ASP网站制作之Caching in ASP.NET

asp可以使用微软的activeX使得网页功能无比强大，不过安全性也较差，而且是基于的windows服务器，所以性能稳定性也一般asp.netThemajority[ifnotall]ofthepagesinadynamicwebsitearedynamic.Thatis,pagesthatarecreatedonuserrequest.Asweallknow,dynamicwebpageshelptoprovidedynamiccontent,customizedfortheuserrequestingthepage[e.g.:theusershomepage].Dynamicpagesalsohelpprovidedynamiccontentfetchedfromachangingdatastorewithouttheneedfortheadministratortochangethepagecontenteverytimesomethingchangesinthedatastore[e.g.:Listingofbooksinapublisherswebsite].Thedisadvantageistheoverheadincreatingthepagesforeveryuserrequest.

Toovercomethis,somewebsiteshavepagecreationengineswhichcreateallpagesinonegoandsavethemasHTMLpageswhicharethenservedtotheusers.Butthiswillonlyhelpinscenarioswherethepagecontentisthesameforallrequests[user-independent]asinthesecondexampleabove.Thelistingofbooksisthesameirrespectiveoftheuserrequestingthepage.EvenifthereisprovisionforlistingbookscategorywisebyprovidingdifferentcategoryIDvaluesthroughthequerystring,thepageoutputforaparticularcategoryofbooksisthesameforallusers.

ASP.NETprovidessupportfor"caching"whichwillhelpussolvethisproblemtoagreatextend.Itcancache[storeinmemory]theoutputgeneratedbyapageandwillservethiscachedcontentforfuturerequests.Andthisisusefulonlyinthesecondscenariodescribedearlier,wherethepagecontentisthesameforallrequests[user-independent].Thecachingfeatureiscustomizableinvariouswaysandwewillseehowwecandothataswegothroughthisarticle.

Cachingapage
Inordertocacheapagesoutput,weneedtospecifyan@OutputCachedirectiveatthetopofthepage.Thesyntaxisasshownbelow:

<%@OutputCacheDuration=5VaryByParam="None"%>
Asyoucansee,therearetwoattributestothisdirective.Theyare:

Duration-Thetimeinsecondsofhowlongtheoutputshouldbecached.Afterthespecifieddurationhaselapsed,thecachedoutputwillberemovedandpagecontentgeneratedforthenextrequest.Thatoutputwillagainbecachedfor10secondsandtheprocessrepeats.
VaryByParam-Thisattributeiscompulsoryandspecifiesthequerystringparameterstovarythecache.
Intheabovesnippet,wehavespecifiedtheVaryByParamattributeasNonewhichmeansthepagecontenttobeservedisthesameregardlessoftheparameterspassedthroughthequerystring[seeExample1inthesampledownload].

Iftherearetworequeststothesamepagewithvaryingquerystringparameters,e.g.:.../PageCachingByParam.aspx?id=12and.../PageCachingByParam.aspx?id=15]andseparatepagecontentisgeneratedforeachofthem,thedirectiveshouldbe:

<%@OutputCacheDuration=5VaryByParam="id"%>
ThepagecontentforthetworequestswilleachbecachedforthetimespecifiedbytheDurationattribute[seeExample2inthesampledownload].

Tospecifymultipleparameters,usesemicolontoseparatetheparameternames.IfwespecifytheVaryByParamattributeas*,thecachedcontentisvariedforallparameterspassedthroughthequerystring.

Somepagesgeneratedifferentcontentfordifferentbrowsers.Insuchcases,thereisprovisiontovarythecachedoutputfordifferentbrowsers.The@OutputCachedirectivehastobemodifiedto:

<%@OutputCacheDuration=5VaryByParam="id"VaryByCustom="browser"%>
Thiswillvarythecachedoutputnotonlyforthebrowserbutalsoitsmajorversion.I.e.,IE5,IE6,Netscape4,Netscape6willallgetdifferentcachedversionsoftheoutput.

Cachingpagefragments
Sometimeswemightwanttocachejustportionsofapage.Forexample,wemighthaveaheaderforourpagewhichwillhavethesamecontentforallusers.Theremightbesometext/imageintheheaderwhichmightchangeeveryday.Inthatcase,wewillwanttocachethisheaderforadurationofaday.

Thesolutionistoputtheheadercontentsintoausercontrolandthenspecifythattheusercontrolcontentshouldbecached.Thistechniqueiscalledfragmentcaching.

Tospecifythatausercontrolshouldbecached,weusethe@OutputCachedirectivejustlikeweuseditforthepage.

<%@OutputCacheDuration=10VaryByParam="None"%>
Withtheabovedirective,theusercontrolcontentwillbecachedforthetimespecifiedbytheDurationattribute[10secs].Regardlessofthequerystringparametersandbrowsertypeand/orversion,thesamecachedoutputisserved.[SeeExample3inthedownloadforademonstration].

DataCaching
ASP.NETalsosupportscachingofdataasobject</p>asp可以使用微软的activeX使得网页功能无比强大，不过安全性也较差，而且是基于的windows服务器，所以性能稳定性也一般

Request:从字面上讲就是“请求”，因此这个是处理客户端提交的东东的,例如Resuest.Form，Request.QueryString,或者干脆Request("变量名")

封装性使得代码逻辑清晰，易于管理，并且应用到ASP.Net上就可以使业务逻辑和Html页面分离，这样无论页面原型如何改变，业务逻辑代码都不必做任何改动；继承性和多态性使得代码的可重用性大大提高。

如何学好ASP,以前也有人问过,把回答给你转过来看看能否对你有帮助:

我可以结合自己的经验大致给你说一说，希望对你有所帮助，少走些弯路。

代码的可重用性差：由于是面向结构的编程方式，并且混合html，所以可能页面原型修改一点，整个程序都需要修改，更别提代码重用了。

不能只是将它停留在纸上谈兵的程度上。

我想问如何掌握学习节奏(先学什么再学什么)最好详细点?

多看多学多思。多看一些关于ASP的书籍，一方面可以扩展知识面一方面可以鉴借别人是如何掌握、运用ASP的;多学善于关注别人，向同学老师多多学习，不论知识的大小;多思则是要将学到的知识灵活运用。

它可通过内置的组件实现更强大的功能，如使用A-DO可以轻松地访问数据库。

我就感觉到ASP和一些常用的数据库编程以及软件工程方面的思想是非常重要的。我现在也在尝试自己做网页，这其中就用到了ASP，我想它的作用是可想而知的。

ASP.Net摆脱了以前ASP使用脚本语言来编程的缺点，理论上可以使用任何编程语言包括C++,VB,JS等等，当然，最合适的编程语言还是MS为.NetFrmaework专门推出的C(读csharp)，它可以看作是VC和Java的混合体吧。