import java.security.MessageDigest;

public class MD5 {

    //公盐

    private static final String PUBLIC_SALT = "demo" ;

    //十六进制下数字到字符的映射数组

    private final static String[] hexDigits = {"0", "1", "2", "3", "4",

        "5", "6", "7", "8", "9", "a", "b", "c", "d", "e", "f"};

    /**

     * 用户密码加密，盐值为 ：私盐+公盐

     * @param  password 密码

     * @param  salt 私盐

     * @return  MD5加密字符串

     */

    public static String encryptPassword(String password,String salt){

        return encodeByMD5(PUBLIC_SALT+password+salt);

    }

    /**

     * md5加密算法

     * @param  originString

     * @return

     */

    private static String encodeByMD5(String originString){

        if (originString != null){

            try{

                //创建具有指定算法名称的信息摘要

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

                //使用指定的字节数组对摘要进行最后更新，然后完成摘要计算

                byte[] results = md.digest(originString.getBytes());

                //将得到的字节数组变成字符串返回

                String resultString = byteArrayToHexString(results);

                return resultString.toUpperCase();

            } catch(Exception ex){

                ex.printStackTrace();

            }

        }

        return null;

    } 

    /**

     * 转换字节数组为十六进制字符串

     * @param     字节数组

     * @return    十六进制字符串

     */

    private 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();

    }  

    /** 将一个字节转化成十六进制形式的字符串     */

    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];

    }

}