【精品文档】532关于计算机专业JSP表达式语言介绍简介概述的毕业设计论文英文英语外文文献翻译成品资料:JSP和EL介绍中英文双语对照15.docx
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【精品文档】532关于计算机专业JSP表达式语言介绍简介概述的毕业设计论文英文英语外文文献翻译成品资料:JSP和EL介绍中英文双语对照15.docx
《【精品文档】532关于计算机专业JSP表达式语言介绍简介概述的毕业设计论文英文英语外文文献翻译成品资料:JSP和EL介绍中英文双语对照15.docx》由会员分享,可在线阅读,更多相关《【精品文档】532关于计算机专业JSP表达式语言介绍简介概述的毕业设计论文英文英语外文文献翻译成品资料:JSP和EL介绍中英文双语对照15.docx(35页珍藏版)》请在冰豆网上搜索。
本文是中英对照毕业设计论文外文文献翻译,下载后直接可用!
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文献引用作者出处信息:
VivekChopraBeginningJavaServerPages,2020(如觉得年份太老,可改为近2年,毕竟很多毕业生都这样做)
英文4392单词,26007字符(字符就是印刷符),中文7232汉字。
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JSPandEL
ThepreviouschaptersinthisbookdemonstratedthebreadthofJSPtechnologyandintroducedsomebasictechniquesofJSPdevelopment.Theaimthusfarhasbeentoprovideyouwithsomefast,hands-onexperiencewiththeJSPtechnology.TheworkingexamplesintheseearlierchaptersenabledyoutotryoutrealJSPcode,andseewhatJSPcanbeusedforintherealworld.
Unliketheearlierchapters,thischapterprovidesamorein-depthexplorationofacornerstoneelementoftheJSPstandard:
JSP’sExpressionLanguage,orELforshort.
Inthischapter,youwilldiscoverthefollowing:
❑WhyELisanindispensablepartofJSP2.0
❑HowtouseELnamedvariables
❑HowtoperformtypeconversionandcoercioninEL
❑HowtohandlenullvaluesinEL
❑Howtoworkwitharithmetic,logical,comparison,andotheroperatorsinEL
❑ThedifferentwaysofaccessingmembersofacollectioninEL
❑HowtoaccesspropertiesofobjectsinEL
❑HowtoaccessnestedobjectpropertiesinEL
❑HowtouseimplicitobjectsinEL
❑HowtodefineandaccessfunctionsinEL
❑HowtouseanamespacewhenreferencingELfunctions
Thischaptercoversalotofground,andincludesfiveseparateexamples.Bytheendofthechapter,youshouldbeveryfamiliarwithEL,andbecomfortableusingitinyourownapplications.
ELandItsVitalRoleinJSP
ELwasnotpartoftheJSPstandardpriorto2.0.OneofthemainreasonsforcreatingELwastoensurethatpresentation-levelJSPpagescouldbecreatedwithoutrelyingonscriptingelements.Chapter3,“JSPBasics2:
GeneralizedTemplatingandServerScripting,”coveredtheuseofscriptingelements(typicallycodewritteninJava)thatareembeddedwithinaJSPpage.
TheneedforscriptingelementswithinJSPistypicallydrivenbytherequirementsofanapplication.
Majorapplicationrequirementsthatdemandtheuseofscriptingelementsincludethefollowing:
❑Toprovidecontrol-flowforJSPexecution
❑Toset,andsubsequentlyaccess,variablesthatarelocaltotheJSPpage
❑TorenderavaluefromacomplexexpressionthatinvolvesJavaobjects
❑ToaccesspropertiesofanarbitraryJavaobject
❑TocallmethodsofJavaBeansorotherJavaobjects
Unfortunately,experiencehasshownthattheuseofscriptingelementsinJSPsmakeslargeprojectsdiffi-culttomaintainoverthelongterm.Italsoencouragesprogrammingpracticesthatmaytightlycouplethepresentation(userinterface)ofanapplicationtoitsbusinesslogic,reducingitsflexibilityandscala-bility.ThisisahighlyundesirablepracticeinthecreationofWebapplicationsandservices.Ideally,JSPsshouldbecreatedfreeofscriptingelementsifatallpossible.
InordertocreateaJSPversionthatcanworkcompletelyfreeofscriptingelements,itisessentialthatallfiveoftheapplicationrequirementscanbesatisfiedwithouttheuseofembeddedJavacoding.JSP2.0satisfiestheserequirements.ThefirsttwoitemsarehandledbyJSTL(exploredindetailinChapter6,“JSPTagLibrariesandJSTL”),whilethelastthreerequirementsarehandledbyEL.
ELisindependentofJSP2.0.DespitethevitalroleofELinJSP2.0,theuseofELisnotexclusivetoJSPcontainers.TheELparserisalsonottightlyintegratedintotheJSPparser,butcanbedetachedandreusedforotherpurposes.Infact,ELisincorporatedintobothJavaServerFaces(JSF,aserver-sideGUIconstructionkittechnology;seeChapter21,“JavaServerFaces,”formoreinformation),andJSTL.Therefore,becomingfamiliarwithELwillsaveyoutimewhenexploringtheseothertechnologies.
ELNamedVariables
WhenworkingwithEL(andJSTL),youwillfrequentlyworkwithnamedvariables.NamedvariablesinELrefertoattributesattachedtoJSPscopingobjects.Forexample,thefollowingELexpressionwillren-derthevalueofthenamedvariablecalledbearCount:
TheELparserwillsearchfortheattributethroughthevariousJSPscopingobjectsinthefollowingorder:
1Page
2.Request
Session(ifcurrentlyvalid)
Application
Inpractice,thisisequivalenttoacalltotheJavaPageContext.findAttribute()method.IfyouaremaintaininglegacyJSPcodewithembeddedJava,youmayseethiscall.YoucanconsulttheJSPJavadocs(APIdocumentation)toseehowthismethodworks.
Figure5-1illustratesthesearchforanELnamedvariable.
Figure5-1:
OrderofsearchforanELnamedvariable
InFigure5-1,youcanseethesearchorderforanELnamedvariable:
FirstthesetofELimplicitobjectsissearchedforamatchingname(ELimplicitobjectsarecoveredlaterinthischapter),andthenthefourscopes.Ifthenamedvariableisn
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