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由于消息摘要唯一性和不可逆性的特点，所以不失为一种简单的常用的加密手段，比如你可以用md5来加密你的应用中的用户口令。
package test;
import java.security.messagedigest;
/**
* <p>title: </p>
* <p>description: </p>
* <p>copyright: copyright (c) 2003</p>
* <p>company: </p>
* @author unascribed
* @version 1.0
*/
public class stringutil {
private final static string[] hexdigits = {
"0", "1", "2", "3", "4", "5", "6", "7",
"8", "9", "a", "b", "c", "d", "e", "f"};
/**
* 转换字节数组为16进制字串
* @param b 字节数组
* @return 16进制字串
*/
public static string bytearraytohexstring(byte[] b) {
stringbuffer resultsb = new stringbuffer();
for (int i = 0; i < b.length; i++) {
resultsb.append(bytetohexstring(b[i]));
}
return resultsb.tostring();
}
private static string bytetohexstring(byte b) {
int n = b;
if (n < 0)
n = 256 + n;
int d1 = n / 16;
int d2 = n % 16;
return hexdigits[d1] + hexdigits[d2];
}
public static string md5encode(string origin) {
string resultstring = null;
try {
resultstring=new string(origin);
messagedigest md = messagedigest.getinstance("md5");
resultstring=bytearraytohexstring(md.digest(resultstring.getbytes()));
}
catch (exception ex) {
}
return resultstring;
}
public static void main(string[] args){
system.err.println(md5encode("a"));
}
}
在rfc 1321中，给出了test suite用来检验你的实现是否正确：
md5 ("") = d41d8cd98f00b204e9800998ecf8427e
md5 ("a") = 0cc175b9c0f1b6a831c399e269772661
md5 ("abc") = 900150983cd24fb0d6963f7d28e17f72
md5 ("message digest") = f96b697d7cb7938d525a2f31aaf161d0
md5 ("abcdefghijklmnopqrstuvwxyz") = c3fcd3d76192e4007dfb496cca67e13b
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