下面是一个将字节转换为十六进制的简单函数

   private static String convertToHex(byte[] data) {
    StringBuffer buf = new StringBuffer();
    for (int i = 0; i < data.length; i++) {
        int halfbyte = (data[i] >>> 4) & 0x0F;
        int two_halfs = 0;
        do {
            if ((0 <= halfbyte) && (halfbyte <= 9))
                buf.append((char) ('0' + halfbyte));
            else
                buf.append((char) ('a' + (halfbyte - 10)));
            halfbyte = data[i] & 0x0F;
        } while(two_halfs++ < 1);
    }
    return buf.toString();
}

如果您乐于使用外部库，则org.apache.commons.codec.binary.Hex类有一个encodeHex方法，该方法接受一个字节[]并返回一个char[]。这个方法比format选项快得多，并且封装了转换的细节。还附带了一个decodeHex方法，用于相反的转换。

下面是一个将字节转换为十六进制的简单函数

   private static String convertToHex(byte[] data) {
    StringBuffer buf = new StringBuffer();
    for (int i = 0; i < data.length; i++) {
        int halfbyte = (data[i] >>> 4) & 0x0F;
        int two_halfs = 0;
        do {
            if ((0 <= halfbyte) && (halfbyte <= 9))
                buf.append((char) ('0' + halfbyte));
            else
                buf.append((char) ('a' + (halfbyte - 10)));
            halfbyte = data[i] & 0x0F;
        } while(two_halfs++ < 1);
    }
    return buf.toString();
}

如果你喜欢流，这里有一个格式-连接方法的单表达式版本:

String hex = IntStream.range(0, bytes.length)
                      .map(i -> bytes[i] & 0xff)
                      .mapToObj(b -> String.format("%02x", b))
                      .collect(Collectors.joining());

遗憾的是没有类似Arrays::streamUnsignedBytes这样的方法。

这是你的快速方法:

    private static final String[] hexes = new String[]{
        "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"
    };

    public static String byteToHex(byte b) {
        return hexes[b&0xFF];
    }

Java 17:引入Java .util. hexformat

Java 17提供了一个实用程序，可以将字节数组和数字转换为对应的十六进制数。假设我们有一个“Hello World”的MD5摘要作为一个字节数组:

var md5 = MessageDigest.getInstance("md5");
md5.update("Hello world".getBytes(UTF_8));

var digest = md5.digest();

现在我们可以使用HexFormat.of().formatHex(byte[])方法将给定的byte[]转换为它的十六进制形式:

jshell> HexFormat.of().formatHex(digest)
$7 ==> "3e25960a79dbc69b674cd4ec67a72c62"

withUpperCase()方法返回前面输出的大写版本:

jshell> HexFormat.of().withUpperCase().formatHex(digest)
$8 ==> "3E25960A79DBC69B674CD4EC67A72C62"