digest()));

El 0 in der Maske macht die Polsterung...

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

Guave macht es auch ziemlich einfach:

BaseEncoding.base16().encode( bytes );

Es ist eine gute Alternative, wenn Apache Commons nicht verfügbar ist. Es hat auch einige schöne Kontrollen der Ausgabe wie:

byte[] bytes = new byte[] { 0xa, 0xb, 0xc, 0xd, 0xe, 0xf };
BaseEncoding.base16().lowerCase().withSeparator( ":", 2 ).encode( bytes );
// "0a:0b:0c:0d:0e:0f"