ASP.NET 大文件下载的实现思路及代码

　文件下载是一个网站最基本的功能，ASP.NET网站的文件下载功能实现也很简单，但是如果遇到大文件的下载而不做特殊处理的话，那将会出现不可预料的后果。本文就基于ASP.NET提供大文件下载的实现思路及代码。

 

 

　　当我们的网站需要支持下载大文件时，如果不做控制可能会导致用户在访问下载页面时发生无响应，使得浏览器崩溃。可以参考如下代码来避免这个问题。

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using System; namespace WebApplication1 {     public partial class DownloadFile : System.Web.UI.Page     {         protected void Page_Load(object sender, EventArgs e)         {             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.             string filepath = Server.MapPath("/") +"./Files/TextFile1.txt";             // 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.Clear();                 Response.ClearHeaders();                 Response.ClearContent();                 Response.ContentType = "text/plain"; // Set the file type                 Response.AddHeader("Content-Length", dataToRead.ToString());                 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();                 }                 Response.End();             }         }     } }

　　关于此代码的几点说明：

　　1. 将数据分成较小的部分，然后将其移动到输出流以供下载，从而获取这些数据。

　　2. 根据下载的文件类型来指定 Response.ContentType 。（参考OSChina的这个网址可以找到大部分文件类型的对照表：http://tool.oschina.net/commons）

　　3. 在每次写完response时记得调用 Response.Flush()

　　4. 在循环下载的过程中使用 Response.IsClientConnected 这个判断可以帮助程序尽早发现连接是否正常。若不正常，可以及早的放弃下载，以释放所占用的服务器资源。

　　5. 在下载结束后，需要调用 Response.End() 来保证当前线程可以在最后被终止掉。