當(dāng)我們的網(wǎng)站需要支持下載大文件時，如果不做控制可能會導(dǎo)致用戶在訪問下載頁面時發(fā)生無響應(yīng)，使得瀏覽器崩潰。可以參考如下代碼來避免這個問題。
1. 將數(shù)據(jù)分成較小的部分，然后將其移動到輸出流以供下載，從而獲取這些數(shù)據(jù)。
2. 根據(jù)下載的文件類型來指定 Response.ContentType 。（參考OSChina的這個網(wǎng)址可以找到大部分文件類型的對照表：http://tool.oschina.net/commons）
3. 在每次寫完response時記得調(diào)用 Response.Flush()
4. 在循環(huán)下載的過程中使用 Response.IsClientConnected 這個判斷可以幫助程序盡早發(fā)現(xiàn)連接是否正常。若不正常，可以及早的放棄下載，以釋放所占用的服務(wù)器資源。
5. 在下載結(jié)束后，需要調(diào)用 Response.End() 來保證當(dāng)前線程可以在最后被終止掉。
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();
}
}
}
}
