spring源代码之详解.doc

上一章当中我没有提及具体的搭建环境的步骤，一个是不得不承认有点懒，另外一个我觉得如果上章所述的那些环境都还不会搭建的话，研究spring的源码还有些过早。如果你有兴趣的话，相信已经搭建好了学习研究的环境，接下来就可以进入正题了。网上也有很多关于spring源码学习的文章以及帖子，讲的也都不错，但是有些可能高估了读者的能力，该深入的地方反倒一句带过，我现在也是在一步一步研究，和大家的进度一样，所以可能在我的角度来和各位探讨，更加容易。首先我们来说一下IOC，IOC是spring最核心的理念，包括AOP也要屈居第二，那么IOC到底是什么呢，四个字，控制反转。网上有不少是这么解释IOC的，说IOC是将对象的创建和依赖关系交给容器，这句话我相信不少人都知道，在我个人的理解，IOC就是让我们的开发变的更简单了。为什么这么说呢，光说没意思，直接上代码。publicclassPersonpublicvoidwork()System.out.println(Iamworking);上面这个是Person类，如果我们还有一个Company公司类，公司要开张需要人来工作，所以我们可能需要这样。publicclassCompanypublicPersonperson; publicCompany(Personperson)this.person=person;publicvoidopen()person.work();System.out.println(Iamopening);好了，这样可以了，虽说和现实有些区别，毕竟没有一个人的公司，但是就是这么个意思。必须要有人在公司里，公司才能开张。有了spring上述情况我们是怎么写的呢？Person类不变，Company就可以简单些了。publicclassCompanyAutowiredpublicPersonperson;publicvoidopen()person.work();System.out.println(Iamopening);OK了，使用注解后，spring里的写法是这样的，是不是简单很多？或许你可能会说，这才减少了多少代码，但是事实上是，真正的项目中，不可能有这么简单的依赖关系，或许是2层，3层甚至N层。当然，可能我们有时候用的XML，XML和注解的区别就在于这里，注解可以快速的完成依赖的注入，但是缺点也很明显，那就是比如我公司里不需要人了，我需要的是机器，那么我还要手动改代码，将Person换成机器（这里应该是英文，英语不好，懒得查了 dadiao 缪买网，只记得念“磨洗”），而如果是XML配置，那么我们只需要改下配置文件就可以。维护起来会方便很多，当然XML的缺点也很明显，那就是依赖关系复杂的时候，XML文件会比较臃肿，所以我们一般的做法是将XML分离开来。说到这里，有些扯远了，但是我觉得以上可以足够说明IOC的好处，知道了IOC的好处，我们自然就要知道怎么来实现IOC了。或许看了spring的源码，第一感觉是很蒙，包太多，我也很蒙，但是研究东西就是得沉下心来，先来关注一下这个接口，BeanFactory，附上代码。/*Copyright2002-2010theoriginalauthororauthors.*LicensedundertheApacheLicense,Version2.0(theLicense);*youmaynotusethisfileexceptincompliancewiththeLicense.*YoumayobtainacopyoftheLicenseat*/licenses/LICENSE-2.0*Unlessrequiredbyapplicablelaworagreedtoinwriting,software*distributedundertheLicenseisdistributedonanASISBASIS,*WITHOUTWARRANTIESORCONDITIONSOFANYKIND,eitherexpressorimplied.*SeetheLicenseforthespecificlanguagegoverningpermissionsand*limitationsundertheLicense.*/packageorg.springframework.beans.factory;importorg.springframework.beans.BeansException;/*TherootinterfaceforaccessingaSpringbeancontainer.*Thisisthebasicclientviewofabeancontainer;*furtherinterfacessuchaslinkListableBeanFactoryand*linkorg.springframework.beans.factory.config.ConfigurableBeanFactory*areavailableforspecificpurposes.*Thisinterfaceisimplementedbyobjectsthatholdanumberofbeandefinitions,*eachuniquelyidentifiedbyaStringname.Dependingonthebeandefinition,*thefactorywillreturneitheranindependentinstanceofacontainedobject*(thePrototypedesignpattern),orasinglesharedinstance(asuperior*alternativetotheSingletondesignpattern,inwhichtheinstanceisa*singletoninthescopeofthefactory).Whichtypeofinstancewillbereturned*dependsonthebeanfactoryconfiguration:theAPIisthesame.SinceSpring*2.0,furtherscopesareavailabledependingontheconcreteapplication*context(e.g.requestandsessionscopesinawebenvironment).*ThepointofthisapproachisthattheBeanFactoryisacentralregistry*ofapplicationcomponents,andcentralizesconfigurationofapplication*components(nomoredoindividualobjectsneedtoreadpropertiesfiles,*forexample).Seechapters4and11ofExpertOne-on-OneJ2EEDesignand*Developmentforadiscussionofthebenefitsofthisapproach.*NotethatitisgenerallybettertorelyonDependencyInjection*(pushconfiguration)toconfigureapplicationobjectsthroughsetters*orconstructors,ratherthanuseanyformofpullconfigurationlikea*BeanFactorylookup.SpringsDependencyInjectionfunctionalityis*implementedusingthisBeanFactoryinterfaceanditssubinterfaces.*NormallyaBeanFactorywillloadbeandefinitionsstoredinaconfiguration*source(suchasanXMLdocument),andusetheorg.springframework.beans*packagetoconfigurethebeans.However,animplementationcouldsimplyreturn*JavaobjectsitcreatesasnecessarydirectlyinJavacode.Thereareno*constraintsonhowthedefinitionscouldbestored:LDAP,RDBMS,XML,*propertiesfile,etc.Implementationsareencouragedtosupportreferences*amongstbeans(DependencyInjection).*IncontrasttothemethodsinlinkListableBeanFactory,allofthe*operationsinthisinterfacewillalsocheckparentfactoriesifthisisa*linkHierarchicalBeanFactory.Ifabeanisnotfoundinthisfactoryinstance,*theimmediateparentfactorywillbeasked.Beansinthisfactoryinstance*aresupposedtooverridebeansofthesamenameinanyparentfactory.*Beanfactoryimplementationsshouldsupportthestandardbeanlifecycleinterfaces*asfaraspossible.Thefullsetofinitializationmethodsandtheirstandardorderis:*1.BeanNameAwaressetBeanName*2.BeanClassLoaderAwaressetBeanClassLoader*3.BeanFactoryAwaressetBeanFactory*4.ResourceLoaderAwaressetResourceLoader*(onlyapplicablewhenrunninginanapplicationcontext)*5.ApplicationEventPublisherAwaressetApplicationEventPublisher*(onlyapplicablewhenrunninginanapplicationcontext)*6.MessageSourceAwaressetMessageSource*(onlyapplicablewhenrunninginanapplicationcontext)*7.ApplicationContextAwaressetApplicationContext*(onlyapplicablewhenrunninginanapplicationcontext)*8.ServletContextAwaressetServletContext*(onlyapplicablewhenrunninginawebapplicationcontext)*9.postProcessBeforeInitializationmethodsofBeanPostProcessors*10.InitializingBeansafterPropertiesSet*11.acustominit-methoddefinition*12.postProcessAfterInitializationmethodsofBeanPostProcessors*Onshutdownofabeanfactory,thefollowinglifecyclemethodsapply:*1.DisposableBeansdestroy*2.acustomdestroy-methoddefinition*authorRodJohnson*authorJuergenHoeller*since13April2001*seeBeanNameAware#setBeanName*seeBeanClassLoaderAware#setBeanClassLoader*seeBeanFactoryAware#setBeanFactory*seeorg.springframework.context.ResourceLoaderAware#setResourceLoader*seeorg.springframework.context.ApplicationEventPublisherAware#setApplicationEventPublisher*seeorg.springframework.context.MessageSourceAware#setMessageSource*seeorg.springframework.context.ApplicationContextAware#setApplicationContext*seeorg.springframework.web.context.ServletContextAware#setServletContext*seeorg.springframework.beans.factory.config.BeanPostProcessor#postProcessBeforeInitialization*seeInitializingBean#afterPropertiesSet*seeorg.springframework.beans.factory.support.RootBeanDefinition#getInitMethodName*seeorg.springframework.beans.factory.config.BeanPostProcessor#postProcessAfterInitialization*seeDisposableBean#destroy*seeorg.springframework.beans.factory.support.RootBeanDefinition#getDestroyMethodName*/publicinterfaceBeanFactory/*UsedtodereferencealinkFactoryBeaninstanceanddistinguishitfrom*beanscreatedbytheFactoryBean.Forexample,ifthebeannamed*myJndiObjectisaFactoryBean,getting&myJndiObject*willreturnthefactory,nottheinstancereturnedbythefactory.*/StringFACTORY_BEAN_PREFIX=&;/*Returnaninstance,whichmaybesharedorindependent,ofthespecifiedbean.*ThismethodallowsaSpringBeanFactorytobeusedasareplacementforthe*SingletonorPrototypedesignpattern.Callersmayretainreferencesto*returnedobjectsinthecaseofSingletonbeans.*Translatesaliasesbacktothecorrespondingcanonicalbeanname.*Willasktheparentfactoryifthebeancannotbefoundinthisfactoryinstance.*paramnamethenameofthebeantoretrieve*returnaninstanceofthebean*throwsNoSuchBeanDefinitionExceptionifthereisnobeandefinition*withthespecifiedname*throwsBeansExceptionifthebeancouldnotbeobtained*/ObjectgetBean(Stringname)throwsBeansException;/*Returnaninstance,whichmaybesharedorindependent,ofthespecifiedbean.*Behavesthesameaslink#getBean(String),butprovidesameasureoftype*safetybythrowingaBeanNotOfRequiredTypeExceptionifthebeanisnotofthe*requiredtype.ThismeansthatClassCastExceptioncantbethrownoncasting*theresultcorrectly,ascanhappenwithlink#getBean(String).*Translatesaliasesbacktothecorrespondingcanonicalbeanname.*Willasktheparentfactoryifthebeancannotbefoundinthisfactoryinstance.*paramnamethenameofthebeantoretrieve*paramrequiredTypetypethebeanmustmatch.Canbeaninterfaceorsuperclass*oftheactualclass,ornullforanymatch.Forexample,ifthevalue*isObject.class,thismethodwillsucceedwhatevertheclassofthe*returnedinstance.*returnaninstanceofthebean*throwsNoSuchBeanDefinitionExceptioniftheresnosuchbeandefinition*throwsBeanNotOfRequiredTypeExceptionifthebeanisnotoftherequiredtype*throwsBeansExceptionifthebeancouldnotbecreated*/TgetBean(Stringname,ClassrequiredType)throwsBeansException;/*Returnthebeaninstancethatuniquelymatchesthegivenobjecttype,ifany.*paramrequiredTypetypethebeanmustmatch;canbeaninterfaceorsuperclass.*literalnullisdisallowed.*ThismethodgoesintolinkListableBeanFactoryby-typelookupterritory*butmayalsobetranslatedintoaconventionalby-namelookupbasedonthename*ofthegiventype.Formoreextensiveretrievaloperationsacrosssetsofbeans,*uselinkListableBeanFactoryand/orlinkBeanFactoryUtils.*returnaninstanceofthesinglebeanmatchingtherequiredtype*throwsNoSuchBeanDefinitionExceptionifthereisnotexactlyonematchingbeanfound*since3.0*seeListableBeanFactory*/TgetBean(ClassrequiredType)throwsBeansException;/*Returnaninstance,whichmaybesharedorindependent,ofthespecifiedbean.*Allowsforspecifyingexplicitconstructorarguments/factorymethodarguments,*overridingthespecifieddefaultarguments(ifany)inthebeandefinition.*paramnamethenameofthebeantoretrieve*paramargsargumentstouseifcreatingaprototypeusingexplicitargumentstoa*staticfactorymethod.Itisinvalidtouseanon-nullargsvalueinanyothercase.*returnaninstanceofthebean*throwsNoSuchBeanDefinitionExceptioniftheresnosuchbeandefinition*throwsBeanDefinitionStoreExceptionifargumentshavebeengivenbut*theaffectedbeanisntaprototype*throwsBeansExceptionifthebeancouldnotbecreated*since2.5*/ObjectgetBean(Stringname,Object.args)throwsBeansException;/*Doesthisbeanfactorycontainabeanwiththegivenname?Morespecifically,*islink#getBeanabletoobtainabeaninstanceforthegivenname?*Translatesaliasesbacktothecorrespondingcanonicalbeanname.*Willasktheparentfactoryifthebeancannotbefoundinthisfactoryinstance.*paramnamethenameofthebeantoquery*returnwhetherabeanwiththegivennameisdefined*/booleancontainsBean(Stringname);/*Isthisbeanasharedsingleton?Thatis,willlink#getBeanalways*returnthesameinstance?*Note:Thismethodreturningfalsedoesnotclearlyindicate*independentinstances.Itindicatesnon-singletoninstances,whichmaycorrespond*toascopedbeanaswell.Usethelink#isPrototypeoperationtoexplicitly*checkforindependentinstances.*Translatesaliasesbacktothecorrespondingcanonicalbeanname.*Willasktheparentfactoryifthebeancannotbefoundinthisfactoryinstance.*paramnamethenameofthebeantoquery*returnwhetherthisbeancorrespondstoasingletoninstance*throwsNoSuchBeanDefinitionExceptionifthereisnobeanwiththegivenname*see#getBean*see#isPrototype*/booleanisSingleton(Stringname)throwsNoSuchBeanDefinitionException;/*Isthisbeanaprototype?Thatis,willlink#getBeanalwaysreturn*independentinstances?*Note:Thismethodreturningfalsedoesnotclearlyindicate*asingletonobject.Itindicatesnon-independentinstances,whichmaycorrespond*toascopedbeanaswell.Usethelink#isSingletonoperationtoexplicitly*checkforasharedsingletoninstance.*Translatesaliasesbacktothecorrespondingcanonicalbeanname.*Willasktheparentfactoryifthebeancannotbefoundinthisfactoryinstance.*paramnamethenameofthebeantoquery*returnwhetherthisbeanwillalwaysdeliverindependentinstances*throwsNoSuchBeanDefinitionExceptionifthereisnobeanwiththegivenname*since2.0.3*see#getBean*see#isSingleton*/booleanisPrototype(Stringname)throwsNoSuchBeanDefinitionException;/*Checkwhetherthebeanwiththegivennamematchesthespecifiedtype.*Morespecifically,checkwhetheralink#getBeancallforthegivenname*wouldreturnanobjectthatisassignabletothespecifiedtargettype.*Translatesaliasesbacktothecorrespondingcanonicalbeanname.*Willasktheparentfactoryifthebeancannotbefoundinthisfactoryinstance.*paramnamethenameofthebeantoquery*paramtargetTypethetypetomatchagainst*returntrueifthebeantypematches,*falseifitdoesntmatchorcannotbedeterminedyet*throwsNoSuchBeanDefinitionExceptionifthereisnobeanwiththegivenname*since2.0.1*see#getBean*see#getType*/booleanisTypeMatch(Stringname,ClasstargetType)throwsNoSuchBeanDefinitionException;/*Determinethetypeofthebeanwiththegivenname.Morespecifically,*determinethetypeofobjectthatlink#getBeanwouldreturnforthegivenname.*ForalinkFactoryBean,returnthetypeofobjectthattheFactoryBeancreates,*asexposedbylinkFactoryBean#getObjectType().*Translatesaliasesbacktothecorrespondingcanonicalbeanname.*Willasktheparentfactoryifthebeancannotbefoundinthisfactoryinstance.*paramnamethenameofthebeantoquery*returnthetypeofthebean,ornullifnotdeterminable*throwsNoSuchBeanDefinitionExceptionifthereisnobeanwiththegivenname*since1.1.2*see#getBean*see#isTypeMatch*/ClassgetType(Stringname)throwsNoSuchBeanDefinitionException;/*Returnthealiasesforthegivenbeanname,ifany.*Allofthosealiasespointtothesamebeanwhenusedinalink#getBeancall.*Ifthegivennameisanalias,thecorrespondingoriginalbeanname*andotheraliases(ifany)willbereturned,withtheoriginalbeanname*beingthefirstelementinthearray.*Willasktheparentfactoryifthebeancannotbefoundinthisfactoryinstance.*paramnamethebeannametocheckforaliases*returnthealiases,oranemptyarrayifnone*see#getBean*/StringgetAliases(Stringname);这个便是spring核心的Bean工厂定义，上面的author说是2001年写的，已经历史久远了，这个类是spring中所有bean工厂，也就是俗称的IOC容器的祖宗，各种IOC容器都只是它的实现或者为了满足特别需求的扩展实现，包括我们平时用的最多的ApplicationContext。从上面的方法就可以看出，这些工厂的实现最大的作用就是根据bean的名称亦或类型等等，来返回一个bean的实例。一个工厂如果想拥有这样的功能，那么它一定需要以下几个因素：1.需要持有各种bean的定义，否则无法正确的完成bean的实例化。2.需要持有bean之间的依赖关系，否则在bean实例化的过程中也会出现问题。例如上例，如果我们只是各自持有Person和Company，却不知道他们的依赖关系，那么在Company初始化以后，调用open方法时，就会报空指针。这是因为Company其实并没有真正的被正确初始化。3.以上两种都要依赖于我们所写的依赖关系的定义，暂且认为是XML文件（其实可以是各种各样的），那么我们需要一个工具来完成XML文件的读取。我目前想到的，只需要满足以上三种条件，便可以创建一个bean工厂，来生产各种bean。当然，spring有更高级的做法，以上只是我们直观的去想如何实现IOC。其实在上述过程中仍旧有一些问题，比如第一步，我们需要持有bean的定义，如何持有？这是一个问题。我们知道spring的XML配置文件中，有一个属性是lazy-init，这就说明，bean在何时实例化我们是可以控制的。这个属性默认是false，但是我们可以将这个属性设置为true，也就是说spring容器初始化以后，配置了延迟加载的各种bean都还未产生，它们只在需要的时候出现。所以我们无法直接的创建一个Map来持有这些bean的实例，在这里要注意，我们要储存的是bean的定义，而非实例。那么接下来，又是一个祖宗级别的接口要出现了，来看BeanDefinition。/*Copyright2002-2009theoriginalauthororauthors.*LicensedundertheApacheLicense,Version2.0(theLicense);*youmaynotusethisfileexceptincompliancewiththeLicense.*YoumayobtainacopyoftheLicenseat*/licenses/LICENSE-2.0*Unlessrequiredbyapplicablelaworagreedtoinwriting,software*distributedundertheLicenseisdistributedonanASISBASIS,*WITHOUTWARRANTIESORCONDITIONSOFANYKIND,eitherexpressorimplied.*SeetheLicenseforthespecificlanguagegoverningpermissionsand*limitationsundertheLicense.*/packageorg.springframework.beans.factory.config;importorg.springframework.beans.BeanMetadataElement;importorg.springframework.beans.MutablePropertyValues;importorg.springframework.core.AttributeAccessor;/*ABeanDefinitiondescribesabeaninstance,whichhaspropertyvalues,*constructorargumentvalues,andfurtherinformationsuppliedby*concreteimplementations.*Thisisjustaminimalinterface:Themainintentionistoallowa*linkBeanFactoryPostProcessorsuchaslinkPropertyPlaceholderConfigurer*tointrospectandmodifypropertyvaluesandotherbeanmetadata.*authorJuergenHoeller*authorRobHarrop*since19.03.2004*seeConfigurableListableBeanFactory#getBeanDefinition*seeorg.springframework.beans.factory.support.RootBeanDefinition*seeorg.springframework.beans.factory.support.ChildBeanDefinition*/publicinterfaceBeanDefinitionextendsAttributeAccessor,BeanMetadataElement/*Scopeidentifierforthestandardsingletonscope:singleton.*Notethatextendedbeanfactoriesmightsupportfurtherscopes.*see#setScope*/StringSCOPE_SINGLETON=ConfigurableBeanFactory.SCOPE_SINGLETON;/*Scopeidentifierforthestandardprototypescope:prototype.*Notethatextendedbeanfactoriesmightsupportfurtherscopes.*see#setScope*/StringSCOPE_PROTOTYPE=ConfigurableBeanFactory.SCOPE_PROTOTYPE;/*RolehintindicatingthataBeanDefinitionisamajorpart*oftheapplication.Typicallycorrespondstoauser-definedbean.*/intROLE_APPLICATION=0;/*RolehintindicatingthataBeanDefinitionisasupporting*partofsomelargerconfiguration,typicallyanouter*linkorg.springframework.beans.factory.parsing.ComponentDefinition.*SUPPORTbeansareconsideredimportantenoughtobeaware*ofwhenlookingmorecloselyataparticular*linkorg.springframework.beans.factory.parsing.ComponentDefinition,*butnotwhenlookingattheoverallconfigurationofanapplication.*/intROLE_SUPPORT=1;/*RolehintindicatingthataBeanDefinitionisprovidingan*entirelybackgroundroleandhasnorelevancetotheend-user.Thishintis*usedwhenregisteringbeansthatarecompletelypartoftheinternalworkings*ofalinkorg.springframework.beans.factory.parsing.ComponentDefinition.*/intROLE_INFRASTRUCTURE=2;/*Returnthenameoftheparentdefinitionofthisbeandefinition,ifany.*/StringgetParentName();/*Setthenameoftheparentdefinitionofthisbeandefinition,ifany.*/voidsetParentName(StringparentName);/*Returnthecurrentbeanclassnameofthisbeandefinition.*Notethatthisdoesnothavetobetheactualclassnameusedatruntime,in*caseofachilddefinitionoverri