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。
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。