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];        }  }