public static class FileHelper 
    { 
        /// <summary> 
        /// 获取文件MD5值 
        /// </summary> 
        /// <param name="fileName">文件绝对路径</param> 
        /// <returns>MD5值</returns> 
        public static string GetFileMD5(string fileName) 
        { 
            try 
            { 
                using (System.IO.FileStream fs = new System.IO.FileStream(fileName, System.IO.FileMode.Open, System.IO.FileAccess.Read)) 
                { 
                    return GetFileMD5(fs); 
                } 
            } 
            catch (Exception ex) 
            { 
                throw new Exception("GetMD5HashFromFile() fail,error:" + ex.Message); 
            } 
        } 
 
        /// <summary> 
        /// 获取文件MD5值 
        /// </summary> 
        /// <param name="fs">文件流</param> 
        /// <returns>MD5值</returns> 
        public static string GetFileMD5(FileStream fs) 
        { 
            try 
            { 
                System.Security.Cryptography.MD5 md5 = new System.Security.Cryptography.MD5CryptoServiceProvider(); 
                byte[] retVal = md5.ComputeHash(fs); 
 
                StringBuilder sb = new StringBuilder(); 
                for (int i = 0; i < retVal.Length; i++) 
                { 
                    sb.Append(retVal[i].ToString("x2")); 
                } 
                return sb.ToString(); 
            } 
            catch (Exception ex) 
            { 
                throw new Exception("生成文件MD5是发生异常:" + ex.Message); 
            } 
        } 
    }