MD5

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：

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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;   
        }   
    }   
}