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(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
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