ASP.Net下载大文件的实现方法

本文实例讲述了asp.net下载大文件的实现方法。分享给大家供大家参考。具体分析如下：

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 。（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。

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();
            }
        }
    }
}

希望本文所述对大家的asp.net程序设计有所帮助。