web开发下的各种下载方法

利用TransmitFile方法，解决Response.BinaryWrite下载超过400mb的文件时导致Aspnet_wp.exe进程回收而无法成功下载的问题。 代码如下：

 Response.ContentType = "application/x-zip-compressed";
  Response.AddHeader("Content-Disposition", "attachment;filename=z.zip");
  string filename = Server.MapPath("DownLoad/aaa.zip");
  Response.TransmitFile(filename);

IO的WriteFile实现下载

 string fileName ="aaa.zip";//客户端保存的文件名
  string filePath=Server.MapPath("DownLoad/aaa.zip");//路径

  FileInfo fileInfo = new FileInfo(filePath);
  Response.Clear();
  Response.ClearContent();
  Response.ClearHeaders();
  Response.AddHeader("Content-Disposition", "attachment;filename=" + fileName);
  Response.AddHeader("Content-Length", fileInfo.Length.ToString());
  Response.AddHeader("Content-Transfer-Encoding", "binary");
  Response.ContentType = "application/octet-stream";
  Response.ContentEncoding = System.Text.Encoding.GetEncoding("gb2312");
  Response.WriteFile(fileInfo.FullName);
  Response.Flush();
  Response.End();

WriteFile分块下载

string fileName = "aaa.zip";//客户端保存的文件名
  string filePath = Server.MapPath("DownLoad/aaa.zip");//路径

  System.IO.FileInfo fileInfo = new System.IO.FileInfo(filePath);

  if (fileInfo.Exists == true)
  {
  const long ChunkSize = 102400;//100K 每次读取文件，只读取100Ｋ，这样可以缓解服务器的压力
  byte[] buffer = new byte[ChunkSize];

  Response.Clear();
  System.IO.FileStream iStream = System.IO.File.OpenRead(filePath);
  long dataLengthToRead = iStream.Length;//获取下载的文件总大小
  Response.ContentType = "application/octet-stream";
  Response.AddHeader("Content-Disposition", "attachment; filename=" + HttpUtility.UrlEncode(fileName));
  while (dataLengthToRead > 0 && Response.IsClientConnected) 
  {
  int lengthRead = iStream.Read(buffer, 0, Convert.ToInt32(ChunkSize));//读取的大小
  Response.OutputStream.Write(buffer, 0, lengthRead);
  Response.Flush();
  dataLengthToRead = dataLengthToRead - lengthRead;
  }
  Response.Close();
  }

  //流方式下载

 string fileName = "aaa.zip";//客户端保存的文件名
  string filePath = Server.MapPath("DownLoad/aaa.zip");//路径

  //以字符流的形式下载文件
  FileStream fs = new FileStream(filePath, FileMode.Open);
  byte[] bytes = new byte[(int)fs.Length];
  fs.Read(bytes, 0, bytes.Length);
  fs.Close();
  Response.ContentType = "application/octet-stream";
  //通知浏览器下载文件而不是打开
  Response.AddHeader("Content-Disposition", "attachment; filename=" + HttpUtility.UrlEncode(fileName, System.Text.Encoding.UTF8));
  Response.BinaryWrite(bytes);
  Response.Flush();
  Response.End();

最后一种支持断点下载

/// <summary>
        /// 支持断点续传的下载大文件的函数
        /// </summary>
        /// <param name="downloadFilePath">被下载文件的路径，相对和绝对都可以</param>
        /// <param name="showFileName">显示给用户的文件名，可以为空</param>
        /// <param name="fileType">要下载的文件类型，如果不确定，请留空</param>
        /// <remarks>用于大文件的下载</remarks>
        public static void BigFileDownload(string downloadFilePath, string showFileName, string fileType)
        {
            downloadFilePath = downloadFilePath.Trim();
            if(string.Empty == downloadFilePath)
                ShowErrorMessage("没有指定要下载的文件路径！");
            
            if(downloadFilePath.IndexOf(":") < 0)
                downloadFilePath = System.Web.HttpContext.Current.Server.MapPath(downloadFilePath);

            showFileName = showFileName.Trim();
            if(string.Empty == showFileName)
                showFileName = Path.GetFileName(downloadFilePath);

            showFileName = System.Web.HttpUtility.UrlEncode(System.Web.HttpContext.Current.Request.ContentEncoding.GetBytes(showFileName));
            
            fileType = fileType.Trim();
            if(string.Empty == fileType)
                fileType = "application/octet-stream";

            System.Web.HttpContext.Current.Response.Clear();
            Stream objStream = null;
            byte[] btBuffer = new byte[8192];  // 1024*8 = 8Kb
            int intLength = 0;
            long lngData2Read = 0;
            try
            {
                using(objStream = new FileStream(downloadFilePath, FileMode.Open, FileAccess.Read, FileShare.Read))
                {
                    lngData2Read = objStream.Length;
                    
                    输出HTTP头信息
                    
                    while(lngData2Read > 0)
                    {
                        if(HttpContext.Current.Response.IsClientConnected)
                        {
                            intLength = objStream.Read(btBuffer, 0, 8192);
                            HttpContext.Current.Response.OutputStream.Write(btBuffer, 0, intLength);
                            HttpContext.Current.Response.Flush();
                            lngData2Read -= intLength;
                            btBuffer = new byte[8192];
                        }
                        else
                        {
                            lngData2Read = -1;
                        }
                    }
                }
            }
            catch(Exception ex)
            {
                ShowErrorMessage(ex.Message);
            }
            // 结束文件下载，此句不可缺少，否则会把本页的HTML代码一起下载文件里
            HttpContext.Current.Response.End();
        }

        /// <summary>
        /// 输出错误信息给用户，采用客户端弹出框的方式
        /// </summary>
        /// <param name="errorMessage">错误信息的内容</param>
        internal static void ShowErrorMessage(string errorMessage)
        {
            errorMessage = errorMessage.Replace("'", "\"");
            System.Web.HttpContext.Current.Response.Write("<script language='javascript'>");
            System.Web.HttpContext.Current.Response.Write("alert('");
            System.Web.HttpContext.Current.Response.Write(errorMessage);
            System.Web.HttpContext.Current.Response.Write("');</script>");
            System.Web.HttpContext.Current.Response.End();
        }