SpringAOP simple guide.docx

SpringAOP simple guide.docx

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SpringAOPsimpleguide

SpringAOPSimpleGuide

AdrianZhong

Version1.0

July26,2011

HPConfidential

SimpleAOPIntroduction

Acommonobject-orientedtechniqueforreusingcommonfunctionalityistoapplyinheritanceordelegation.Butinheritancecanleadtoabrittleobjecthierarchyifthesamebaseclassisusedthroughoutanapplication,anddelegationcanbecumbersomebecausecomplicatedcallstothedelegateobjectmayberequired.

Concepts

SomeTerms

Advice

InAOPterms,thejobofanaspectiscalledadvice.

Joinpoint

Yourapplicationmayhaveaplentyofopportunitiesforadvicetobeapplied.Theseopportunitiesareknownasjoinpoints.

Pointcut

Anaspectdoesn’tnecessarilyadvisealljoinpointsinanapplication.Pointcutshelpnarrowdownthejoinpointsadvisedbyanaspect.

Aspect

Anaspectisthemergerofadviceandpointcuts.

Weaving

Weavingistheprocessofapplyingaspectstoatargetobjecttocreateanew,proxied

object.

InSpring,aspectsarewovenintoSpring-managedbeansatruntimebywrappingthemwithaproxyclass.

SpringAOPconfiguration

1.Commonspringproxybean

Thespringcontextfile

Configurationjustlikeothernon-proxybeans.TheinterceptorNamespropertytellsProxyFactoryBeanwhichadvisorstoapplytotheproxiedbean.ThisOnlyuncomfortableisthattherealtargetbeanisnottheonewegetwhenwewannauseandgetformthespringApplicationContext.（Inanotherword,theinjectionandtheusageisnottransparent）

Advice

TheadvicesorcalledinterceptorsshouldinheritedfromMethodBeforeAdvice,MethodAfterAdviceetc.

Thiskindadivceiseasytouse,somehowliketheJDKDynamicProxy’sInvocationHandler.

2.AOPtagproxybean

Thespringcontextfile

Moreeasier,butneedtoaddtheAOPtagschema.Well,that’snotthecase.Exciting,theusageoftheapplicationfinallybecometransparenttothedevelopernow!

（Ifyouwanttoknowmoreaboutthepointcutconfigurationblew,pleasereferencetotheAspectJtoseemoreinfo）

Advice

PurePOJO,feelsgood~

3.Aopannotation

Thespringcontextfile

Thesimplest,easiest…whatcanweexpectmore…

Aspect

AnnotationedPOJOAOPtagproxybeanxmlconfiguration,butmappingthepointcutsandtheadvicesusingtheannotation.

Other

Weavingtime

Asmentionabove,weavingtimecouldbedifferentthroughtheobject’slifetime.

1.CompileTime

Itworkswhencompiletheclass,itneedaspecialcompilewhichcouldmergetheAspectintotheclassfiledirectlyduringthecompiletime.

Example:

AspectJ

2.ApplicationRuntime

Thiscansimplydividedintotwophases.Classloadingtimeandtheprogramruntime.

Example:

Spring（runtime）,AspectJ（specialClassLoader）

ProxiedClasses

Springgeneratesproxiedclassesintwoways.

1.JDKDynamicProxy

2.CGLIB

Ifyourtargetobjectimplementsaninterface（s）thatexposestherequiredmethods,SpringwillusetheJDK’sjava.lang.reflect.Proxyclass.ThisclassallowsSpringtodynamicallygenerateanewclassthatimplementsthenecessaryinterfaces,weaveinanyadvice,andproxyanycallstotheseinterfacestoyourtargetclass.Ifyourtargetclassdoesnotimplementaninterface,SpringusestheCGLIBlibrarytogenerateasubclasstoyourtargetclass.

■Creatingaproxywithinterfacesisfavoredoverproxyingclasses,sincethisleadstoamorelooselycoupledapplication.Theabilitytoproxyclassesisprovidedsothatlegacyorthird-partyclassesthatdonotimplementinterfacescanstillbeadvised.Thisapproachshouldbetakenastheexception,nottherule.

■Methodsmarkedasfinalcannotbeadvised.Remember,Springgeneratesasubclasstoyourtargetclass.Anymethodthatneedstobeadvisedisoverriddenandadviceiswovenin.Thisisnotpossiblewithfinalmethods.

Nowletusjustlookattheproxiedclassgeneratedbythecontext.（Ijustcannotgetthebytestreamoftheproxiedclasses,sothearticlesbelowisjustmypersonalconsideration.Ifthereisanywrong,pleasepleaseletmeknow.）

BeginwiththeJDKDynamicProxyclass.

JDKDynamicProxyClass

Youmustnotifiedthattherearelotsofstaticclassmemberwithmeaninglessname,forpersonal,thesemarkscouldbeusedtomarkthespecificmethod,usedwhentheproxiedmethodiscalled.

GuessImplementation

AnotherCGLIBclass.

CGLIBProxyClass

Attachedthecodeofthesetests.

References

1.<>2nd.Edition.Aug.2007

2.<>