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外文资料JavaServerPagesOverviewJavaServerPages(JSP)technologyenablesWebdevelopersanddesignerstorapidlydevelopandeasilymaintain,information-rich,dynamicWebpagesthatleverageexistingbusinesssystems.AspartoftheJavatechnologyfamily,JSPtechnologyenablesrapiddevelopmentofWeb-basedapplicationsthatareplatformindependent.JSPtechnologyseparatestheuserinterfacefromcontentgeneration,enablingdesignerstochangetheoverallpagelayoutwithoutalteringtheunderlyingdynamiccontent.BenefitsforDevelopersIfyouareaWebpagedeveloperordesignerwhoisfamiliarwithHTML,youcan:UseJSPtechnologywithouthavingtolearntheJavalanguage:YoucanuseJSPtechnologywithoutlearninghowtowriteJavascriplets.Althoughscriptletsarenolongerrequiredtogeneratedynamiccontent,theyarestillsupportedtoprovidebackwardcompatibility.ExtendtheJSPlanguage:JavataglibrarydevelopersanddesignerscanextendtheJSPlanguagewithsimpletaghandlers,whichutilizeanew,muchsimplerandcleaner,tagextensionAPI.Thisspursthegrowingnumberofpluggable,reusabletaglibrariesavailable,whichinturnreducestheamountofcodeneededtowritepowerfulWebapplications.Easilywriteandmaintainpages:TheJavaServerPagesStandardTagLibrary(JSTL)expressionlanguageisnowintegratedintoJSPtechnologyandhasbeenupgradedtosupportfunctions.Theexpressionlanguagecannowbeusedinsteadofscriptletexpressions.JSPTechnologyandJavaServletsJSPtechnologyusesXML-liketagsthatencapsulatethelogicthatgeneratesthecontentforthepage.Theapplicationlogiccanresideinserver-basedresources(suchasJavaBeanscomponentarchitecture)thatthepageaccesseswiththesetags.Anyandallformatting(HTMLorXML)tagsarepasseddirectlybacktotheresponsepage.Byseparatingthepagelogicfromitsdesignanddisplayandsupportingareusablecomponent-baseddesign,JSPtechnologymakesitfasterandeasierthanevertobuildWeb-basedapplications.JavaServerPagestechnologyisanextensionoftheJavaServlettechnology.Servletsareplatform-independent,server-sidemodulesthatfitseamlesslyintoaWebserverframeworkandcanbeusedtoextendthecapabilitiesofaWebserverwithminimaloverhead,maintenance,andsupport.Unlikeotherscriptinglanguages,servletsinvolvenoplatform-specificconsiderationormodifications;theyareapplicationcomponentsthataredownloaded,ondemand,tothepartofthesystemthatneedsthem.Together,JSPtechnologyandservletsprovideanattractivealternativetoothertypesofdynamicWebscripting/programmingbyoffering:platformindependence;enhancedperformance;separationoflogicfromdisplay;easeofadministration;extensibilityintotheenterprise;and,mostimportantly,easeofuse.TodayservletsareapopularchoiceforbuildinginteractiveWebapplications.Third-partyservletcontainersareavailableforApacheWebServer,MicrosoftIIS,andothers.ServletcontainersareusuallyacomponentofWebandapplicationservers,suchasBEAWebLogicApplicationServer,IBMWebSphere,SunJavaSystemWebServer,SunJavaSystemApplicationServer,andothers.CommunityBackgroundTheJSPspecificationistheproductofindustry-widecollaborationwithindustryleadersintheenterprisesoftwareandtoolsmarkets,ledbySunMicrosystems.SunhasmadetheJSPspecificationfreelyavailabletothedevelopercommunity,withthegoalthateveryWebserverandapplicationserverwillsupporttheJSPinterface.JSPpagessharetheWriteOnce,RunAnywhereadvantagesofJavatechnology.JSPtechnologyisakeycomponentintheJava2Platform,EnterpriseEdition,Sun'shighlyscalablearchitectureforenterpriseapplications.JSPTechnologyintheJavaEE5PlatformThefocusofJavaEE5hasbeeneaseofdevelopmentbymakinguseofJavalanguageannotationsthatwereintroducedbyJ2SE5.0.JSP2.1supportsthisgoalbydefiningannotationsfordependencyinjectiononJSPtaghandlersandcontextlisteners.AnotherkeyconcernoftheJavaEE5specificationhasbeenthealignmentofitswebtiertechnologies,namelyJavaServerPages(JSP),JavaServerFaces(JSF),andJavaServerPagesStandardTagLibrary(JSTL).TheoutcomeofthisalignmentefforthasbeentheUnifiedExpressionLanguage(EL),whichintegratestheexpressionlanguagesdefinedbyJSP2.0andJSF1.1.ThemainkeyadditionstotheUnifiedELthatcameoutoftbealignmentworkhavebeen:ApluggableAPIforresolvingvariablereferencesintoJavaobjectsandforresolvingthepropertiesappliedtotheseJavaobjects,Supportfordeferredexpressions,whichmaybeevaluatedbyataghandlerwhenneeded,unliketheirregularexpressioncounterparts,whichgetevaluatedimmediatelywhenapageisexecutedandrendered,andSupportforlvalueexpression,whichappearonthelefthandsideofanassignmentoperation.Whenusedasanlvalue,anELexpressionrepresentsareferencetoadatastructure,forexample:aJavaBeansproperty,thatisassignedsomeuserinput.ThenewUnifiedELisdefinedinitsownspecificationdocument,whichisdeliveredalongwiththeJSP2.1specification.ThankstotheUnifiedEL,JSTLtags,suchastheJSTLiterationtags,cannowbeusedwithJSFcomponentsinanintuitiveway.JavaServletTechnologyOverviewServletsaretheJavaplatformtechnologyofchoiceforextendingandenhancingWebservers.Servletsprovideacomponent-based,platform-independentmethodforbuildingWeb-basedapplications,withouttheperformancelimitationsofCGIprograms.Andunlikeproprietaryserverextensionmechanisms(suchastheNetscapeServerAPIorApachemodules),servletsareserver-andplatform-independent.Thisleavesyoufreetoselectabestofbreeds