我正在使用一些用于生成MD5哈希的Java示例代码。其中一部分将结果从字节转换为十六进制数字字符串：
byte messageDigest[] = algorithm.digest();
StringBuffer hexString = new StringBuffer();
for (int i=0;i<messageDigest.length;i++) {
hexString.append(Integer.toHexString(0xFF & messageDigest[i]));
}
然而，这种方法并不完全有效，因为 toHexString 显然会删除前导零。那么，从字节数组转换为十六进制字符串并保留前导零的最简单方法是什么？
请查看来自Apache Commons Codec的Hex.encodeHexString。
import org.apache.commons.codec.binary.Hex;
String hex = Hex.encodeHexString(bytes);
您可以使用下面这个。我测试过包含前导零字节和初始负字节的情况。
public static String toHex(byte[] bytes) {
BigInteger bi = new BigInteger(1, bytes);
return String.format("%0" + (bytes.length << 1) + "X", bi);
}
"x"。f"${BigInt(1, myIpv6ByteArray)}%032x"。 - Mark Rajcok一个简单的方法是检查 Integer.toHexString() 输出了多少个数字，如果需要，为每个字节添加前导零。像这样：
一个简单的方法是检查 Integer.toHexString() 输出了多少个数字，如果需要，为每个字节添加前导零。像这样：
public static String toHexString(byte[] bytes) {
StringBuilder hexString = new StringBuilder();
for (int i = 0; i < bytes.length; i++) {
String hex = Integer.toHexString(0xFF & bytes[i]);
if (hex.length() == 1) {
hexString.append('0');
}
hexString.append(hex);
}
return hexString.toString();
}
hexString之前先附加了一个0。 - Michael MyersInteger.toHexString((byte)0xff) 时，它返回了 "ffffffff"，这是由于符号扩展造成的。因此，可能需要取返回字符串的最后两个字符。 - Marvo{0,1,2,3}，它应该返回 0123，但实际上它会返回 00010203，这是哈希的期望结果吗？ - Juzer Ali方法 javax.xml.bind.DatatypeConverter.printHexBinary() 是 Java Architecture for XML Binding (JAXB) 的一部分，它是将 byte[] 转换为十六进制字符串的便捷方式。DatatypeConverter 类还包括许多其他有用的数据操作方法。
javax.xml.bind不存在，如果您想使用包含DatatypeConverter的JAXB，则需要从Maven安装JAXB API和JAXB Runtime。
示例用法：
byte bytes[] = {(byte)0, (byte)0, (byte)134, (byte)0, (byte)61};
String hex = javax.xml.bind.DatatypeConverter.printHexBinary(bytes);
000086003D
DatatypeConverter.parseHexBinary(hexString)。 - Sanghyun Leejava.xml包不再是JDK的一部分。 - AndreasB我喜欢 Steve 的提交，但他本可以少些几个变量，在此过程中节省几行代码。
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);
}
我喜欢这个方法的原因是可以清楚地看到它在做什么（而不是依赖某种神奇的BigInteger黑盒转换），而且你无需担心像前导零之类的边界情况。该程序将每个4位半字节转换为一个十六进制字符，并使用表查找，因此它可能很快速。如果你使用按位移位和AND来替换v/16和v%16，它可能会更快，但是我现在太懒了，没有测试。
public static byte[] bytesFromHex(String hexString) {
final char[] hexArray = {'0', '1', '2', '3', '4', '5', '6', '7', '8', '9', 'A', 'B', 'C', 'D', 'E', 'F'};
char[] hexChars = hexString.toCharArray();
byte[] result = new byte[hexChars.length / 2];
for (int j = 0; j < hexChars.length; j += 2) {
result[j / 2] = (byte) (Arrays.binarySearch(hexArray, hexChars[j]) * 16
+ Arrays.binarySearch(hexArray, hexChars[j + 1]));
}
return result;
} - cn1h我发现 Integer.toHexString 有点慢。如果你要转换很多字节，你可以考虑构建一个包含“00”..“FF”的字符串数组，并使用整数作为索引。
hexString.append(hexArray[0xFF & messageDigest[i]]);
这样做更快，而且可以确保正确的长度。只需要字符串数组：
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"};
对于固定长度的内容，比如哈希值，我会使用类似这样的方法：
md5sum = String.format("%032x", new BigInteger(1, md.digest()));
掩码中的0表示填充...
我一直在寻找同样的东西...这里有一些好的想法，但我进行了一些微型基准测试。我发现以下修改后的代码是最快的（从Ayman的代码修改而来，速度大约是原来的两倍，并且比Steve的代码快了约50%）：
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);
}
编辑：糟糕 - 没有注意到这与kgiannakakis的基本相同，因此可能会去掉前导0。不过，将其修改为以下内容后，它仍然是最快的：
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;
}
{0, 0, 0, 0}，使用 BigInteger 的 toString 方法会返回 "0"。这段代码在其前面添加了另一个 "0" 并返回了 "00"，但结果应该是 "00000000"。 - Daniel Lubarovstatic String toHex(byte[] digest) {
StringBuilder sb = new StringBuilder();
for (byte b : digest) {
sb.append(String.format("%1$02X", b));
}
return sb.toString();
}
StringBuilder 的默认初始容量为16个字符。MD5哈希由32个字符组成。在添加了前16个字符后，内部数组将被复制到一个长度为34的新数组中。此外，每个摘要字节都会创建一个新的 Formatter 实例。默认情况下，每个 Formatter 都会实例化一个新的 StringBuilder 来缓冲其输出。我认为更容易的方法是创建一个只有32个字符初始容量的 StringBuffer (new Formatter(new StringBuilder(32))) ，然后使用它的 format 和 toString 方法。 - RobertBaseEncoding.base16().encode( bytes );
当Apache Commons不可用时，它是一个不错的替代品。它还有一些很好的输出控制，比如:
byte[] bytes = new byte[] { 0xa, 0xb, 0xc, 0xd, 0xe, 0xf };
BaseEncoding.base16().lowerCase().withSeparator( ":", 2 ).encode( bytes );
// "0a:0b:0c:0d:0e:0f"