Spring IOC源碼分析 ，寫得真好！

group?'org.springframework'
version?'5.1.21.BUILD-SNAPSHOT'

apply?plugin:?'java'

sourceCompatibility?=?1.8

repositories?{
????mavenCentral()
}

dependencies?{
????compile(project(":spring-context"))
????testCompile?group:?'junit',?name:?'junit',?version:?'4.12'
}

public?void?refresh()?throws?BeansException,?IllegalStateException?{
??synchronized?(this.startupShutdownMonitor)?{
???//第一步：刷新前的預處理
???prepareRefresh();

???//?第二步：獲取BeanFactory；加載BeanDefition并注冊到BeanDefitionRegistry
???ConfigurableListableBeanFactory?beanFactory?=?obtainFreshBeanFactory();

???//?第三步：BeanFactory的預準備工作
???prepareBeanFactory(beanFactory);

???try?{
????//?第四步：BeanFactory準備工作完成之后進行的后置處理
????postProcessBeanFactory(beanFactory);

????//?第五步：實例化并調用實現(xiàn)了BeanFactoryPostProcessor接口的Bean
????invokeBeanFactoryPostProcessors(beanFactory);

????//?第六步：注冊BeanPostProcessor，在創(chuàng)建bean的前后等執(zhí)行。
????registerBeanPostProcessors(beanFactory);

????//?第七步：初始化MessageSource組件（做國際化功能；消息綁定，消息解析）
????initMessageSource();

????//?第八步：初始化事件派發(fā)器
????initApplicationEventMulticaster();

????//第九步：提供給子類重寫，容器刷新的適合可以自定義邏輯
????onRefresh();

????//?第十步：注冊應用監(jiān)聽器。就是注冊實現(xiàn)了ApplicationListener接口的監(jiān)聽器bean
????registerListeners();

????//?第十一步：初始化所有剩下的非懶加載的單例bean，
????//填充屬性
????//初始化方法調用
????//調用BeanPostProcessor對bean進行后置處理
????finishBeanFactoryInitialization(beanFactory);

????//?第十二步：完成context的刷新。主要是調用LifecycleProcessor的onRefresh方法，并且發(fā)布ContextRefreshedEvent事件
????finishRefresh();
???}

???catch?(BeansException?ex)?{
????if?(logger.isWarnEnabled())?{
?????logger.warn("Exception?encountered?during?context?initialization?-?"?+
???????"cancelling?refresh?attempt:?"?+?ex);
????}

????//?Destroy?already?created?singletons?to?avoid?dangling?resources.
????destroyBeans();

????//?Reset?'active'?flag.
????cancelRefresh(ex);

????//?Propagate?exception?to?caller.
????throw?ex;
???}

???finally?{
????//?Reset?common?introspection?caches?in?Spring's?core,?since?we
????//?might?not?ever?need?metadata?for?singleton?beans?anymore...
????resetCommonCaches();
???}
??}
?}

protected?int?doLoadBeanDefinitions(InputSource?inputSource,?Resource?resource)
???throws?BeanDefinitionStoreException?{

??try?{
???//讀取xml信息，將xml信息保存到Document中
???Document?doc?=?doLoadDocument(inputSource,?resource);
???//解析doc，封裝到BeanDefinition對象并進行注冊
???int?count?=?registerBeanDefinitions(doc,?resource);
???if?(logger.isDebugEnabled())?{
????logger.debug("Loaded?"?+?count?+?"?bean?definitions?from?"?+?resource);
???}
???return?count;
??}
?//省略部分代碼....

public?int?registerBeanDefinitions(Document?doc,?Resource?resource)?throws?BeanDefinitionStoreException?{
??BeanDefinitionDocumentReader?documentReader?=?createBeanDefinitionDocumentReader();
??//獲取已有的BeanDefinition的數(shù)量
??int?countBefore?=?getRegistry().getBeanDefinitionCount();
??//注冊BeanDefinitions
??documentReader.registerBeanDefinitions(doc,?createReaderContext(resource));
??//返回新注冊的BeanDefinition的數(shù)量
??return?getRegistry().getBeanDefinitionCount()?-?countBefore;
?}

protected?void?doRegisterBeanDefinitions(Element?root)?{
?????//省略部分代碼...
??preProcessXml(root);
??parseBeanDefinitions(root,?this.delegate);
??postProcessXml(root);

??this.delegate?=?parent;
?}

private?void?parseDefaultElement(Element?ele,?BeanDefinitionParserDelegate?delegate)?{
??//import處理
??if?(delegate.nodeNameEquals(ele,?IMPORT_ELEMENT))?{
???importBeanDefinitionResource(ele);
??}
??//alias處理
??else?if?(delegate.nodeNameEquals(ele,?ALIAS_ELEMENT))?{
???processAliasRegistration(ele);
??}
??//解析bean元素
??else?if?(delegate.nodeNameEquals(ele,?BEAN_ELEMENT))?{
???processBeanDefinition(ele,?delegate);
??}
??//嵌套bean處理
??else?if?(delegate.nodeNameEquals(ele,?NESTED_BEANS_ELEMENT))?{
???//?recurse
???doRegisterBeanDefinitions(ele);
??}
?}

protected?void?processBeanDefinition(Element?ele,?BeanDefinitionParserDelegate?delegate)?{
??//解析bean元素為BeanDefinition,但是此時使用BeanDefinitionHolder又包裝了一層
??BeanDefinitionHolder?bdHolder?=?delegate.parseBeanDefinitionElement(ele);
??if?(bdHolder?!=?null)?{
???bdHolder?=?delegate.decorateBeanDefinitionIfRequired(ele,?bdHolder);
???try?{
????//?完成BeanDefinition的注冊
????BeanDefinitionReaderUtils.registerBeanDefinition(bdHolder,?getReaderContext().getRegistry());
???}
???catch?(BeanDefinitionStoreException?ex)?{
????getReaderContext().error("Failed?to?register?bean?definition?with?name?'"?+
??????bdHolder.getBeanName()?+?"'",?ele,?ex);
???}
???//?Send?registration?event.
???getReaderContext().fireComponentRegistered(new?BeanComponentDefinition(bdHolder));
??}
?}

this.beanDefinitionMap.put(beanName,?beanDefinition);

protected?void?finishBeanFactoryInitialization(ConfigurableListableBeanFactory?beanFactory)?{
??//省略部分代碼...
??String[]?weaverAwareNames?=?beanFactory.getBeanNamesForType(LoadTimeWeaverAware.class,?false,?false);
??for?(String?weaverAwareName?:?weaverAwareNames)?{
???getBean(weaverAwareName);
??}

??//?Stop?using?the?temporary?ClassLoader?for?type?matching.
??beanFactory.setTempClassLoader(null);

??//?Allow?for?caching?all?bean?definition?metadata,?not?expecting?further?changes.
??beanFactory.freezeConfiguration();

??//?實例化所有非懶加載的bean
??beanFactory.preInstantiateSingletons();
?}

public?void?preInstantiateSingletons()?throws?BeansException?{
??if?(logger.isTraceEnabled())?{
???logger.trace("Pre-instantiating?singletons?in?"?+?this);
??}

??//?Iterate?over?a?copy?to?allow?for?init?methods?which?in?turn?register?new?bean?definitions.
??//?While?this?may?not?be?part?of?the?regular?factory?bootstrap,?it?does?otherwise?work?fine.
??List?beanNames?=?new?ArrayList<>(this.beanDefinitionNames);

??//?遍歷所有的beanName
??for?(String?beanName?:?beanNames)?{
???RootBeanDefinition?bd?=?getMergedLocalBeanDefinition(beanName);
???if?(!bd.isAbstract()?&&?bd.isSingleton()?&&?!bd.isLazyInit())?{
????//如果是工廠bean，即實現(xiàn)了FactoryBean接口
????if?(isFactoryBean(beanName))?{
?????Object?bean?=?getBean(FACTORY_BEAN_PREFIX?+?beanName);
?????if?(bean?instanceof?FactoryBean)?{
??????FactoryBean?factory?=?(FactoryBean)?bean;
??????boolean?isEagerInit;
??????if?(System.getSecurityManager()?!=?null?&&?factory?instanceof?SmartFactoryBean)?{
???????isEagerInit?=?AccessController.doPrivileged(
?????????(PrivilegedAction)?((SmartFactoryBean)?factory)::isEagerInit,
?????????getAccessControlContext());
??????}
??????else?{
???????isEagerInit?=?(factory?instanceof?SmartFactoryBean?&&
?????????((SmartFactoryBean)?factory).isEagerInit());
??????}
??????if?(isEagerInit)?{
???????getBean(beanName);
??????}
?????}
????}
????else?{
?????//實例化當前bean
?????getBean(beanName);
????}
???}
??}
????//省略...
?}

protected??T?doGetBean(
???String?name,?@Nullable?Class?requiredType,?@Nullable?Object[]?args,?boolean?typeCheckOnly)
???throws?BeansException?{

??String?beanName?=?transformedBeanName(name);
??Object?bean;

??//?從緩存中拿
??Object?sharedInstance?=?getSingleton(beanName);
??if?(sharedInstance?!=?null?&&?args?==?null)?{
???if?(logger.isTraceEnabled())?{
????if?(isSingletonCurrentlyInCreation(beanName))?{
?????logger.trace("Returning?eagerly?cached?instance?of?singleton?bean?'"?+?beanName?+
???????"'?that?is?not?fully?initialized?yet?-?a?consequence?of?a?circular?reference");
????}
????else?{
?????logger.trace("Returning?cached?instance?of?singleton?bean?'"?+?beanName?+?"'");
????}
???}
???bean?=?getObjectForBeanInstance(sharedInstance,?name,?beanName,?null);
??}

??else?{
???//如果已經(jīng)有創(chuàng)建過程中的同beanName的bean，拋異常
???if?(isPrototypeCurrentlyInCreation(beanName))?{
????throw?new?BeanCurrentlyInCreationException(beanName);
???}

???//?從parentBeanFactory里找對應的bean
???BeanFactory?parentBeanFactory?=?getParentBeanFactory();
???if?(parentBeanFactory?!=?null?&&?!containsBeanDefinition(beanName))?{
????//?Not?found?->?check?parent.
????String?nameToLookup?=?originalBeanName(name);
????if?(parentBeanFactory?instanceof?AbstractBeanFactory)?{
?????return?((AbstractBeanFactory)?parentBeanFactory).doGetBean(
???????nameToLookup,?requiredType,?args,?typeCheckOnly);
????}
????else?if?(args?!=?null)?{
?????//?Delegation?to?parent?with?explicit?args.
?????return?(T)?parentBeanFactory.getBean(nameToLookup,?args);
????}
????else?if?(requiredType?!=?null)?{
?????//?No?args?->?delegate?to?standard?getBean?method.
?????return?parentBeanFactory.getBean(nameToLookup,?requiredType);
????}
????else?{
?????return?(T)?parentBeanFactory.getBean(nameToLookup);
????}
???}

???if?(!typeCheckOnly)?{
????//打一個已創(chuàng)建的標記
????markBeanAsCreated(beanName);
???}

???try?{
????RootBeanDefinition?mbd?=?getMergedLocalBeanDefinition(beanName);
????checkMergedBeanDefinition(mbd,?beanName,?args);

????//?保證當前bean所依賴的bean的初始化
????String[]?dependsOn?=?mbd.getDependsOn();
????if?(dependsOn?!=?null)?{
?????for?(String?dep?:?dependsOn)?{
??????if?(isDependent(beanName,?dep))?{
???????throw?new?BeanCreationException(mbd.getResourceDescription(),?beanName,
?????????"Circular?depends-on?relationship?between?'"?+?beanName?+?"'?and?'"?+?dep?+?"'");
??????}
??????registerDependentBean(dep,?beanName);
??????try?{
???????getBean(dep);
??????}
??????catch?(NoSuchBeanDefinitionException?ex)?{
???????throw?new?BeanCreationException(mbd.getResourceDescription(),?beanName,
?????????"'"?+?beanName?+?"'?depends?on?missing?bean?'"?+?dep?+?"'",?ex);
??????}
?????}
????}

????//創(chuàng)建bean
????//?單例bean
????if?(mbd.isSingleton())?{
?????sharedInstance?=?getSingleton(beanName,?()?->?{
??????try?{
???????//具體的創(chuàng)建bean邏輯
???????return?createBean(beanName,?mbd,?args);
??????}
??????catch?(BeansException?ex)?{
???????//?Explicitly?remove?instance?from?singleton?cache:?It?might?have?been?put?there
???????//?eagerly?by?the?creation?process,?to?allow?for?circular?reference?resolution.
???????//?Also?remove?any?beans?that?received?a?temporary?reference?to?the?bean.
???????destroySingleton(beanName);
???????throw?ex;
??????}
?????});
?????bean?=?getObjectForBeanInstance(sharedInstance,?name,?beanName,?mbd);
????}
????//多例bean
????else?if?(mbd.isPrototype())?{
?????//?It's?a?prototype?->?create?a?new?instance.
?????Object?prototypeInstance?=?null;
?????try?{
??????beforePrototypeCreation(beanName);
??????prototypeInstance?=?createBean(beanName,?mbd,?args);
?????}
?????finally?{
??????afterPrototypeCreation(beanName);
?????}
?????bean?=?getObjectForBeanInstance(prototypeInstance,?name,?beanName,?mbd);
????}

????else?{
?????String?scopeName?=?mbd.getScope();
?????if?(!StringUtils.hasLength(scopeName))?{
??????throw?new?IllegalStateException("No?scope?name?defined?for?bean?′"?+?beanName?+?"'");
?????}
?????Scope?scope?=?this.scopes.get(scopeName);
?????if?(scope?==?null)?{
??????throw?new?IllegalStateException("No?Scope?registered?for?scope?name?'"?+?scopeName?+?"'");
?????}
?????try?{
??????Object?scopedInstance?=?scope.get(beanName,?()?->?{
???????beforePrototypeCreation(beanName);
???????try?{
????????return?createBean(beanName,?mbd,?args);
???????}
???????finally?{
????????afterPrototypeCreation(beanName);
???????}
??????});
??????bean?=?getObjectForBeanInstance(scopedInstance,?name,?beanName,?mbd);
?????}
?????catch?(IllegalStateException?ex)?{
??????throw?new?BeanCreationException(beanName,
????????"Scope?'"?+?scopeName?+?"'?is?not?active?for?the?current?thread;?consider?"?+
????????"defining?a?scoped?proxy?for?this?bean?if?you?intend?to?refer?to?it?from?a?singleton",
????????ex);
?????}
????}
???}
???catch?(BeansException?ex)?{
????cleanupAfterBeanCreationFailure(beanName);
????throw?ex;
???}
??}

??//?檢查所需類型是否與實際bean實例的類型匹配。
??if?(requiredType?!=?null?&&?!requiredType.isInstance(bean))?{
???try?{
????T?convertedBean?=?getTypeConverter().convertIfNecessary(bean,?requiredType);
????if?(convertedBean?==?null)?{
?????throw?new?BeanNotOfRequiredTypeException(name,?requiredType,?bean.getClass());
????}
????return?convertedBean;
???}
???catch?(TypeMismatchException?ex)?{
????if?(logger.isTraceEnabled())?{
?????logger.trace("Failed?to?convert?bean?'"?+?name?+?"'?to?required?type?'"?+
???????ClassUtils.getQualifiedName(requiredType)?+?"'",?ex);
????}
????throw?new?BeanNotOfRequiredTypeException(name,?requiredType,?bean.getClass());
???}
??}
??return?(T)?bean;
?}

protected?Object?doCreateBean(String?beanName,?RootBeanDefinition?mbd,?@Nullable?Object[]?args)
???throws?BeanCreationException?{

??//?Instantiate?the?bean.
??BeanWrapper?instanceWrapper?=?null;
??if?(mbd.isSingleton())?{
???instanceWrapper?=?this.factoryBeanInstanceCache.remove(beanName);
??}
??if?(instanceWrapper?==?null)?{
???//創(chuàng)建bean實例，但是尚未設置屬性
???instanceWrapper?=?createBeanInstance(beanName,?mbd,?args);
??}
??Object?bean?=?instanceWrapper.getWrappedInstance();
??Class?beanType?=?instanceWrapper.getWrappedClass();
??if?(beanType?!=?NullBean.class)?{
???mbd.resolvedTargetType?=?beanType;
??}

??//允許后處理器修改合并的bean定義
??synchronized?(mbd.postProcessingLock)?{
???if?(!mbd.postProcessed)?{
????try?{
?????applyMergedBeanDefinitionPostProcessors(mbd,?beanType,?beanName);
????}
????catch?(Throwable?ex)?{
?????throw?new?BeanCreationException(mbd.getResourceDescription(),?beanName,
???????"Post-processing?of?merged?bean?definition?failed",?ex);
????}
????mbd.postProcessed?=?true;
???}
??}

??//急切地緩存單例，以便能夠解析循環(huán)引用
??//即使由BeanFactoryAware等生命周期接口觸發(fā)。
??boolean?earlySingletonExposure?=?(mbd.isSingleton()?&&?this.allowCircularReferences?&&
????isSingletonCurrentlyInCreation(beanName));
??if?(earlySingletonExposure)?{
???if?(logger.isTraceEnabled())?{
????logger.trace("Eagerly?caching?bean?'"?+?beanName?+
??????"'?to?allow?for?resolving?potential?circular?references");
???}
???addSingletonFactory(beanName,?()?->?getEarlyBeanReference(beanName,?mbd,?bean));
??}

??//?Initialize?the?bean?instance.
??Object?exposedObject?=?bean;
??try?{
???//設置屬性
???populateBean(beanName,?mbd,?instanceWrapper);
???//應用初始化方法，調用BeanPostProcessor后置處理器
???exposedObject?=?initializeBean(beanName,?exposedObject,?mbd);
??}
??catch?(Throwable?ex)?{
???if?(ex?instanceof?BeanCreationException?&&?beanName.equals(((BeanCreationException)?ex).getBeanName()))?{
????throw?(BeanCreationException)?ex;
???}
???else?{
????throw?new?BeanCreationException(
??????mbd.getResourceDescription(),?beanName,?"Initialization?of?bean?failed",?ex);
???}
??}

??if?(earlySingletonExposure)?{
???Object?earlySingletonReference?=?getSingleton(beanName,?false);
???if?(earlySingletonReference?!=?null)?{
????if?(exposedObject?==?bean)?{
?????exposedObject?=?earlySingletonReference;
????}
????else?if?(!this.allowRawInjectionDespiteWrapping?&&?hasDependentBean(beanName))?{
?????String[]?dependentBeans?=?getDependentBeans(beanName);
?????Set?actualDependentBeans?=?new?LinkedHashSet<>(dependentBeans.length);
?????for?(String?dependentBean?:?dependentBeans)?{
??????if?(!removeSingletonIfCreatedForTypeCheckOnly(dependentBean))?{
???????actualDependentBeans.add(dependentBean);
??????}
?????}
?????if?(!actualDependentBeans.isEmpty())?{
??????throw?new?BeanCurrentlyInCreationException(beanName,
????????"Bean?with?name?'"?+?beanName?+?"'?has?been?injected?into?other?beans?["?+
????????StringUtils.collectionToCommaDelimitedString(actualDependentBeans)?+
????????"]?in?its?raw?version?as?part?of?a?circular?reference,?but?has?eventually?been?"?+
????????"wrapped.?This?means?that?said?other?beans?do?not?use?the?final?version?of?the?"?+
????????"bean.?This?is?often?the?result?of?over-eager?type?matching?-?consider?using?"?+
????????"'getBeanNamesForType'?with?the?'allowEagerInit'?flag?turned?off,?for?example.");
?????}
????}
???}
??}

??//?Register?bean?as?disposable.
??try?{
???registerDisposableBeanIfNecessary(beanName,?bean,?mbd);
??}
??catch?(BeanDefinitionValidationException?ex)?{
???throw?new?BeanCreationException(
?????mbd.getResourceDescription(),?beanName,?"Invalid?destruction?signature",?ex);
??}

??return?exposedObject;
?}