ASP.NET (C#) 强制文件下载

Today'sBrowsersarecapableofopeningmanydifferenttypesoffiles.Forexample,ifyouclickonalinktoMP3file,mostBrowserswillplayitwithintheBrowser.Butsometimesyoumaywanttoprovidea'DownloadFile'link,whichwillforcetheBrowsertosavethetargetfileonuser'scomputereveniftheBrowseriscapableofopeningit.RecentlyIworkedonaWebsitethatofferedadownloadoptiontomusicfiles.

InadditiontoforcingdownloadofaFile,youmayalsowanttoperformtaskslikeverifyingiftheuserhasaccesstotheFile,orkeepacountofnumberoftimesaFilehasbeendownloaded.

ThesimpletricktoforcedownloadofaFileisaddingaHTTPheadercalledcontent-disposition=attachment.YoucanalsoaddafilenametothisheadertosuggestaFileNamefortheDownloadedFile.

HereisanASP.NETexamplecode:

01	/***********

02	Author:AbuHaider(http://www.haiders.net)

03

Nov2008

04	AddsExtensionMethod"ForceDownload"toHttpResponseclass

05	Requires:ASP.NET3.5

06	DropthisinApp_Code

07	/************/

08

09

10	public static class HttpExtensions

11

{

12

13	//ForcesDownload/SaveratherthanopeninginBrowser//

14	public static void ForceDownload( this HttpResponseResponse, string virtualPath, string fileName)

15

{

16

17	Response.Clear();

18	Response.AddHeader( "content-disposition" , "attachment;filename=" +fileName);

19	Response.WriteFile(virtualPath);

20	Response.ContentType= "" ;

21	Response.End();

22

23

}

24

25

}

TheexampleaboveisanExtensionmethodforHttpResponse,andwillworkforASP.NET3.5onwards.IfyouaddthisclasstoApp_Code,anewmethodnamed'ForceDownload()'willbeavailableontheResponseobject.HereisanexampleyoucanuseanywhereinanASP.NETPage(Page_LoadEvent,forexample):

1	Response.ForceDownload( "~/Downloads/MyMusic.mp3" , "MyMusic.mp3" );

CallingthismethodwillendtheresponseaftersendingtheFiletoclient.

ForASP.NET2.0,youcanusethebodyoftheExtensionmethodandaddittoPage_LoadEventdirectly.

AboutContentType

TheaboveExtensionMethodsimplyclearstheCotnentTypeheader.Thisistokeepthemethodgeneric.IfyouwouldliketospecifyContentTypeforthetargetFile,youcanaddanotherParametertothemethodandassignittotheContenTypeheaderinsteadofclearingit.ContentTypeheaderisusedbytheBrowsertounderstandwhattypeofdataisbeingreceivedsotheycandisplayitproperlyoruseanassociatedprogramtoopenit.ClearingtheContentTypedoesworkinthiscasesincewedonotwanttheBrowsertotryandopentheFilewithanassociatedprogram,butsimplysaveittodisk.

MyobservationisthatifthereisnoContentTypepresent,IEusesthefileextensiontouderstandthecontent.