Web应用中英文对照外文翻译文献文档格式.docx

Web应用中英文对照外文翻译文献文档格式.docx

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AComparativeStudyofWebApplicationDesignModels

UsingtheJavaTechnologies

Abstract.

TheServlettechnologyhasbeenthemostwidelyusedtechnologyforbuildingscalableWebapplications.Intheevents,therearefourdesignmodelsfordevelopingWebapplicationsusingtheJavatechnologies:

Model1,Model2,Struts,andJavaServerFaces（JSF）.Model1employsaseriesofJSPpages;

Model2adoptstheModel-View-Controllerpattern;

StrutsisaframeworkemployingtheModel2designmodel;

andJSFisanewtechnologythatsupportsready-to-usecomponentsforrapidWebapplicationdevelopment.Model1isnotrecommendedformedium-sizedandlargeapplicationsasitintroducesmaintenancenightmare.Thispapercomparesandevaluatestheeaseofapplicationdevelopmentandtheperformanceofthethreedesignmodels（Model2,Struts,andJSF）bybuildingthreeversionsofanonlinestoreapplicationusingeachofthethreedesignmodels,respectively.

1Introduction

Today,Webapplicationsarethemostcommonapplicationsforpresentingdynamiccontents.ThereareanumberoftechnologiesforbuildingWebapplications,themostpopularofwhichistheServlettechnology.ThistechnologygainsitspopularityfromitssuperiorityoverothertechnologiessuchasCGIandPHP.Servletsarecumbersometodevelop,however,becausesendingHTMLtagsrequirestheprogrammertocomposethemintoaStringobjectandsendthisobjecttothebrowser.Also,aminorchangetotheoutputrequirestheservlettoberecompiled.Toaddressthisissue,SunMicrosystemsinventedJavaServerPages（JSP）.JSPallowsHTMLtagstobeintertwinedwithJavacodeandeachpageistranslatedintoaservlet.AJSPpageisaservlet.However,compilationoccursautomaticallywhenthepageisfirstrequested.Asaresult,changingtheoutputdoesnotneedrecompilation.Inaddition,JSPenablestheseparationofpresentationfromthebusinesslogicthroughtheuseofJavaBeansandcustomtaglibraries.ThenormnowindevelopingJavabasedWebapplicationsistouseservletsalongwithJavaServerPages.

Inthelaterdevelopment,thereareanumberofdesignmodelsforbuildingservlet/JSPapplications:

Model1,Model2,Struts,andJSF.Model1andModel2werefirstmentionedintheearlyspecificationsofJSP.Model1strictlyusesJSPpages,withnoservlets,andModel2usesthecombinationofbothservletsandJSPpages.ThetermsofModel1andModel2havebeenusedeversince.Model1issuitableforprototypesandverysmallapplications,andModel2istherecommendeddesignmodelformediumsizedandlargeapplications.

AsModel2gainedmoreacceptancesintheindustry,anopensourceinitiativetobuildtheStrutsFrameworkwasinitiated.StrutsperfectsModel2byprovidingthecontrollerpartoftheModel-View-ControllerofModel2.Inaddition,Strutsprovidesbetterpagenavigationmanagementandseveralcustomtaglibrariesformorerapiddevelopment.Despiteitssteeplearningcurveandthefactthatitwasneverdefinedinanyspecification,StrutshasbeengainingpopularityasthealternativetoModel2.

JavaServerFacesisbuiltundertheJavaCommunityProcessunderJSR-127.SunMicrosystemsproposedthistechnologyinthehopethatJSFwillbetheultimatemodelforbuildingJavaWebapplications.ThemostimportantfeatureofJSFistheavailabilityofready-to-usecomponentssuchasextensibleUIcomponents,easypagenavigation,inputvalidators,dataconvertersandJavaBeansmanagement.

Theproblemfacingservlet/JSPprogrammersaretochoosethemostappropriatedesignmodel.Clearly,JSFprovidesabettersolutioninregardtodevelopmenttime.However,somepeoplearenotsanguinetoadoptthistechnologyforfearofperformancepenaltyduetotheoverheadoftheJSFimplementation.

WebuildthreeversionsofanonlinestoreapplicationnamedBuyDirectusingModel2,StrutsandJSF.Theparameterscomparedarethenumberoflinesofcode,thenumberofclasses,andtheperformancemeasurementresults.Weinvestigatewhichofthedesignmodelsallowsthemostrapiddevelopmentprocess.Weevaluatetheperformancesoftheapplicationsbuiltuponthesemodels.Weprovidesomesuggestionstoperfecttheexistingdesignmodelstomakedevelopmentmorerapid.

Therestofthepaperisorganisedasfollows.Section2discussestheissuesinWebdevelopment.Section3explainshowthethreedesignmodelsaddressthesedevelopmentissues.Section4providesthedetailsofthehardwareandsoftwareusedintheseexperiments.Section5presentstheexperimentresultsandanalysis.Section6reviewstherelatedwork.Section7concludesbyofferingsomesuggestionstoimprovetheexistingdesignmodels.

2JavaWebDevelopmentIssues

AllJavaWebdevelopmentusestheServlettechnologyastheunderlyingtechnology.Assuch,allJavaWebapplicationshavecertainissuesthatneedtobeaddressed:

●UserInterface.TheuserinterfaceiswhattheclientbrowserrendersasHTMLtags.Anyserver-sidecomponentusedintheapplicationmustbeencodedintothecorrespondingHTMLelements.Besidesfordisplayingthecontentanddata,theuserinterfaceisalsoresponsibleinreceivinginputfromtheuser.

●InputValidation.Userinputneedstobevalidated.Therearetwotypesofinputvalidation,server-sideandclient-side.Asthenameimplies,theserver-sideinputvalidationisperformedontheserveraftertheinputreachestheserver.Client-sideinputvalidationisdoneonthebrowser,usuallybyusingJavaScriptorotherscriptinglanguages.Theadvantagesofusingclient-sideinputvalidationarepromptresponseandreducingtheserverworkload.Theserver-sideinputvalidationshouldalwaysbeperformedregardlessthepresenceofclient-sidevalidationbecausethereisnoguaranteetheuserbrowser'

sscriptingfeatureisbeingonandmalicioususerscaneasilyworkaroundclient-sidevalidation.

●ModelObjects.ModelobjectsinJava-basedWebapplicationsareintheformsofJavaBeans.ModelobjectsmakeuptheModelpartoftheMVCbaseddesignmodel.Amodelobjectcanbeusedtobindacomponentvaluetobeusedatalaterstage.Inaddition,itcanencapsulatebusinesslogicrequiredforprocessing.

●PageNavigation.AlmostallWebapplicationshavemultiplepagesthattheusercannavigatefromonetoanother.AllMVC-baseddesignmodelsuseaservletastheControllerpart.Thisservletalsoactsasthesoleentrypointtotheapplication.Whichpagetobedisplayedafterthecurrentrequestisdeterminedbythevalueofaspecifiedrequestparameter.Managingpagenavigationiscriticallyimportant.

3WebApplicationDesignModels

TheModel2designmodelisbasedontheModel-View-Controller（MVC）designpattern.AsexplainedbyBurbeck,therearethreemainmodulesinMVC,theController,theView,andtheModel.TheControlleractsasthecentralentrypointtotheapplication.Alluserinteractionsgothroughthiscontroller.TheViewcontainsthepresentationpartoftheapplication,andtheModelstoresdataorencapsulatesbusinesslogicoftheapplication.Inthelaterdevelopment,theStrutsFrameworkprovidesacommonframeworktoeasilybuildModel2applications.Then,thelastinitiativeistheJavaServerFaces,whichalsoemploystheMVCdesignpattern.

Inthefollowingsections,wediscussthesethreedesignmodelsandexplainhoweachdesignmodeladdressesthedevelopmentissuesspecifiedintheprevioussection.

3.1Model2

AJavaWebapplicationthatisbasedontheModel2designmodelhasoneservlet（calledtheControllerservlet）thatservesastheControllerpart.Allrequestsarefirsthandledbythisservlet,whichimmediatelydispatchestherequeststotheappropriateviewsusingRequestDispatcherobjects.ViewsintheModel2designmodelarerepresentedbyJSPpages.Tostoredata,aModel2applicationusesJavaBeans,whicharetheModelpartoftheapplication.Inadditiontostoringdata,theJavaBeansalsoencapsulatebusinesslogic.EachHTTPrequestcarriesanactionparameterthatindicateswhichviewtodispatchthisrequestto.TheprogrammermustcodetheHTMLtagsforuserinterfaceinallJSPpagesintheapplicationandwriteinputvalidationcode.Inaddition,themodelobjectsaremanagedbyindividualJSPpages.

3.2Struts

TheStrutsFrameworkisanimprovementoftheModel2designmodel.ItprovidesadefaultControllerservletsothattheuserdoesnothavetowriteandcompileone.Strutsalleviatesthetaskofpagenavigationbyallowingnavigationrulestobepresentinitsapplicationconfigurationfile（anXMLdocument）.ChangestothenavigationrulesdonotrequirerecompilationofaJavaservletclass.Inadditiontoeasierpagenavigation,StrutsprovidescustomtaglibrariesthatdefinetagsrepresentingHTMLelements.OneofthesetagsisusedforerrorhandlingandStrutsisthereforecapableofdisplayinglocalizederrormessagesinsupportforinternationalization.StrutsapplicationsuseJavaBeansastheirmodels,justliketheModel2designmodel.Inaddition,Strutsprogrammershavetowritetheirowninputvalidationcode.

3.3JSF

JSFalsoemploysacontrollerservletthatiscalledFacesServlet.ThisservletistheonlyentrypointtoaJSFapplication.JSFalsousesJSPpagesasitsviewsandJavaBeansasitsmodelobjects.UnlikeModel2andStruts,however,JSFprovidesready-to-useuserinterfacecomponentsthatcanbewrittenonJSPpages.UponaninvocationofapageofaJSFapplication,theFacesServletconstructsacomponenttreethatrepresentstheJSPpagebeingrequested.Someofthecomponentscanalsotriggerevents,makingJSFevent-driven.Forpagenavigation,JSFusesanapproachsimilartoStruts,i.e.,byallowingnavigationrulestobede