class CommonHelper    {        /// <summary>        /// 通过字符串获取MD5值，返回32位字符串。        /// </summary>        /// <param name="str"></param>        /// <returns></returns>        public static string GetMD5String(string str)        {            MD5 md5 = MD5.Create();            byte[] data =http://www.mamicode.com/ Encoding.UTF8.GetBytes(str);            byte[] data2 = md5.ComputeHash(data);                        return GetbyteToString(data2);            //return BitConverter.ToString(data2).Replace("-", "").ToLower();        }        /// <summary>        /// 获取MD5值。HashAlgorithm.Create("MD5") 或 MD5.Create() HashAlgorithm.Create("SHA256") 或 SHA256.Create()        /// </summary>        /// <param name="str"></param>        /// <param name="hash"></param>        /// <returns></returns>        public static string GetMD5String(string str, HashAlgorithm hash)        {            byte[] data =http://www.mamicode.com/ Encoding.UTF8.GetBytes(str);            byte[] data2 = hash.ComputeHash(data);            return GetbyteToString(data2);            //return BitConverter.ToString(data2).Replace("-", "").ToLower();        }        public static string GetMD5FromFile(string path)        {            MD5 md5 = MD5.Create();            if (!File.Exists(path))            {                return "";            }            FileStream stream = File.OpenRead(path);            byte[] data2 = md5.ComputeHash(stream);            return GetbyteToString(data2);            //return BitConverter.ToString(data2).Replace("-", "").ToLower();        }        private static string GetbyteToString(byte[] data)        {            StringBuilder sb = new StringBuilder();            for (int i = 0; i < data.Length; i++)            {                sb.Append(data[i].ToString("x2"));            }            return sb.ToString();        }    }