import java.security.MessageDigest;

/**
 * Created by wzf on 2018/9/25.
 */
public class MD5 {

    //公鹽
    private static final String PUBLIC_SALT = "142857" ;
    //十六進位制下數字到字元的對映陣列
    private final static String[] hexDigits = {"0", "1", "2", "3", "4", "5", "6", "7", "8", "9", "a", "b", "c", "d", "e", "f"};

    /**
     * 使用者密碼加密，鹽值為 ：私鹽+公鹽
     * @param  password 密碼
     * @param  salt 私鹽
     * @return  MD5加密字串
     */
    public static String encryptPassword(String password, String salt){
        return encodeByMD5(PUBLIC_SALT+password+salt);
    }

    /**
     * md5加密演算法
     * @param  originString
     * @return
     */
    public static String encodeByMD5(String originString){
        if (originString != null){
            try{
                //建立具有指定演算法名稱的資訊摘要
                MessageDigest md = MessageDigest.getInstance("MD5");
                //使用指定的位元組陣列對摘要進行最後更新，然後完成摘要計算
                byte[] results = md.digest(originString.getBytes());
                //將得到的位元組陣列變成字串返回
                String resultString = byteArrayToHexString(results);
                return resultString.toUpperCase();
            } catch(Exception ex){
                ex.printStackTrace();
            }
        }
        return null;
    }

    /**
     * 轉換位元組陣列為十六進位制字串
     * @return    十六進位制字串
     */
    public static String byteArrayToHexString(byte[] b){
        StringBuffer resultSb = new StringBuffer();
        for (int i = 0; i < b.length; i++){
            resultSb.append(byteToHexString(b[i]));
        }
        return resultSb.toString();
    }

    /** 將一個位元組轉化成十六進位制形式的字串 */
    public 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];
    }
}