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;
/**
*
Title:
*
Description:
*
Copyright: Copyright (c) 2003
*
Company:
* @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));
}
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

程序有错，

应该改为，

 public static String byteArrayToHexString(byte[] b) {

           StringBuffer resultSb = new StringBuffer();

            for (int i = 0; i < b.length; i++) {

                resultSb.append(byteToHexString(b));

           }

             return resultSb.toString();

         }

 

resultSb.append(byteToHexString(b[ i ]));

[ 本帖最后由 bushilengmod1b68293 于 2008-10-7 16:50 编辑 ]