英文.docx

英文.docx

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英文

Abstract

KidsingradeschoolputHTMLpagesontheInternet.However,thereisamonumentaldifferencebetweenagradeschoolpageandaprofessionallydevelopedWebsite.Thepagedesigner（orHTMLdeveloper）mustunderstandcolors,thecustomer,productflow,pagelayout,browsercompatibility,imagecreation,JavaScript,andmore.Puttingagreatlookingsitetogethertakesalotofwork,andmostJavadevelopersaremoreinterestedincreatingagreatlookingobjectinterfacethanauserinterface.JavaServerPages（JSP）technologyprovidesthegluebetweenthepagedesignerandtheJavadeveloper.

Ifyouhaveworkedonalarge-scaleWebapplication,youunderstandthetermchange.Model-View-Controller（MVC）isadesignpatternputtogethertohelpcontrolchange.MVCdecouplesinterfacefrombusinesslogicanddata.StrutsisanMVCimplementationthatusesServlets2.2andJSP1.1tags,fromtheJ2EEspecifications,aspartoftheimplementation.YoumayneverimplementasystemwithStruts,butlookingatStrutsmaygiveyousomeideasonyourfutureServletsandJSPimplementations.oucarefullystudytherealapplication,youwillfindtheprogramgenerallycomposedoftwodifferenttypesofcomponents,andprocedurestodealwithspecificmattersarecloselyrelated,wemightcallthembusinesscomponents;otherapplicationservices.Forexample:

ataxcollectionsystemandalibrarymanagementsystemthereisabigdifferenceinhandlingtheirbusiness,dealdirectlywiththebusinesscomponentsduetothedifferentnatureofthebusinessisunlikelytobereusedindifferentsystems,whileotherscomponentssuchastheseonlyrelatedtotheprogramcomponentoftheprogramflowofcontrol,inputvalidation,errorhandlingandtaglibraryinthedifferentsystemscanbereused.Peoplewillnaturallywanttoextractthesedifferentapplicationshaveincommonsomethingsout,made​​asemi-finishedprogram,thissemi-finishedproductsistheso-calledproceduralframeworktodoanewthingwhentheydonothavetostartfromscratch,butcanbegantobuildonthisfoundation.Infact,somelargesoftwarecompanieshavechosentobuildsuchaframework.Butmostsmallandmedium-sizedsoftwarecompaniesorotherorganizations,therearenoconditionstoestablishaframework.Strutsasanopensourceapplicationframework,inrecentyearshasbeenrapiddevelopmentofveryextensiveapplicationinJSPWebapplicationdevelopment,someoftheliteraturethatithasbecomethedefactostandardoftheJSPWebapplicationframework.

Keywords:

Internet,Struts,interface,implementation

Model-View-Controller（MVC）

JSPtagssolvedonlypartofourproblem.Westillhaveissueswithvalidation,flowcontrol,andupdatingthestateoftheapplication.ThisiswhereMVCcomestotherescue.MVChelpsresolvesomeoftheissueswiththesinglemoduleapproachbydividingtheproblemintothreecategories:

∙Model

Themodelcontainsthecoreoftheapplication'sfunctionality.Themodelencapsulatesthestateoftheapplication.Sometimestheonlyfunctionalityitcontainsisstate.Itknowsnothingaboutthevieworcontroller.

∙View

Theviewprovidesthepresentationofthemodel.Itisthelookoftheapplication.Theviewcanaccessthemodelgetters,butithasnoknowledgeofthesetters.Inaddition,itknowsnothingaboutthecontroller.Theviewshouldbenotifiedwhenchangestothemodeloccur.

∙Controller

Thecontrollerreactstotheuserinput.Itcreatesandsetsthemodel.

MVCModel

TheWebbroughtsomeuniquechallengestosoftwaredevelopers,mostnotablythestatelessconnectionbetweentheclientandtheserver.Thisstatelessbehaviormadeitdifficultforthemodeltonotifytheviewofchanges.OntheWeb,thebrowserhastore-querytheservertodiscovermodificationtothestateoftheapplication.

Anothernoticeablechangeisthattheviewusesdifferenttechnologyforimplementationthanthemodelorcontroller.Ofcourse,wecoulduseJava（orPERL,C/C++orwhatever）codetogenerateHTML.Thereareseveraldisadvantagestothatapproach:

∙Javaprogrammersshoulddevelopservices,notHTML.

∙Changestolayoutwouldrequirechangestocode.

∙Customersoftheserviceshouldbeabletocreatepagestomeettheirspecificneeds.

∙Thepagedesignerisn'tabletohavedirectinvolvementinpagedevelopment.

∙HTMLembeddedintocodeisugly.

FortheWeb,theclassicalformofMVCneededtochange.Figure4displaystheWebadaptationofMVC,alsocommonlyknownasMVCModelorMVC2.

Figure4.MVCModel2

Struts,anMVCimplementation

Strutsisasetofcooperatingclasses,servlets,andJSPtagsthatmakeupareusableMVC2design.ThisdefinitionimpliesthatStrutsisaframework,ratherthanalibrary,butStrutsalsocontainsanextensivetaglibraryandutilityclassesthatworkindependentlyoftheframework.Figure5displaysanoverviewofStruts.

Figure5.Strutsoverview

StrutsIntroductionanddetails

Introduction

∙Clientbrowser

AnHTTPrequestfromtheclientbrowsercreatesanevent.TheWebcontainerwillrespondwithanHTTPresponse.

∙Controller

TheControllerreceivestherequestfromthebrowser,andmakesthedecisionwheretosendtherequest.WithStruts,theControllerisacommanddesignpatternimplementedasaservlet.Thestruts-config.xmlfileconfigurestheController.

∙Businesslogic

Thebusinesslogicupdatesthestateofthemodelandhelpscontroltheflowoftheapplication.WithStrutsthisisdonewithanActionclassasathinwrappertotheactualbusinesslogic.

∙Modelstate

Themodelrepresentsthestateoftheapplication.Thebusinessobjectsupdatetheapplicationstate.ActionFormbeanrepresentstheModelstateatasessionorrequestlevel,andnotatapersistentlevel.TheJSPfilereadsinformationfromtheActionFormbeanusingJSPtags.

∙View

TheviewissimplyaJSPfile.Thereisnoflowlogic,nobusinesslogic,andnomodelinformation--justtags.TagsareoneofthethingsthatmakeStrutsuniquecomparedtootherframeworkslikeVelocity.

Note:

"Thinkthin"whenextendingtheActionclass.TheActionclassshouldcontroltheflowandnotthelogicoftheapplication.ByplacingthebusinesslogicinaseparatepackageorEJB,weallowflexibilityandreuse.

AnotherwayofthinkingaboutActionclassisastheAdapterdesignpattern.ThepurposeoftheActionisto"Converttheinterfaceofaclassintoanotherinterfacetheclientsexpect.Adapterletsclassesworktogetherthatcouldn_totherwisebecauseofincompatibilityinterface"（fromDesignPatterns-ElementsofReusableOOSoftwarebyGof）.TheclientinthisinstanceistheActionServletthatknowsnothingaboutourspecificbusinessclassinterface.Therefore,Strutsprovidesabusinessinterfaceitdoesunderstand,Action.ByextendingtheAction,wemakeourbusinessinterfacecompatiblewithStrutsbusinessinterface.（AninterestingobservationisthatActionisaclassandnotaninterface.Actionstartedasaninterfaceandchangedintoaclassovertime.Nothing'sperfect.）

Process

Entertheusernamepasswordsubmittheformsubmittedtotheactionattributeoflogin.actionactionunderthepathattributetofind,theActionServletreadstruts-config.xmlfiletofindaction,bythenameattributetofindthenameoftheform-beansform-beanpropertypackagenameoftheActionFormclassname,thefirstinstanceoftheform,filltheformvalues​​totheform,calltheform'svalidatemethodvalidation,theActionErrorsreturnnulltorepresentverificationthrough,orfailuretoreturntheinputspecifiedpage.verifiedbytheinstantiationaction,theimplementationoftheActionexecutemethod.

details

DisplayedinFigure6isastripped-downUMLdiagramoftheorg.apache.struts.actionpackage.Figure6showstheminimalrelationshipsamongActionServlet（Controller）,ActionForm（FormState）,andAction（ModelWrapper）.

Figure6.UMLdiagramoftherelationshipoftheCommand（ActionServlet）totheModel（Action&ActionForm）

TheActionServletclass

Doyourememberthedaysoffunctionmappings?

Youwouldmapsomeinputeventtoapointertoafunction.Ifyouwhereslick,youwouldplacetheconfigurationinformationintoafileandloadthefileatruntime.FunctionpointerarrayswerethegoodolddaysofstructuredprogramminginC.

LifeisbetternowthatwehaveJavatechnology,XML,J2EE,andallthat.TheStrutsControllerisaservletthatmapsevents（aneventgenerallybeinganHTTPpost）toclasses.Andguesswhat--theControllerusesaconfigurationfilesoyoudon_thavetohard-codethevalues.Lifechanges,butstaysthesame.

ActionServletistheCommandpartoftheMVCimplementationandisthecoreoftheFramework.ActionServlet（Command）createsandusesAction,anActionForm,andActionForward.Asmentionedearlier,thestruts-config.xmlfileconfigurestheCommand.DuringthecreationoftheWebproject,ActionandActionFormareextendedtosolvethespecificproblemspace.Thefilestruts-config.xmlinstructsActionServletonhowtousetheextendedclasses.Thereareseveraladvantagestothisapproach:

∙Theentirelogicalflowoftheapplicationisinahierarchicaltextfile.Thismakesiteasiertoviewandunderstand,especiallywithlargeapplications.

∙ThepagedesignerdoesnothavetowadethroughJavacodetounderstandtheflowoftheapplication.

∙TheJavadeveloperdoesnotneedtorecompilecodewhenmakingflowchanges.

CommandfunctionalitycanbeaddedbyextendingActionServlet.

TheActionFormclass

ActionFormmaintainsthesessionstatefortheWebapplication.ActionFormisanabstractclassthatissub-classedforeachinputformmodel.WhenIsayinputformmodel,IamsayingActio