设计模式案例（一）

DesignPatterns,ArchitecturalPatternsPascalMolliUniversityHenri-PoincaréPascal.Molli@loria.fr1Bibliography…«

ASystemofPattern

»BushmannetAll«

DesignPatterns

»GammaetAll«

ConcurrentProgramminginJava

»D.Lea.«

DistributedObjects

»OrfalietAll«

ApplyingUMLandPatterns

»Larman2Patterns…«

Patternshelpyoubuildonthecollectiveexperienceofskilledsoftwareengineers.

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Theycaptureexisting,well-provenexperienceinsoftwaredevelopmentandhelptopromotegooddesignpractice

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Everypatterndealswithaspecific,recurringprobleminthedesignorimplementationofasoftwaresystem

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Patternscanbeusedtoconstructsoftwarearchitectureswithspecificproperties…

»3BecomingaChessMasterFirstlearnrulesandphysicalrequirementse.g.,namesofpieces,legalmovements,chessboardgeometryandorientation,etc.

Thenlearnprinciplese.g.,relativevalueofcertainpieces,strategicvalueofcentersquares,powerofathreat,etc.

However,tobecomeamasterofchess,onemuststudythegamesofothermastersThesegamescontainpatternsthatmustbeunderstood,memorized,andappliedrepeatedlyTherearehundredsofthesepatterns4BecomingaSoftwareDesignerMasterFirstlearntherulese.g.,thealgorithms,datastructuresandlanguagesofsoftware

Thenlearntheprinciplese.g.,structuredprogramming,modularprogramming,objectorientedprogramming,genericprogramming,etc.

However,totrulymastersoftwaredesign,onemuststudythedesignsofothermastersThesedesignscontainpatternsmustbeunderstood,memorized,andappliedrepeatedlyTherearehundredsofthesepatterns5SoftwareArchitectureAsoftwarearchitectureisadescriptionofthesubsystemsandcomponentsofasoftwaresystemandtherelationshipsbetweenthem.

Subsystemsandcomponentsaretypicallyspecifiedindifferentviewstoshowtherelevantfunctionalandnon-functionalpropertiesofasoftwaresystem.

Thesoftwaresystemisanartifact.Itistheresultofthesoftwaredesignactivity.6ComponentAcomponentisanencapsulatedpartofasoftwaresystem.Acomponenthasaninterface.Componentsserveasthebuildingblocksforthestructureofasystem.

Ataprogramming-languagelevel,componentsmayberepresentedasmodules,classes,objectsorasetrelatedfunctions.7SubsystemsAsubsystemisasetofcollaboratingcomponentsperformingagiventask.Asubsystemisconsideredaseparateentitywithinasoftwarearchitecture.

Itperformsitsdesignatedtaskbyinteractingwithothersubsystemsandcomponents…8ArchitecturalPatterns AnarchitecturalPatternexpressafundamentalstructuralorganizationschemaforsoftwaresystems.Itprovidesasetofpredefinedsubsystems,theirresponsibilities,andincludesrulesandguidelinesfororganizingtherelationshipsbetweenthem.9Designpatterns Adesignpatternprovidesaschemeforrefiningthesubsystemsorcomponentsofasoftwaresystem,ortherelationshipsbetweenthem.Itdescribesacommonly-recurringstructureofcommunicatingcomponentsthatsolvesageneraldesignproblemwithinaparticularcontext.10Idioms AnIdiomisalow-levelpatternspecifictoaprogramminglanguage.Anidiomdescribeshowtoimplementparticularaspectsofcomponentsortherelationshipsbetweenthemusingthefeaturesofthegivenlanguage.11Framework Aframeworkisapartiallycompletesoftware(sub-)systemthatisintendedtobeinstantiated.Itdefinesthearchitectureforafamilyof(sub-)systemsandprovidesthebasicbuildingblockstocreatethem.Italsodefinestheplaceswhereadaptationsforspecificfunctionalityshouldbemade.12FirstExampleADiceGameAPlayerrolls10x2dicesIfresult=7,score=score+10pointsAttheend,scoreoftheplayerisregistredinthehighscoretable.13menuviewHighscoreStartturn=0RollDiceturn++UpdatehighscoreTurn<10[highscore][start][exit][true][false]ActivityDiagram14AnalysisDiagram…15DesignStageManageUserInterfaceManagePersistenceofhighscoreinafileorinrelationaldatabaseRealizeanlayeredarchitecture:ApplytheLayerArchitecturalPattern16Layerhelpstostructureapplicationthatcanbedecomposedintogroupsofsubtasksinwhicheachgroupofsubtasksisataparticularlevelofabstraction.17Layer:examples18Layer:Structure19Layer:Structure20Layerandcomponents…21Layers:VariantsRelaxedLayeredSystem:Alayer«

j

»canuseserviceofj-1,j-2…AlayercanbepartiallyopaqueSomeservicetolayerj+1,otherstoallupperservices…Layeringthroughinheritance:LowerlayersareimplementedasbaseclassesHigherlevelcanoverridelowerlevel…22Layers:KnownUsesVirtualmachines:JVMandbinarycodeformatAPI:LayerthatencapsulateslowerlayersInformationSystemPresentation,Applicationlogic,DomainLayer,DatabaseWindowsNT(relaxedfor:kernelandIOandhardware)Systemservices,Resourcemanagement(Objectmanager,securitymonitor,processmanager,I/Omanager,VMmanager,LPC),Kernel(exceptionhandling,interrupt,multiprosynchro,threads),HAL(HardwareAbstractionLevel)Hardware23Layers:benefitsReuseoflayersSupportforstandardization(POSIX)DependenciesarekeptlocalExchangeabilities:ReplacementofoldimplementationwithAdapterPatternDynamicexchangewithBridgePattern24Layers:LiabilitiesCascadesofchangingbehaviorLowerefficiencyUnnecessarywork:functionsofalayercalledmanytimesforoneserviceDifficultyofestablishingcorrectgranularityoflayers:Tofewlayer->lessbenefits,tomuchlayer->complexityandoverhead…25ApplyingLayerArchitecturePlayViewHighScoreFichierouBDDUICorePersistence26Package

decompositionUI<<layer>>Core<<layer>>Persist<<layer>>Util<<subsystem>>27Layer«

core

»Containbusinesslogicclasses…AdaptanalysisclassesforimplementationUseofsingletonIdiom…28Singleton(Idiom)Ensureaclassonlyhasoneinstance,andprovideaglobalpointofaccesstoit.29SingletonStructure30Core«

Layer

»:1erdiagrammeDesignAnalyse31Package

decompositionUI<<layer>>Core<<layer>>Persist<<layer>>Util<<subsystem>>32ObserverOne-to-manydependencybetweenobjects:changeofoneobjectwillautomaticallynotifyobservers33Observer:ApplicabilityAchangetooneobjectrequireschanginganunknownsetofothersObjectshouldbeabletonotifyothersthatmaynotbeknownatthebeginning34Observer:Structure35Observer:ConsequencesAbstractcouplingbetweensubjectandobserverSupportforbroadcastcommunicationHardtomaintain36ApplyingObserverPattern37ObserverView38Viewsaregraphicalobjects39SettingupObserver40Observer:ChangePropagation:Die:Randomizer:DieView1:getValue()2:setValue(int)3:notifyObservers()4:update(Observable,Object)5:getState()3:JLabel6:setText(3)41Architectureencouche...UICoreDecouplingclassesandinterfaces42Package

decompositionUI<<layer>>Core<<layer>>Persist<<layer>>Util<<subsystem>>43PatternFactoryMethodIntentDefineaninterfaceforcreatinganobject,butletsub-classesdecidewhichclasstoinstantiateletaclassdeferinstantiationtosubclassesAlsoknownasVirtualConstructor44FactoryMethod Applicability:Usewhenaclasscannotanticipatetheclassofobjectsitmustcreateaclasswantsitssubclassestospecifytheobjectsitcreatesclassesdelegateresponsibilitytooneofseveralhelpersubclasses,andyouwanttolocalizetheknowledgeofwhichhelpersubclasstodelegate.45Structure46FactorymethodConsequencesProvidehooksforsubclassesconnectsparallelclasshierarchiesKnownusesMacApp,ET++ClassViewinsmalltalk80MVC(controllercreation)OrbixORBforgeneratingPROXYobject47Layer«

Persist

»ClassestechniquesdepersistancesAssurerl

’indépendanceCore/Persistpouvoirchangerde«

persistentengine

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Sérialisation

»Persistanceviaunebasededonnéesrelationnelle(JDBC).48ApplyingFactoryProduitabstraitFabriqueabstraiteProduitconcretFabriqueconcrête49ApplyingFactory50Summary1Architecturalpattern:Layer2DesignPatterns:Observer,Factory1Idiom:SingletonPb:Combiningpatterntocombinetheirforces…5152

Bankexample…Abasicbanksystem:1bank,nAccount.

Eachaccountbelongto1client.Eachaccountiscreditedbyanamountamoney.BankfunctionsWithdrawalonaaccount,Creditanaccount,Transfermoneyfromoneaccounttoanother…53Naivesolution54NaiveSolution55ApplyingCommandPattern…Encapsulatearequestasanobject,therebylettingyouparameterizeclientswithdifferentrequests,queueorlogrequests,andsupportundoableoperations.56CommandExample57CommandExample58CommandStructure59CommandStructure60CommandConsequencesCommanddecouplestheobjectthatinvokestheoperationfromtheonethatknowshowtoperformit.Commandsarefirst-classobjects.Theycanbemanipulatedandextendedlikeanyotherobject.

It'seasytoaddnewCommands,becauseyoudon'thavetochangeexistingclasses.61ApplyingCommandPattern62ApplyingCommandPattern63CompositePatternComposeobjectsintotreestructurestorepresentpart-wholehierarchies.Compositeletsclientstreatindividualobjectsandcompositionsofobjectsuniformly.64CompositeExample65CompositeExample66CompositeStructure67ApplyingCompositeonCommand68ApplyingComposite6970ApplyingSingleton71AndSoon…Storingstate:MementoPatternObservingAccount:ObserverPatternVisitingallobjectgraph:VisitorPatternRemoteaccess:Proxypattern…72ProxyPatternProvideasurrogateorplaceholderforanotherobjecttocontrolaccesstoit.73ProxyExample74ProxyStructure75Proxybenefitsremoteproxycanhidethefactthatanobjectresidesinadifferentaddressspace.Avirtualproxycanperformoptimizationssuchascreatinganobjectondemand.

Bothprotectionproxiesandsmartreferencesallowadditionalhousekeepingtaskswhenanobjectisaccessed.76From«

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»Gamma&Al77AdapterPatternConverttheinterfaceofaclassintoanotherinterfaceclientsexpect.Adapterletsclassesworktogetherthatcouldn'totherwisebecauseofincompatibleinterfaces.78AdapterExample79AdapterStructure80VisitorPatternRepresentanoperationtobeperformedontheelementsofanobjectstructure.Visitorletsyoudefineanewoperationwithoutchangingtheclassesoftheelementsonwhichitoperates.81Visitorexample82Visitorexample83Visitorapplicabilitymanydistinctandunrelatedoperationsneedtobeperformedonobjectsinanobjectstructure,andyouwanttoavoid"polluting"theirclasseswiththeseoperations84VisitorStructure85VisitorStructure86VisitorConsequencesVisitormakesaddingnewoperationseasyAvisitorgathersrelatedoperationsandseparatesunrelatedonesAddingnewConcreteElementclassesishardVisitingacrossclasshierarchiesAccumulatingstate.Breakingencapsulation87ChainofresponsabilityAvoidcouplingthesenderofarequesttoitsreceiverbygivingmorethanoneobjectachancetohandletherequest.Chainthereceivingobjectsandpasstherequestalongthechainuntilanobjecthandlesit.88

89ChainofResponsability90Chainofresponsability91ParticipantsHandler(HelpHandler) definesaninterfaceforhandlingrequests.(optional)implementsthesuccessorlink.ConcreteHandler(PrintButton,PrintDialog)handlesrequestsitisresponsiblefor.canaccessitssuccessor.iftheConcreteHandlercanhandletherequest,itdoesso;otherwiseitforwardstherequesttoitssuccessor.Client

initiatestherequesttoaConcreteHandlerobjectonthechain.92Example…Awt1.0From«

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»Gamma&Al93StrategyDefineafamilyofalgorithms,encapsulateeachone,andmaketheminterchangeable.Strategyletsthealgorithmvaryindependentlyfromclientsthatuseit.94Strategy…95Strategy96ParticipantsStrategy(Compositor)declaresaninterfacecommontoallsupportedalgorithms.ContextusesthisinterfacetocallthealgorithmdefinedbyaConcreteStrategy.ConcreteStrategy(SimpleCompositor,TeXCompositor,ArrayCompositor)implementsthealgorithmusingtheStrategyinterface.Context(Composition)isconfiguredwithaConcreteStrategyobject.maintainsareferencetoaStrategyobject.maydefineaninterfacethatletsStrategyaccessitsdata.97Strategy…From«

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»Gamma&Al98StateAllowanobjecttoalteritsbehaviorwhenitsinternalstatechanges.Theobjectwillappeartochangeitsclass.From«

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»Gamma&Al99ExempleFrom«

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»Gamma&Al101ConsequencesItlocalizesstate-specificbehaviorandpartitionsbehaviorfordifferentstatesItmakesstatetransitionsexplicitStateobjectscanbesharedFrom«

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»Gamma&Al102DecoratorAttachadditionalresponsibilitiestoanobjectdynamically.Decoratorsprovideaflexiblealternativetosubclassingforextendingfunctionality.From«

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»Gamma&Al107Applicabilitytoaddresponsibilitiestoindividualobjectsdynamicallyandtransparently,thatis,withoutaffectingotherobjects.forresponsibilitiesthatcanbewithdrawnwhenextensionbysubclassingisimpracticalFrom«

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»Gamma&Al108ConsequencesMoreflexibilitythanstaticinheritanceAvoidsfeature-ladenclasseshighupinthehierarchyAdecoratoranditscomponentaren'tidenticalLotsoflittleobjectsFrom«

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»Gamma&Al110BridgeDecoupleanabstractionfromitsimplementationsothatthetwocanvaryindependently.From«

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»Gamma&Al114BridgeDecouplinginterfaceandimplementationImprovedextensibilityHidingimplementationdetailsfromclientsFrom«

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»Gamma&Al117BuilderSeparatetheconstructionofacomplexobjectfromitsrepresentationsothatthesameconstructionprocesscancreatedifferentrepresentations.From«

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»Gamma&Al121BuilderConsequencesItletsyouvaryaproduct'sinternalrepresentationItisolatescodeforconstructionandrepresentationItgivesyoufinercontrolovertheconstructionprocessFrom«

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»Gamma&Al122FlyWeightUsesharingtosupportlargenumbersoffine-grainedobjectsefficiently.From«

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»Gamma&Al127Flyweight:ApplicabilitéEtatintrinsèque/extrinsèque…Lesétatsextrinsèquespeuventêtrecalculés…From«

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»Gamma&Al129IteratorProvideawaytoaccesstheelementsofanaggregateobjectsequentiallywithoutexposingitsunderlyingrepresentationFrom«

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»Gamma&Al133MementoWithoutviolatingencapsulation,captureandexternalizeanobject'sinternalstatesothattheobjectcanberestoredtothisstatelater.From«

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»Gamma&Al134MementoStructure…From«

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»Gamma&Al135Memento…PreservingencapsulationboundariesItsimplifiesOriginatorUsingmementosmightbeexpensive.DefiningnarrowandwideinterfacesHiddencostsincaringformementosFrom«

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»Gamma&Al137Designproblems…Documentstructure.ThechoiceofinternalrepresentationforthedocumentaffectsnearlyeveryaspectofLexi'sdesign.Allediting,formatting,displaying,andtextualanalysiswillrequiretraversingtherepresentation.Thewayweorganizethisinformationwillimpactthedesignoftherestoftheapplication.

Formatting.HowdoesLexiactuallyarrangetextandgraphicsintolinesandcolumns?Whatobjectsareresponsibleforcarryingoutdifferentformattingpolicies?Howdothesepoliciesinteractwiththedocument'sinternalrepresentation?

From«

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»Gamma&Al138Designproblems…Embellishingtheuserinterface.Lexi'suserinterfaceincludesscrollbars,borders,anddropshadowsthatembellishtheWYSIWYGdocumentinterface.SuchembellishmentsarelikelytochangeasLexi'suserinterfaceevolves.Henceit'simportanttobeabletoaddandremoveembellishmentseasilywithoutaffectingtherestoftheapplication.

Supportingmultiplelook-and-feelstandards.Lexishouldadapteasilytodifferentlook-and-feelstandardssuchasMotifandPresentationManager(PM)withoutmajormodification.From«

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»Gamma&Al139Designproblems…Embellishingtheuserinterface.Lexi'suserinterfaceincludesscrollbars,borders,anddropshadowsthatembellishtheWYSIWYGdocumentinterface.SuchembellishmentsarelikelytochangeasLexi'suserinterfaceevolves.Henceit'simportanttobeabletoaddandremoveembellishmentseasilywithoutaffectingtherestoftheapplication.

Supportingmultiplelook-and-feelstandards.Lexishouldadapteasilytodifferentlook-and-feelstandardssuchasMotifandPresentationManager(PM)withoutmajormodification.From«

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»Gamma&Al140Designproblems…Spellingcheckingandhyphenation.HowdoesLexisupportanalyticaloperationssuchascheckingformisspelledwordsanddetermininghyphenationpoints?Howcanweminimizethenumberofclasseswehavetomodifytoaddanewanalyticaloperation?From«

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»Gamma&Al157Summary(C.Alexander)Itispossibletomakebuildingbystringingtogetherpatterns,inaratherlooseway.Abuildingmadelikethis,isanassemblyofpatterns.Itisnotdense.Itisnotprofound.Butitisalsopossibletoputpatternstogetherinsuchwaythatmanypatternsoverlapinthesamephysicalspace:thebuildingisverydense;ithasmanymeaningscapturedinasmallspace;andthroughthisdensity,itbecomesprofound.158ArchitecturalPatterns…FromMUDtoStructure…Layers,PipeandFilters,BlackboardDistributedSystems…Broker,PipeandFilters,MicrokernelInteractiveSystems…MVC,PACAdaptableSystems…Microkernel,Reflection…159Layerhelpstostructureapplicationthatcanbedecomposedintogroupsofsubtasksinwhicheachgroupofsubtasksisataparticularlevelofabstraction.160Layer:examples161Layer:Structure162Layer:Structure163Layerandcomponents…164LayerandFacadeDP…165LayerandFacadeDP166Layers:VariantsRelaxedLayeredSystem:Alayer«

j

»canuseserviceofj-1,j-2…AlayercanbepartiallyopaqueSomeservicetolayerj+1,otherstoallupperservices…Layeringthroughinheritance:LowerlayersareimplementedasbaseclassesHigherlevelcanoverridelowerlevel…167Layers:KnownUsesVirtualmachines:JVMandbinarycodeformatAPI:LayerthatencapsulateslowerlayersInformationSystemPresentation,Applicationlogic,DomainLayer,DatabaseWindowsNT(relaxedfor:kernelandIOandhardware)Systemservices,Resourcemanagement(Objectmanager,securitymonitor,processmanager,I/Omanager,VMmanager,LPC),Kernel(exceptionhandling,interrupt,multiprosynchro,threads),HAL(HardwareAbstractionLevel)Hardware168Layers:benefitsReuseoflayersSupportforstandardization(POSIX)DependenciesarekeptlocalExchangeabilities:ReplacementofoldimplementationwithAdapterPatternDynamicexchangewithBridgePattern169Layers:LiabilitiesCascadesofchangingbehaviorLowerefficiencyUnnecessarywork:functionsofalayercalledmanytimesforoneserviceDifficultyofestablishingcorrectgranularityoflayers:Tofewlayer->lessbenefits,tomuchlayer->complexityandoverhead…170PipesandFiltersProvidesastructureforsystemsthatprocessastreamofData.Eachprocessingstepisencapsulatedinafiltercomponent.Dataispassedthroughpipesbetweenadjacentfilters.Recombiningfiltersallowstobuildfamiliesofrelatedsystems.171PipesandFilters:Example172PipesandFilters:Structure173PipesandFilters174PipesandFilters:pushpipeline175PipesandFilters:pullpipeline176PipesandFilters:push-pullpipeline177PipesandFilters:ThreadedFilters178PipesandFilters:KnownUsesUnixCMSPipelines(extensionIBMmainframes)LASSPTools(NumericalAnalysis)Graphicalinputdevices(knobsorsliders)FiltersfornumericalanalysisanddataextractionDatasinkstoproduceanimationfromnumericaldatastreams…Khoros:Imagerecognition…WEB!!Servlet!!179PipesandFiltersbenefitsNointermediatefilenecessary(butpossible)FlexibilitybyfilterexchangeFlexibilitybyrecombinationReuseoffiltercomponentsRapidprototypingofpipelineEfficiencybyparallelprocessing180PipesandFiltersLiabilitiesSharingstateinformationisexpensiveorinflexibleEfficiencygainbyparallelprocessingisoftenanillusion

Costofdatatransfer,filtersthatconsumealldatabeforeoneoutput,contextswitchononecomputer,synchronizationoffiltersviapipesDatatransformationoverheadErrorHandling181[SunDeveloppers]From«

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»Gamma&Al183Blackboard TheBlackboardarchitecturalpatternisusefulforproblemsforwhichnodeterministicsolutionstrategiesareknown.Severalspecializedsubsystemsassembletheirknowledgetobuildapossiblypartialorapproximatesolution.184BlackboardExample185BlackboardStructure186BlackboardStructure187BlackboardStructure188BlackboardVariantsProductionSystem(OPSLanguage)Blackboard:workingmemoryKnowledgesource:Condition-actionrulesControl:conflictresolutionmodule.

Repository:

blackboard:Data,