(面向?qū)ο笤O(shè)計)Part6Aspect Oriented Programming

(面向?qū)ο笤O(shè)計)Part6AspectOrientedProgrammingExample-FigureEditorAfigureconsistsofseveralfigureelements.Afigureelementiseitherapointoraline.FiguresaredrawnonDisplay.ApointincludesXandYcoordinates.Alineisdefinedastwopoints.Example-FigureEditor-DesignDisplayFigureFigureElement*PointLinegetX()getY()getP1setP1setX(int)setY(int)setP1(Point)setP2(Point)2ComponentsareCohesiveLooselyCoupledHavewell-definedinterfaces

(abstraction,encapsulation)CrosscuttingConcern-ExampleDisplayFigureFigureElement*PointLinegetX()getY()getP1setP1DisplayTrackingsetX(int)setY(int)setP1(Point)setP2(Point)2NotifyScreenManagerifafigureelementmovesclassPoint{voidsetX(intx){_x=x;}}classTracer{

staticvoidtraceEntry(Stringstr)

{ System.out.println(str);}staticvoidtraceExit(Stringstr)

{ System.out.println(str);

}}DisplayFigureFigureElement*PointLinegetX()getY()getP1setP1setX(int)setY(int)setP1(Point)setP2(Point)2Tracer

Tracer.traceEntry(“EntryPoint.set”);Tracer.traceExit(“ExitPoint.set”);classLine{voidsetP1(Pointp1{_p1=p1;}}

Tracer.traceEntry(“EntryLine.set”);Tracer.traceExit(“ExitLine.set”);TanglingCodeExample-TracingScatteredConcernCrosscuttingConcernsConcernsthatnaturallytendtobescatteredovermultiplecomponentsConnotbelocalizedintosingleunitscomponents,objects,procedures,functionsIfnotappropriatelycopedwith:ScatteredovermultiplecomponentsTangledcodepercomponentCrosscutting,ScatteringandTanglingCrosscuttingConcernthatinherentlyrelatestomultiplecomponentsResultsinscatteredconcernandtangledcodeScatteringSingleconcernaffectsmultiplemodulesTanglingMultipleconcernsareinterleavedinasinglemoduleTheCostofCrosscuttingConcernsReducedunderstandabilityRedundantcodeinmanyplacesNon-explicitstructureDecreasedadaptabilityHavetofindallthecodeinvolvedHavetobesuretochangeitconsistentlyHavetobesurenottobreakitbyaccidentNewconcernscannotbeeasilyaddedDecreasedreusabilityComponentcodeistangledwithspecifictanglingcodeDecreasedmaintainability‘Rippleeffect’ExampleofCrosscuttingConcernsSynchronizationReal-timeconstraintsError-checkingObjectinteractionconstraintsMemorymanagementPersistencySecurityCachingLoggingMonitoringTestingDomainspecificoptimization...ManycrosscuttingconcernsmayappearinonesystemExample:DistributedSystemDesignComponentinteractionSynchronizationRemoteinvocationLoadbalancingReplicationFailurehandlingQualityofserviceDistributedtransactionsWhattoDo...?HistoricalContextCrosscuttingconcernsarenewtypeofconcernsthathavenotbeen(appropriately)detected/handledbefore.NoexplicitmanagementuntilrecentlyatprogramminglevelNoexplicitconsiderationindesignmethodsNoexplicitconsiderationinprocessNoexplicitconsiderationincasetoolsAspect-OrientedSoftwareDevelopmentProvidesbetterseparationofconcernsbyexplicitlyconsideringcrosscuttingconcerns(aswell)Doesthisbyprovidingexplicitabstractionsforrepresentingcrosscuttingconcerns,i.e.aspectsAndcomposingtheseintoprograms,i.e.aspectweavingoraspectcomposing.AssuchAOSDimprovesmodularityAndsupportsqualityfactorssuchasMaintainability,Adaptability,Reusability,Understandability...ImpactofAOSDonSociety...MITTechnologyReviewlistsAOPasoneofthetop10emergingtechnologiesthatwillchangetheworld–(MITTechnologyReview,January2001)

BasicAOSDTechnologiesCompositionFilters(since1991)UniversityofTwente,TheNetherlandsAspectJ(since1997)XEROXPARC,USDemeterJ/DJ(1993)NortheasternUniversity,USMulti-dimensionalseparationofConcerns/HyperJ(1999)JBossAOPSupportedinJBossAS5AspectJAgeneralpurposeAOprogramminglanguagejustasJavaisageneral-purposeOOlanguageAnintegratedextensiontoJavaacceptsalljavaprogramsasinputoutputs.classfilescompatiblewithanyJVMintegratedwithtoolshttp:///aspectj/classLine{

privatePoint_p1,_p2;PointgetP1(){return_p1;}PointgetP2(){return_p2;}

voidsetP1(Pointp1){

Tracer.traceEntry(“entrysetP1”);_p1=p1;Tracer.traceExit(“exitsetP1”);}

voidsetP2(Pointp2){

Tracer.traceEntry(“entrysetP2”);_p2=p2;Tracer.traceExit(“exitsetP2”);}classPoint{

private

int_x=0,_y=0;

intgetX(){return_x;}

intgetY(){return_y;}

voidsetX(intx){Tracer.traceEntry(“entrysetX”);_x=x;Tracer.traceExit(“exitsetX”)}

voidsetY(inty){Tracer.traceEntry(“exitsetY”);_y=y;Tracer.traceExit(“exitsetY”);}}Example–WithoutAOPTanglingCodeScatteredConcernclassTracer{

staticvoidtraceEntry(Stringstr)

{ System.out.println(str);}

staticvoidtraceExit(Stringstr)

{ System.out.println(str);

}}classLine{

privatePoint_p1,_p2;PointgetP1(){return_p1;}PointgetP2(){return_p2;}

voidsetP1(Pointp1){_p1=p1;}

voidsetP2(Pointp2){_p2=p2;}}classPoint{

private

int_x=0,_y=0;

intgetX(){return_x;}

intgetY(){return_y;}

voidsetX(intx){_x=x;}

voidsetY(inty){_y=y;}}Example–WithAOPaspect

Tracing{

pointcuttraced():call(*Line.*||call(*Point.*);before():traced(){println(“Entering:”+

thisjopinpoint);

void

println(Stringstr){<writetoappropriatestream>}}}AspectisdefinedinaseparatemoduleCrosscuttingislocalizedNoscattering;NotanglingImprovedmodularityAspectLanguageElementsJoinPoint(JP)modelcertainprincipledpointsinprogramexecution

suchasmethodcalls,fieldaccesses,andobjectconstructionMeansofidentifyingJPspickingoutjoinpointsofinterest(predicate)pointcuts:setofjoinpointsMeansofspecifyingbehavioratJPswhathappensadvicedeclarationstheadditionalcodethatyouwanttoapplytoyourexistingmodel.JoinpointsmethodcalljoinpointswhenamethodiscalledmethodreceptionjoinpointswhenanobjectreceivesamessagemethodexecutionjoinpointswhenthebodyofcodeforanactualmethodexecutesfieldgetjointpointwhenafieldisaccessedfieldsetjointpointwhenafieldissetexceptionhandlerexecutionjoinpointwhenanexceptionhandlerexecutesobjectcreationjoinpointwhenaninstanceofaclassiscreatedSomeprimitivepointcutscall(Signature)picksoutmethodorconstructorcallbasedonSignatureexecution(Signature)picksoutamethodorconstructorexecutionjoinpointbasedonSignatureget(Signature)picksoutafieldgetjoinpointbasedonSignatureset(Signature)picksoutafieldsetjoinpointbasedonSignaturehandles(TypePattern)picksoutanexceptionhandlerofanyoftheThrowabletypesofTypePatterninstanceOf(ClassName)picksoutjoinpointsofcurrentlyexecutingobjectsofclassClassNamewithin(ClassName)picksoutjoinpointsthatareincodecontainedinClassNamewithinCode(Signature)picksoutjoinpointswithinthememberdefinedbymethororconstructor(Signature)cflow(pointcut)picksoutallthejoinpointsinthecontrolflowofthejoinpointspickedoutbythepointcutAdvicePieceofcodethatattachestoapointcutandthusinjectsbehavioratalljoinpointsselectedbythatpointcut.example:before(args):pointcut

{Body}wherebeforerepresentsabeforeadvicetype(seenextslide).CantakeparameterswithpointcutsAdviceTypesAdvicecodeexecutesbefore,codeisinjectedbeforethejoinpointbefore(args):pointcut

{Body}after,codeisinjectedafterthejoinpoint

after(args):pointcut

{Body}around,codeisinjectedaround(inplaceof)codefromjoinpointReturnTypearound(args):pointcut

{Body}JPAdviceJPAdviceAdviceJPAspectAmodularunitofcross-cuttingbehavior.Likeaclass,canhavemethods,fields,initializers.canbeabstract,inheritfromclassesandabstractaspectsandimplementinterfaces.encapsulatespointcutsandadvicescanintroducenewmethods/fieldstoaclassAspectXAspectYclassXAspectYAspectXclassYxclassLine{

privatePoint_p1,_p2;PointgetP1(){return_p1;}PointgetP2(){return_p2;}

voidsetP1(Pointp1){_p1=p1;}

voidsetP2(Pointp2){_p2=p2;}}classPoint{

private

int_x=0,_y=0;

intgetX(){return_x;}

intgetY(){return_y;}

voidsetX(intx){_x=x;}

voidsetY(inty){_y=y;}}Example-AspectJaspect

Tracing{pointcuttraced():call(*Line.*||call(*Point.*);before():traced(){println(“Entering:”+

thisjopinpoint);

after():traced(){println(“Exit:”+

thisjopinpoint);

void

println(St