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 protected void Page_Load(object sender, EventArgs e)
    {
        try
        {
            //获取文件路径
            string filepath = Server.MapPath("xmsbry/upload/b/") + Request.QueryString["filename"];
            if (System.IO.File.Exists(filepath))
            {
                Download(filepath); System.IO.File.Delete(filepath);
            }
            else
            {  
                Response.Write("<script>alert('文件丢失，请联系管理员！');this.close();</script>");
            }
        }
        catch
        {
            //Response.Write("<script>alert('"+ex.ToString()+"');this.close();</script>");
        }

    }

protected void Download(string filepath)
    {
        System.IO.Stream iStream = null;

        // Buffer to read 10K bytes in chunk:
        byte[] buffer = new Byte[10000];

        // Length of the file:
        int length;

        // Total bytes to read:
        long dataToRead;

        // Identify the file to download including its path. 
        // Identify the file name.
        string filename = System.IO.Path.GetFileName(filepath);

        try
        {
            // Open the file.
            iStream = new System.IO.FileStream(filepath, System.IO.FileMode.Open,
            System.IO.FileAccess.Read, System.IO.FileShare.Read);


            // Total bytes to read:
            dataToRead = iStream.Length;

            Response.ContentType = "application/octet-stream";
            Response.AddHeader("Content-Disposition", "attachment; filename=" + filename);

            // Read the bytes.
            while (dataToRead > 0)
            {
                // Verify that the client is connected.
                if (Response.IsClientConnected)
                {
                    // Read the data in buffer.
                    length = iStream.Read(buffer, 0, 10000);

                    // Write the data to the current output stream.
                    Response.OutputStream.Write(buffer, 0, length);

                    // Flush the data to the HTML output.
                    Response.Flush();

                    buffer = new Byte[10000];
                    dataToRead = dataToRead - length;
                }
                else
                {
                    //prevent infinite loop if user disconnects
                    dataToRead = -1;
                }
            } 
        }
        catch (Exception ex)
        {
            // Trap the error, if any.
            Response.Write("Error : " + ex.Message);
        }
        finally
        {
            if (iStream != null)
            {
                //Close the file.
                iStream.Close();
            }
        }  
    }