java BigInteger.toString 方法正在删除前导 0
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BigInteger.toString method is deleting leading 0
提问by Dheeraj Joshi
I am trying to generate MD5 sum using MessageDigest. And i am having following code.
我正在尝试使用 MessageDigest 生成 MD5 总和。我有以下代码。
byte[] md5sum = digest.digest();
BigInteger bigInt = new BigInteger(1, md5sum);
output = bigInt.toString(16);
This returns not 32 character string but a 31 character string 8611c0b0832bce5a19ceee626a403a7
这返回的不是 32 个字符的字符串，而是一个 31 个字符的字符串 8611c0b0832bce5a19ceee626a403a7
Expected String is 08611c0b0832bce5a19ceee626a403a7
预期字符串是 08611c0b0832bce5a19ceee626a403a7
Leading 0 is missing in the output.
输出中缺少前导 0。
I tried the other method
我尝试了另一种方法
byte[] md5sum = digest.digest();
output = new String(Hex.encodeHex(md5sum));
And the output is as expected.
并且输出符合预期。
I checked the doc and Integer.toString does the conversion according to it
我检查了文档，Integer.toString 根据它进行了转换
The digit-to-character mapping provided by Character.forDigit is used, and a minus sign is prepended if appropriate.
使用 Character.forDigit 提供的数字到字符映射，并在适当的情况下添加减号。
and in Character.forDigit methos
并在 Character.forDigit 方法中
The digit argument is valid if 0 <=digit < radix.
如果 0 <=digit < radix，则 digit 参数有效。
Can some one tell me how two methods are different and why leading 0 is deleted?
有人可以告诉我两种方法有何不同以及为什么删除前导 0 吗？
采纳答案by Jon Skeet
I would personally avoidusing BigIntegerto convert binary data to text. That's not really what it's there for, even if it canbe used for that. There's loads of code available to convert a byte[]to its hex representation - e.g. using Apache Commons Codecor a simple single method:
我个人会避免使用BigInteger将二进制数据转换为文本。这并不是它的真正用途，即使它可以用于那个。有大量代码可用于将 a 转换byte[]为其十六进制表示 - 例如使用Apache Commons Codec或简单的单一方法：
private static final char[] HEX_DIGITS = "0123456789ABCDEF".toCharArray();
public static String toHex(byte[] data) {
char[] chars = new char[data.length * 2];
for (int i = 0; i < data.length; i++) {
chars[i * 2] = HEX_DIGITS[(data[i] >> 4) & 0xf];
chars[i * 2 + 1] = HEX_DIGITS[data[i] & 0xf];
}
return new String(chars);
}
回答by Gorets
String.format("%064X", new BigInteger(1, hmac.doFinal(message.getBytes())));
String.format("%064X", new BigInteger(1, hmac.doFinal(message.getBytes())));
where
在哪里
- 0 - zero leading sign
- 64 - string length
- X - Uppercase
- 0 - 零前导符号
- 64 - 字符串长度
- X - 大写
回答by paxdiablo
It's deleted because the leading zero is not significant, according to BigInteger. There is no difference between 27and 000000000027.
根据 ，它被删除是因为前导零不重要BigInteger。27和之间没有区别000000000027。
If you want a specific length, you'll have to force it yourself, with something like:
如果你想要一个特定的长度，你必须自己强迫它，比如：
output = ("00000000000000000000000000000000"+output).substring(output.length());
(kludgy though that is).
（虽然很笨拙）。
回答by user1689394
The deleted zero is replaced using this code:
使用以下代码替换已删除的零：
MessageDigest digest = MessageDigest.getInstance("MD5");
digest.reset();
digest.update(output.getBytes());
byte[] outDigest = digest.digest();
BigInteger outBigInt = new BigInteger(1,outDigest);
output = outBigInt.toString(16);
while (output.length() < 32){
output = "0"+output;
}
loop will account for as many leading zeros as needed
循环将根据需要考虑尽可能多的前导零
回答by Aram
MessageDigest m=MessageDigest.getInstance("MD5");
m.update(PlainText.getBytes(),0,PlainText.length());
String M1=new BigInteger(1,m.digest()).toString(16);
return M1;
