ASP.NET实现大文件下载

https://support.microsoft.com/zh-cn/kb/812406

http://www.cnblogs.com/luisliu/p/4253815.html

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。

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 。（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。

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[];

            // 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 = "application/octet-stream"; // Set the file type

                Response.AddHeader("Content-Length", dataToRead.ToString());

                Response.AddHeader("Content-Disposition", "attachment; filename=" + filename);

                // Read the bytes.

                while (dataToRead > )

                {

                    // Verify that the client is connected.

                    if (Response.IsClientConnected)

                    {

                        // Read the data in buffer.

                        length = iStream.Read(buffer, , );

                        // Write the data to the current output stream.

                        Response.OutputStream.Write(buffer, , length);

                        // Flush the data to the HTML output.

                        Response.Flush();

                        buffer = new Byte[];

                        dataToRead = dataToRead - length;

                    }

                    else

                    {

                        // Prevent infinite loop if user disconnects

                        dataToRead = -;

                    }

                }

            }

            catch (Exception ex)

            {

                // Trap the error, if any.

                Response.Write("Error : " + ex.Message);

            }

            finally

            {

                if (iStream != null)

                {

                    //Close the file.

                    iStream.Close();

                }

                Response.End();

            }

        }

    }

}

重要说明：当您在 ASP.NET 应用程序的 Web.config 文件中将编译元素的 debug 属性值设置为 false 时，必须针对要下载的文件大小将Server.ScriptTimeout 属性设置为适当的值。默认情况下，Server.ScriptTimeout 值被设置为 90 秒。但是，当 debug 属性被设置为 true时，Server.ScriptTimeout 值将被设置为一个非常大的值（30,000,000 秒）。作为一名开发人员，您必须知道这可能会对您的 ASP.NET Web 应用程序的行为造成的影响。

VB。NET代码如下：

Dim iStream As System.IO.Stream

      ' Buffer to read 10K bytes in chunk:

      Dim buffer() As Byte

      ' Length of the file:

      Dim length As Integer

      ' Total bytes to read:

      Dim dataToRead As Long

      ' Identify the file to download including its path.

      Dim filepath As String = "DownloadFileName"

      ' Identify the file name.

      Dim filename As String = System.IO.Path.GetFileName(filepath)

      Try

         ' Open the file.

         iStream = New System.IO.FileStream(filepath, System.IO.FileMode.Open, _

                                                IO.FileAccess.Read, 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 >

                ' Verify that the client is connected.

                If Response.IsClientConnected Then

                    ' Read the data in buffer

                    length = iStream.Read(buffer, , )

                    ' Write the data to the current output stream.

                    Response.OutputStream.Write(buffer, , length)

                    ' Flush the data to the HTML output.

                    Response.Flush()

                    ReDim buffer() ' Clear the buffer

                    dataToRead = dataToRead - length

                Else

                    'prevent infinite loop if user disconnects

                    dataToRead = -

                End If

            End While

      Catch ex As Exception

         ' Trap the error, if any.

         Response.Write("Error : " & ex.Message)

      Finally

         If IsNothing(iStream) = False Then

            ' Close the file.

            iStream.Close()

         End If

      End Try

巴特西

ASP.NET实现大文件下载

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