sender, EventArgs e)
     {
        /*
          微软为Response对象提供了一个新的方法TransmitFile来解决使用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);
     }

    //WriteFile实现下载
    protected void Button2_Click(object sender, EventArgs e)
     {
        /*
          using System.IO;
         
         */

        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
    protected void Button3_Click(object sender, EventArgs e)
     {

        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
    protected void Button4_Click(object sender, EventArgs e)
     {
        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();

     }