package com.drawthink.platform.util;

import java.security.MessageDigest;

import java.security.NoSuchAlgorithmException;

/**

 * MD5类:加密

 */

public class MD5Util {

    //获取字符串的MD5串

    public static String Md5(//

            String plainText //原字符串

    ) {

        if (plainText == null) {

            return null;

        }

        StringBuffer buf = new StringBuffer();

        try {

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

            md.update(plainText.getBytes());

            md.reset();

            byte b[] = md.digest();

            int i;

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

                i = b[offset];

                if (i < ) {

                    i += ;

                }

                if (i < ) {

                    buf.append("");

                }

                buf.append(Integer.toHexString(i));

            }

        } catch (NoSuchAlgorithmException ex) {

            ex.printStackTrace();

        }

        return buf.toString();

    }

}

-------------------解密---------------------------
package com.drawthink.platform.util;

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 = ;

    /**

    * 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() / );

        byte[] result = new byte[len];

        char[] hexChars = hex.toCharArray();

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

            int pos = i * ;

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

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

        }

        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 = ; i < b.length; i++) {

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

             if (hex.length() == ) {

                 hex = '' + 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, , salt, , 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, , 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, , pwd, , 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, , 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);

     }

     //测试方法

     public static void main(String[] args) {

        try {

            String password = "5a105e8b9d40e1329780d62ea2265d8a";

            boolean encryptedPwd = MyMD5Util.validPassword(password,password);

            System.out.println(encryptedPwd);

        } catch (NoSuchAlgorithmException | UnsupportedEncodingException e) {

            // TODO Auto-generated catch block

            e.printStackTrace();

        }

    }

}