FileUpload控件上传大文件

Uploading Large Files

You must do extra work when uploading large files. You don't want to consume all your server's memory by placing the entire file in memory. When working with a large file, you need to work with the file in more manageable chunks.

First, you need to configure your application to handle large files. Two configuration settings have an effect on posting large files to the server: the httpRuntime maxRequestLength and httpRuntime requestLengthDiskThreshold settings.

The maxRequestLength setting places a limit on the largest form post that the server will accept. By default, you cannot post a form that contains more than 4MB of dataif you try, you'll get an exception. If you need to upload a file that contains more than four megabytes of data, then you need to change this setting.

The requestLengthDiskThreshold setting determines how a form post is buffered to the file system. In the previous version of ASP.NET (ASP.NET 1.1), uploading a large file could do horrible things to your server. The entire file was uploaded into the server memory. While a 10-megabyte video file was uploaded, for example, 10 megabytes of server memory was consumed.

The ASP.NET 2.0 Framework enables you to buffer large files onto the file system. When the size of the file passes the requestLengthDiskThreshold setting, the remainder of the file is buffered to the file system (in the Temporary ASP.NET Files folder).

By default, the ASP.NET framework is configured to buffer any post larger than 80KB to a file buffer. If you are not happy with this setting, then you can modify the requestLengthDiskThreshold to configure a new threshold. (The requestLengthDiskThreshold setting must be less than the maxRequestLength setting.)

The web configuration file in Listing 4.4 enables files up to 10MB to be posted. It also changes the buffering threshold to 100KB.

Listing 4.4. Web.Config

<?xml version="1.0"?> <configuration> <system.web> <httpRuntime maxRequestLength="10240" requestLengthDiskThreshold="100" /> </system.web> </configuration>