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1、URL-RelatedActionsObviouslytheabilitytoimport,link,andredirectisfundamentalinanyJSP-basedwebapplication.TheJSTLprovidesseveralusefulURL-relatedactionstosimplifytheserequirements.TheActionThisactionimportsthecontentofaURL-basedresourceandprovidesasimple,generi
2、cwaytoaccessURL-basedresourcesthatcaneitherbeincludedorprocessedwithintheJSPpage.YoucanseeagoodexampleoftheactionatworkasitworkswithsomeoftheactionsfromtheXMLlibrary,which,ofcourse,requireanXMLdocumenttoworkwith.Theactionisthesimplestwaytoretrieveaf
3、ilecontainingXMLorXSLT,whichisthenusedbysubsequentXMLactionforprocessing.Forexample:Hereyoucanseehowtheactionisusedtoretrieveafilecalledbook.xmlfromaremotelocation,whichisthenutilizedbytheactionfromtheXMLtaglibrary.Notethatinthiscase,becauseofthepres
4、enceofthevarparameter,theactualcontentsofthefilearen’twrittentothecurrentJspWriterbutareinsteadstoredinthenamedparameter.Theactioncanalsobeusedtospecifyabsolute,relative,foreign,context-relative,andFTPURLresourcestoprovidealotmorefunctionalitythatthestandard<
5、jsp:include>actionyou’resousedtohaving.TheActionTheactionprovidesahandywayofconstructingcorrectlyformattedURLsthathavethecorrectURLrewritingrulesapplied.Asyou’renodoubtaware,withoutsessiontrackingortheabilitytorecognizeanumberofrequestsfromthesameuser,the
6、majorityofcomplexweb-basedapplicationswouldn’tbefunctionallypossibleduetothestatelessnessoftheHTTPprotocol.Generally,browsersprovidethesession-trackingmechanismbystoringcookies(smalltextfilesstoredontheclientmachine),whicharesentbackwitheachrequesttheclientmakesduringa
7、“session.”Becausemostmodernbrowsersenabletheusertodisablecookies(usuallyforsecurityreasons),it’sveryimportanttoensurethatanyURLsthatyourwebapplicationsuseareURL-rewrittentoensurethattheirsession-trackingcapabilitiesaremaintainedifcookiesaredisabled.ArewrittenURLlooksso
8、methinglikethis:Asyoucansee,theactualrewritingofaURLsimplyinvolvesappendingaspecialvaluetotheendofthequerystring,whic
