在 Java 中，如何在保留前导零的同时将字节数组转换为十六进制数字字符串？
声明：本页面是StackOverFlow热门问题的中英对照翻译，遵循CC BY-SA 4.0协议，如果您需要使用它，必须同样遵循CC BY-SA许可，注明原文地址和作者信息，同时你必须将它归于原作者（不是我）：StackOverFlow
原文地址: http://stackoverflow.com/questions/332079/
Warning: these are provided under cc-by-sa 4.0 license. You are free to use/share it, But you must attribute it to the original authors (not me):
StackOverFlow
In Java, how do I convert a byte array to a string of hex digits while keeping leading zeros?
提问by Eugene M
I'm working with some example java code for making md5 hashes. One part converts the results from bytes to a string of hex digits:
我正在使用一些示例 java 代码来制作 md5 哈希。一部分将结果从字节转换为一串十六进制数字：
byte messageDigest[] = algorithm.digest();
StringBuffer hexString = new StringBuffer();
for (int i=0;i<messageDigest.length;i++) {
hexString.append(Integer.toHexString(0xFF & messageDigest[i]));
}
However, it doesn't quite work since toHexString apparently drops off leading zeros. So, what's the simplest way to go from byte array to hex string that maintains the leading zeros?
但是，由于 toHexString 显然去掉了前导零，所以它并不完全有效。那么，从字节数组到保持前导零的十六进制字符串的最简单方法是什么？
采纳答案by Michael Myers
A simple approach would be to check how many digits are output by Integer.toHexString()and add a leading zero to each byte if needed. Something like this:
一个简单的方法是检查输出了多少位数字，Integer.toHexString()并在需要时为每个字节添加一个前导零。像这样的东西：
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();
}
回答by kgiannakakis
This what I am using for MD5 hashes:
这是我用于 MD5 哈希的内容：
public static String getMD5(String filename)
throws NoSuchAlgorithmException, IOException {
MessageDigest messageDigest =
java.security.MessageDigest.getInstance("MD5");
InputStream in = new FileInputStream(filename);
byte [] buffer = new byte[8192];
int len = in.read(buffer, 0, buffer.length);
while (len > 0) {
messageDigest.update(buffer, 0, len);
len = in.read(buffer, 0, buffer.length);
}
in.close();
return new BigInteger(1, messageDigest.digest()).toString(16);
}
EDIT: I've tested and I've noticed that with this also trailing zeros are cut. But this can only happen in the beginning, so you can compare with the expected length and pad accordingly.
编辑：我已经测试过，并且我注意到这也减少了尾随零。但这只能在开始时发生，因此您可以与预期长度进行比较并相应地填充。
回答by Ed Marty
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.formatcan convert it to a hex string at the same time.
鉴于您已经拥有的，这是最短的解决方案。如果可以将字节数组转换为数值，则String.format可以同时将其转换为十六进制字符串。
回答by Fernando Miguélez
byte messageDigest[] = algorithm.digest();
StringBuffer hexString = new StringBuffer();
for (int i = 0; i < messageDigest.length; i++) {
String hexByte = Integer.toHexString(0xFF & messageDigest[i]);
int numDigits = 2 - hexByte.length();
while (numDigits-- > 0) {
hexString.append('0');
}
hexString.append(hexByte);
}
回答by Brandon DuRette
Check out Hex.encodeHexStringfrom Apache Commons Codec.
查看来自Apache Commons Codec 的Hex.encodeHexString。
import org.apache.commons.codec.binary.Hex;
String hex = Hex.encodeHexString(bytes);
回答by agentbillo
This solution is a little older school, and should be memory efficient.
这个解决方案有点旧，应该是内存高效的。
public static String toHexString(byte bytes[]) {
if (bytes == null) {
return null;
}
StringBuffer sb = new StringBuffer();
for (int iter = 0; iter < bytes.length; iter++) {
byte high = (byte) ( (bytes[iter] & 0xf0) >> 4);
byte low = (byte) (bytes[iter] & 0x0f);
sb.append(nibble2char(high));
sb.append(nibble2char(low));
}
return sb.toString();
}
private static char nibble2char(byte b) {
byte nibble = (byte) (b & 0x0f);
if (nibble < 10) {
return (char) ('0' + nibble);
}
return (char) ('a' + nibble - 10);
}
回答by Ayman
You can use the one below. I tested this with leading zero bytes and with initial negative bytes as well
您可以使用下面的一种。我用前导零字节和初始负字节对此进行了测试
public static String toHex(byte[] bytes) {
BigInteger bi = new BigInteger(1, bytes);
return String.format("%0" + (bytes.length << 1) + "X", bi);
}
If you want lowercase hex digits, use "x"in the format String.
如果您想要小写的十六进制数字，请使用"x"字符串格式。
回答by Peter Lawrey
Another option
另外一个选项
public static String toHexString(byte[]bytes) {
StringBuilder sb = new StringBuilder(bytes.length*2);
for(byte b: bytes)
sb.append(Integer.toHexString(b+0x800).substring(1));
return sb.toString();
}
回答by Peter Lawrey
I found Integer.toHexString to be a little slow. If you are converting many bytes, you may want to consider building an array of Strings containing "00".."FF" and use the integer as the index. I.e.
我发现 Integer.toHexString 有点慢。如果您要转换很多字节，您可能需要考虑构建一个包含“00”..“FF”的字符串数组并使用整数作为索引。IE
hexString.append(hexArray[0xFF & messageDigest[i]]);
This is faster and ensures the correct length. Just requires the array of strings:
这更快并确保正确的长度。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"};
回答by Peter Lawrey
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):
我一直在寻找同样的东西......这里有一些好主意，但我运行了一些微基准测试。我发现以下是最快的（从上面的 Ayman 修改而来，速度大约是其 2 倍，比 Steve 的速度快 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);
}
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:
编辑：糟糕 - 错过了这与 kgiannakakis 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，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;
}
