Java实现MD5加密以及解密类，附带测试类，具体见代码。

MD5加密解密类——MyMD5Util,代码如下

package com.zyg.security.md5;

import java.io.UnsupportedEncodingException;

import java.security.MessageDigest;

import java.security.NoSuchAlgorithmException;

import java.security.SecureRandom;

import java.util.Arrays;

public class MyMD5Util {

private static final String HEX_NUMS_STR="0123456789ABCDEF";

private static final Integer SALT_LENGTH = 12;

/**

* 将16进制字符串转换成字节数组

* @param hex

* @return

*/

public static byte[] hexStringToByte(String hex) {

int len = (hex.length() / 2);

byte[] result = new byte[len];

char[] hexChars = hex.toCharArray();

for (int i = 0; i < len; i++) {

int pos = i * 2;

result[i] = (byte) (HEX_NUMS_STR.indexOf(hexChars[pos]) << 4

| HEX_NUMS_STR.indexOf(hexChars[pos + 1]));

}

return result;

}

/**

* 将指定byte数组转换成16进制字符串

* @param b

* @return

*/

public static String byteToHexString(byte[] b) {

StringBuffer hexString = new StringBuffer();

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

String hex = Integer.toHexString(b[i] & 0xFF);

if (hex.length() == 1) {

hex = '0' + hex;

}

hexString.append(hex.toUpperCase());

}

return hexString.toString();

}

/**

* 验证口令是否合法

* @param password

* @param passwordInDb

* @return

* @throws NoSuchAlgorithmException

* @throws UnsupportedEncodingException

*/

public static boolean validPassword(String password, String passwordInDb)

throws NoSuchAlgorithmException, UnsupportedEncodingException {

//将16进制字符串格式口令转换成字节数组

byte[] pwdInDb = hexStringToByte(passwordInDb);

//声明盐变量

byte[] salt = new byte[SALT_LENGTH];

//将盐从数据库中保存的口令字节数组中提取出来

System.arraycopy(pwdInDb, 0, salt, 0, SALT_LENGTH);

//创建消息摘要对象

MessageDigest md = MessageDigest.getInstance("MD5");

//将盐数据传入消息摘要对象

md.update(salt);

//将口令的数据传给消息摘要对象

md.update(password.getBytes("UTF-8"));

//生成输入口令的消息摘要

byte[] digest = md.digest();

//声明一个保存数据库中口令消息摘要的变量

byte[] digestInDb = new byte[pwdInDb.length - SALT_LENGTH];

//取得数据库中口令的消息摘要

System.arraycopy(pwdInDb, SALT_LENGTH, digestInDb, 0, digestInDb.length);

//比较根据输入口令生成的消息摘要和数据库中消息摘要是否相同

if (Arrays.equals(digest, digestInDb)) {

//口令正确返回口令匹配消息

return true;

} else {

//口令不正确返回口令不匹配消息

return false;

}

}

/**

* 获得加密后的16进制形式口令

* @param password

* @return

* @throws NoSuchAlgorithmException

* @throws UnsupportedEncodingException

*/

public static String getEncryptedPwd(String password)

throws NoSuchAlgorithmException, UnsupportedEncodingException {

//声明加密后的口令数组变量

byte[] pwd = null;

//随机数生成器

SecureRandom random = new SecureRandom();

//声明盐数组变量

byte[] salt = new byte[SALT_LENGTH];

//将随机数放入盐变量中

random.nextBytes(salt);

//声明消息摘要对象

MessageDigest md = null;

//创建消息摘要

md = MessageDigest.getInstance("MD5");

//将盐数据传入消息摘要对象

md.update(salt);

//将口令的数据传给消息摘要对象

md.update(password.getBytes("UTF-8"));

//获得消息摘要的字节数组

byte[] digest = md.digest();

//因为要在口令的字节数组中存放盐，所以加上盐的字节长度

pwd = new byte[digest.length + SALT_LENGTH];

//将盐的字节拷贝到生成的加密口令字节数组的前12个字节，以便在验证口令时取出盐

System.arraycopy(salt, 0, pwd, 0, SALT_LENGTH);

//将消息摘要拷贝到加密口令字节数组从第13个字节开始的字节

System.arraycopy(digest, 0, pwd, SALT_LENGTH, digest.length);

//将字节数组格式加密后的口令转化为16进制字符串格式的口令

return byteToHexString(pwd);

}

}

测试类——Client,代码如下：

package com.zyg.security.md5;

import java.io.UnsupportedEncodingException;

import java.security.NoSuchAlgorithmException;

import java.util.HashMap;

import java.util.Map;

public class Client {

private static Map users = new HashMap();

public static void main(String[] args){

String userName = "zyg";

String password = "123";

registerUser(userName,password);

userName = "changong";

password = "456";

registerUser(userName,password);

String loginUserId = "zyg";

String pwd = "1232";

try {

if(loginValid(loginUserId,pwd)){

System.out.println("欢迎登陆！！！");

}else{

System.out.println("口令错误，请重新输入！！！");

}

} catch (NoSuchAlgorithmException e) {

// TODO Auto-generated catch block

e.printStackTrace();

} catch (UnsupportedEncodingException e) {

// TODO Auto-generated catch block

e.printStackTrace();

}

}

/**

* 注册用户

*

* @param userName

* @param password

*/

public static void registerUser(String userName,String password){

String encryptedPwd = null;

try {

encryptedPwd = MyMD5Util.getEncryptedPwd(password);

users.put(userName, encryptedPwd);

} catch (NoSuchAlgorithmException e) {

// TODO Auto-generated catch block

e.printStackTrace();

} catch (UnsupportedEncodingException e) {

// TODO Auto-generated catch block

e.printStackTrace();

}

}

/**

* 验证登陆

*

* @param userName

* @param password

* @return

* @throws UnsupportedEncodingException

* @throws NoSuchAlgorithmException

*/

public static boolean loginValid(String userName,String password)

throws NoSuchAlgorithmException, UnsupportedEncodingException{

String pwdInDb = (String)users.get(userName);

if(null!=pwdInDb){ // 该用户存在

return MyMD5Util.validPassword(password, pwdInDb);

}else{

System.out.println("不存在该用户！！！");

return false;

}

}

}