spring源码解析二（ getBean()）
前面分析了解析bean定义信息，接下来就是通过bean定义生成我们需要的bean对象
1、refresh()
其中org.springframework.context.support.AbstractApplicationContext#refresh方法中有十二步，前面分析了第五步invokeBeanFactoryPostProcessors，这里来看下第十一步finishBeanFactoryInitialization(beanFactory)
protected void finishBeanFactoryInitialization(ConfigurableListableBeanFactory beanFactory) { // Initialize conversion service for this context. //为Bean工厂设置类型转化器 //可参考 https://www.cnblogs.com/abcwt112/p/7447435.html if (beanFactory.containsBean(CONVERSION_SERVICE_BEAN_NAME) && beanFactory.isTypeMatch(CONVERSION_SERVICE_BEAN_NAME, ConversionService.class)) { beanFactory.setConversionService( beanFactory.getBean(CONVERSION_SERVICE_BEAN_NAME, ConversionService.class)); } // Register a default embedded value resolver if no bean post-processor // (such as a PropertyPlaceholderConfigurer bean) registered any before: // at this point, primarily for resolution in annotation attribute values. // EmbeddedValueResolver可以用来读取配置文件内容 // 可以通过EmbeddedValueResolverAware来配合使用 if (!beanFactory.hasEmbeddedValueResolver()) { beanFactory.addEmbeddedValueResolver(new StringValueResolver() { @Override public String resolveStringValue(String strVal) { return getEnvironment().resolvePlaceholders(strVal); } }); } // Initialize LoadTimeWeaverAware beans early to allow for registering their transformers early. 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. //冻结所有的Bean定义 ， 至此注册的Bean定义将不被修改或任何进一步的处理 beanFactory.freezeConfiguration(); // Instantiate all remaining (non-lazy-init) singletons. //实例化所有的非懒加载的单例bean beanFactory.preInstantiateSingletons(); }
2、beanFactory.preInstantiateSingletons();
public void preInstantiateSingletons() throws BeansException { if (logger.isDebugEnabled()) { logger.debug("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. //获取我们容器中所有Bean定义的名称 List<String> beanNames = new ArrayList<String>(this.beanDefinitionNames); // Trigger initialization of all non-lazy singleton beans... //循环所有的bean名称 for (String beanName : beanNames) { //合并我们的bean定义 RootBeanDefinition bd = getMergedLocalBeanDefinition(beanName); //判断不是抽象的并且是单例且非懒加载 if (!bd.isAbstract() && bd.isSingleton() && !bd.isLazyInit()) { //是不是实现了factoryBean if (isFactoryBean(beanName)) { //bean名称加上&符号 final FactoryBean<?> factory = (FactoryBean<?>) getBean(FACTORY_BEAN_PREFIX + beanName); boolean isEagerInit; if (System.getSecurityManager() != null && factory instanceof SmartFactoryBean) { isEagerInit = AccessController.doPrivileged(new PrivilegedAction<Boolean>() { @Override public Boolean run() { return ((SmartFactoryBean<?>) factory).isEagerInit(); } }, getAccessControlContext()); } else { isEagerInit = (factory instanceof SmartFactoryBean && ((SmartFactoryBean<?>) factory).isEagerInit()); } if (isEagerInit) { getBean(beanName); } } else { //不是factoryBean的直接实例化本身类 getBean(beanName); } } } // Trigger post-initialization callback for all applicable beans... //获取所有的bean的名称 至此所有的单实例的bean已经加入到单实例Bean的缓存池中 for (String beanName : beanNames) { //获取单实例bean Object singletonInstance = getSingleton(beanName); //判断bean是否实现了SmartInitializingSigleton接口 //触发方法afterSingletonsInstantiated() if (singletonInstance instanceof SmartInitializingSingleton) { final SmartInitializingSingleton smartSingleton = (SmartInitializingSingleton) singletonInstance; if (System.getSecurityManager() != null) { AccessController.doPrivileged(new PrivilegedAction<Object>() { @Override public Object run() { smartSingleton.afterSingletonsInstantiated(); return null; } }, getAccessControlContext()); } else { smartSingleton.afterSingletonsInstantiated(); } } } }
3、getBean(beanName)
public Object getBean(String name) throws BeansException { return doGetBean(name, null, null, false); } protected <T> T doGetBean( final String name, final Class<T> requiredType, final Object[] args, boolean typeCheckOnly) throws BeansException { //在这里传入进来的name可能是别名、也有可能是工厂beanName,所以在这里需要转换 final String beanName = transformedBeanName(name); Object bean; // Eagerly check singleton cache for manually registered singletons. //先去缓存中获取对象，第一次获取肯定是空，创建完成后塞入缓存，后续获取就直接获取到了
//循环依赖时，比如说ab依赖，实例化a之后需要注入b，这时候需要去实例化b，然后向b中注入a，需要获取a的bean,这时候会走到这，
//得到a的一个早期暴露的对象beanFactory,并调用了getObject方法，然后将三级缓存提升为二级缓存，将这个对象注入b,完成b的初始化
Object sharedInstance = getSingleton(beanName); if (sharedInstance != null && args == null) { if (logger.isDebugEnabled()) { //如果是循环依赖的,获取到的实例是实例化完成，但是没有初始化的早期对象 if (isSingletonCurrentlyInCreation(beanName)) { logger.debug("Returning eagerly cached instance of singleton bean '" + beanName + "' that is not fully initialized yet - a consequence of a circular reference"); } else { logger.debug("Returning cached instance of singleton bean '" + beanName + "'"); } } //如果是普通的bean，直接返回， //如果是实现factoryBean的则返回getObject对象 //如果获取factoryBean对象，此时name是以&开头的，内部会直接放回这个factorybean实例 bean = getObjectForBeanInstance(sharedInstance, name, beanName, null); } else { // Fail if we're already creating this bean instance: // We're assumably within a circular reference. //Spring只能解决单例对象的setter注入的循环依赖,不能解决构造器注入，也不能解决多实例的循环依赖 if (isPrototypeCurrentlyInCreation(beanName)) { throw new BeanCurrentlyInCreationException(beanName); } // Check if bean definition exists in this factory. //是否有父类工厂 BeanFactory parentBeanFactory = getParentBeanFactory(); if (parentBeanFactory != null && !containsBeanDefinition(beanName)) { // Not found -> check parent. String nameToLookup = originalBeanName(name); if (args != null) { // Delegation to parent with explicit args. return (T) parentBeanFactory.getBean(nameToLookup, args); } else { // No args -> delegate to standard getBean method. return parentBeanFactory.getBean(nameToLookup, requiredType); } } if (!typeCheckOnly) { //存在alreadyCreated集合中，标记改bean正在穿件中 markBeanAsCreated(beanName); } try { //获取当前bean的定义信息 final RootBeanDefinition mbd = getMergedLocalBeanDefinition(beanName); //检查当前创建的bean定义是不是抽象的bean定义 checkMergedBeanDefinition(mbd, beanName, args); // Guarantee initialization of beans that the current bean depends on. //处理dependsOn的依赖,如果A dependon B，这时候会先去创建B //非循环依赖，只是为了控制bean创建的先后顺序 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 { //先去创建依赖的对象 getBean(dep); } catch (NoSuchBeanDefinitionException ex) { throw new BeanCreationException(mbd.getResourceDescription(), beanName, "'" + beanName + "' depends on missing bean '" + dep + "'", ex); } } } // Create bean instance. //单例的创建 if (mbd.isSingleton()) { //获取单例 //创建ObjectFactory对象，用于回调 sharedInstance = getSingleton(beanName, new ObjectFactory<Object>() { @Override public Object getObject() throws BeansException { try { //创建bean的逻辑 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); } //原型也就是多例的创建 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); } //非原型，非单例，比如request,session什么的 else { String scopeName = mbd.getScope(); final 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, new ObjectFactory<Object>() { @Override public Object getObject() throws BeansException { 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; } } // Check if required type matches the type of the actual bean instance. if (requiredType != null && bean != null && !requiredType.isInstance(bean)) { try { return getTypeConverter().convertIfNecessary(bean, requiredType); } catch (TypeMismatchException ex) { if (logger.isDebugEnabled()) { logger.debug("Failed to convert bean '" + name + "' to required type '" + ClassUtils.getQualifiedName(requiredType) + "'", ex); } throw new BeanNotOfRequiredTypeException(name, requiredType, bean.getClass()); } } return (T) bean; }
4、getSingleton(String beanName, ObjectFactory<?> singletonFactory)
public Object getSingleton(String beanName, ObjectFactory<?> singletonFactory) { Assert.notNull(beanName, "'beanName' must not be null"); //加锁 synchronized (this.singletonObjects) { //先尝试从单例缓存池中获取 Object singletonObject = this.singletonObjects.get(beanName); if (singletonObject == null) { //如果该单例正在销毁中，则报错 if (this.singletonsCurrentlyInDestruction) { throw new BeanCreationNotAllowedException(beanName, "Singleton bean creation not allowed while singletons of this factory are in destruction " + "(Do not request a bean from a BeanFactory in a destroy method implementation!)"); } if (logger.isDebugEnabled()) { logger.debug("Creating shared instance of singleton bean '" + beanName + "'"); } //标记当前的bean马上就要被创建了 //singletonsCurrentlyInCreation 在这里会把beanName加入进来 //用于判断循环依赖，比如ab循环依赖，先创建a,这时候集合中会有a,这时候a初始化的时候需要注入b,这时候会去创建b，创建b这时候需要注入a,发现a正在集合中，可以判断循环依赖，如果是循环依赖就会去早期暴露的对象中去获取实例化但是未初始化的对象 beforeSingletonCreation(beanName); boolean newSingleton = false; boolean recordSuppressedExceptions = (this.suppressedExceptions == null); if (recordSuppressedExceptions) { this.suppressedExceptions = new LinkedHashSet<Exception>(); } try { //回调传进来的singletonFactory对象，调用createBean() singletonObject = singletonFactory.getObject(); newSingleton = true; } catch (IllegalStateException ex) { // Has the singleton object implicitly appeared in the meantime -> // if yes, proceed with it since the exception indicates that state. singletonObject = this.singletonObjects.get(beanName); if (singletonObject == null) { throw ex; } } catch (BeanCreationException ex) { if (recordSuppressedExceptions) { for (Exception suppressedException : this.suppressedExceptions) { ex.addRelatedCause(suppressedException); } } throw ex; } finally { if (recordSuppressedExceptions) { this.suppressedExceptions = null; } //创建完成删除singletonsCurrentlyInCreation 中保存的该beanName，标记该对象已经创建完成 afterSingletonCreation(beanName); } if (newSingleton) { //加入单例缓存池 //移除三级缓存和二级缓存 addSingleton(beanName, singletonObject); } } return (singletonObject != NULL_OBJECT ? singletonObject : null); } }
5、createBean(String beanName, RootBeanDefinition mbd, Object[] args)
protected Object createBean(String beanName, RootBeanDefinition mbd, Object[] args) throws BeanCreationException { if (logger.isDebugEnabled()) { logger.debug("Creating instance of bean '" + beanName + "'"); } RootBeanDefinition mbdToUse = mbd; // Make sure bean class is actually resolved at this point, and // clone the bean definition in case of a dynamically resolved Class // which cannot be stored in the shared merged bean definition. Class<?> resolvedClass = resolveBeanClass(mbd, beanName); if (resolvedClass != null && !mbd.hasBeanClass() && mbd.getBeanClassName() != null) { mbdToUse = new RootBeanDefinition(mbd); mbdToUse.setBeanClass(resolvedClass); } // Prepare method overrides. try { mbdToUse.prepareMethodOverrides(); } catch (BeanDefinitionValidationException ex) { throw new BeanDefinitionStoreException(mbdToUse.getResourceDescription(), beanName, "Validation of method overrides failed", ex); } try { // Give BeanPostProcessors a chance to return a proxy instead of the target bean instance. //调用InstantiationAwareBeanPostProcessor在实例化之前处理 //给bean的后置处理器一个机会来生成一个代理对象返回 //如果bean不为空则直接返回,且内部直接调用了postProcessAfterInstantiation()方法 Object bean = resolveBeforeInstantiation(beanName, mbdToUse); if (bean != null) { return bean; } } catch (Throwable ex) { throw new BeanCreationException(mbdToUse.getResourceDescription(), beanName, "BeanPostProcessor before instantiation of bean failed", ex); } //真正创建bean的逻辑 Object beanInstance = doCreateBean(beanName, mbdToUse, args); if (logger.isDebugEnabled()) { logger.debug("Finished creating instance of bean '" + beanName + "'"); } return beanInstance; }
6、doCreateBean(beanName, mbdToUse, args)
protected Object doCreateBean(final String beanName, final RootBeanDefinition mbd, final Object[] args) throws BeanCreationException { // Instantiate the bean. BeanWrapper instanceWrapper = null; if (mbd.isSingleton()) { instanceWrapper = this.factoryBeanInstanceCache.remove(beanName); } if (instanceWrapper == null) { //调用构造方法创建bean的实例 //如果存在工厂方法则使用工厂方法进行初始化 //一个类有多个构造函数，每个构造函数都有不同的参数，所以需要根据参数锁定构造 函数并进行初始化。 //如果既不存在工厂方法也不存在带有参数的构造函数，则使用默认的构造函数进行 bean 的实例化 instanceWrapper = createBeanInstance(beanName, mbd, args); } final Object bean = (instanceWrapper != null ? instanceWrapper.getWrappedInstance() : null); Class<?> beanType = (instanceWrapper != null ? instanceWrapper.getWrappedClass() : null); mbd.resolvedTargetType = beanType; // Allow post-processors to modify the merged bean definition. synchronized (mbd.postProcessingLock) { if (!mbd.postProcessed) { try { //bean 合并后的处理， Autowired 注解正是通过此方法实现诸如类型的预解析。AutowiredAnnotationBeanPostProcessor
//会调用AutowiredAnnotationBeanPostProcessor的postProcessMergedBeanDefinition方法解析需要注入哪些对象
//然后在下面过程中的AutowiredAnnotationBeanPostProcessor.postProcessPropertyValues注入该对象 applyMergedBeanDefinitionPostProcessors(mbd, beanType, beanName); } catch (Throwable ex) { throw new BeanCreationException(mbd.getResourceDescription(), beanName, "Post-processing of merged bean definition failed", ex); } mbd.postProcessed = true; } } // Eagerly cache singletons to be able to resolve circular references // even when triggered by lifecycle interfaces like BeanFactoryAware. //判断当前bean是否需要暴露到 缓存对象中 //单例+允许循环依赖（默认的true）+bean正在创建 boolean earlySingletonExposure = (mbd.isSingleton() && this.allowCircularReferences && isSingletonCurrentlyInCreation(beanName)); if (earlySingletonExposure) { if (logger.isDebugEnabled()) { logger.debug("Eagerly caching bean '" + beanName + "' to allow for resolving potential circular references"); } //暴露早期对象到缓存中用于解决依赖 //把我们的早期对象包装成一个objectFactory对象 该对象提供了一个getObject方法,该方法内部调用getEarlyBeanReference方法 //早期对象存到三级缓存singletonFactories中去 //是在实例化之后在暴露出去的，所以循环依赖只能解决set注入的，对于构造注入的，循环依赖解决不了 addSingletonFactory(beanName, new ObjectFactory<Object>() { @Override public Object getObject() throws BeansException { return getEarlyBeanReference(beanName, mbd, bean); } }); } // Initialize the bean instance. Object exposedObject = bean; try { //初始化对象为当前的bean 填充属性，包括循环依赖的对象的注入 populateBean(beanName, mbd, instanceWrapper); if (exposedObject != null) {
//初始化调用实现initialBean接口和beanPostProcess方等法 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) { //去缓存中获取到我们的对象 由于传递的allowEarlyReference 是false 要求只能在一级二级缓存中去获取 //正常普通的bean(不存在循环依赖的bean) 创建的过程中，压根不会把三级缓存提升到二级缓存中 //所以这里获取到的都是空，因为加入到一级缓存中是在这个方法执行完后上叙的getSingleton(String beanName, ObjectFactory<?> singletonFactory)中 Object earlySingletonReference = getSingleton(beanName, false); if (earlySingletonReference != null) { if (exposedObject == bean) { exposedObject = earlySingletonReference; } else if (!this.allowRawInjectionDespiteWrapping && hasDependentBean(beanName)) { String[] dependentBeans = getDependentBeans(beanName); Set<String> actualDependentBeans = new LinkedHashSet<String>(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 " + "'getBeanNamesOfType' with the 'allowEagerInit' flag turned off, for example."); } } } } // Register bean as disposable. try { //注册 DisposableBean。 如果配置了 destroy-method，这里需要注册以便于在销毁时候调用 registerDisposableBeanIfNecessary(beanName, bean, mbd); } catch (BeanDefinitionValidationException ex) { throw new BeanCreationException( mbd.getResourceDescription(), beanName, "Invalid destruction signature", ex); } return exposedObject; }
6.1、populateBean(beanName, mbd, instanceWrapper)
protected void populateBean(String beanName, RootBeanDefinition mbd, BeanWrapper bw) { //从bean定义中获取属性列表 PropertyValues pvs = mbd.getPropertyValues(); //bw为空说明实例化失败，报错 if (bw == null) { if (!pvs.isEmpty()) { throw new BeanCreationException( mbd.getResourceDescription(), beanName, "Cannot apply property values to null instance"); } else { // Skip property population phase for null instance. return; } } // Give any InstantiationAwareBeanPostProcessors the opportunity to modify the // state of the bean before properties are set. This can be used, for example, // to support styles of field injection. boolean continueWithPropertyPopulation = true; //调用InstantiationAwareBeanPostProcessor的postProcessAfterInstantiation，只要有一个返回false,则停止循环 //可以向bean中注入自己的信息 if (!mbd.isSynthetic() && hasInstantiationAwareBeanPostProcessors()) { for (BeanPostProcessor bp : getBeanPostProcessors()) { if (bp instanceof InstantiationAwareBeanPostProcessor) { InstantiationAwareBeanPostProcessor ibp = (InstantiationAwareBeanPostProcessor) bp; if (!ibp.postProcessAfterInstantiation(bw.getWrappedInstance(), beanName)) { continueWithPropertyPopulation = false; break; } } } } //上面返回为flase 表示你已经通过自己写的InstantiationAwareBeanPostProcessor 类型的处理器已经设置过bean的属性值了 if (!continueWithPropertyPopulation) { return; } //判断注入模型是不是byName 或者是byType的 if (mbd.getResolvedAutowireMode() == RootBeanDefinition.AUTOWIRE_BY_NAME || mbd.getResolvedAutowireMode() == RootBeanDefinition.AUTOWIRE_BY_TYPE) { //封装属性列表 MutablePropertyValues newPvs = new MutablePropertyValues(pvs); // Add property values based on autowire by name if applicable. if (mbd.getResolvedAutowireMode() == RootBeanDefinition.AUTOWIRE_BY_NAME) { //按名称注入 autowireByName(beanName, mbd, bw, newPvs); } // Add property values based on autowire by type if applicable. if (mbd.getResolvedAutowireMode() == RootBeanDefinition.AUTOWIRE_BY_TYPE) { //按类型注入 autowireByType(beanName, mbd, bw, newPvs); } //把处理过的属性覆盖原来的 pvs = newPvs; } //判断有没有InstantiationAwareBeanPostProcessors处理器 boolean hasInstAwareBpps = hasInstantiationAwareBeanPostProcessors(); boolean needsDepCheck = (mbd.getDependencyCheck() != RootBeanDefinition.DEPENDENCY_CHECK_NONE); //用于在 Spring 填充属性到 bean 对象前，对属性的值进行相应的处理， //比如可以修改某些属性的值。这时注入到 bean 中的值就不是配置文件中的内容了， 而是经过后置处理器修改后的内容 if (hasInstAwareBpps || needsDepCheck) { PropertyDescriptor[] filteredPds = filterPropertyDescriptorsForDependencyCheck(bw, mbd.allowCaching); if (hasInstAwareBpps) { for (BeanPostProcessor bp : getBeanPostProcessors()) { if (bp instanceof InstantiationAwareBeanPostProcessor) { InstantiationAwareBeanPostProcessor ibp = (InstantiationAwareBeanPostProcessor) bp; //这里的AutowiredAnnotationBeanPostProcessor.postProcessPropertyValues会被调用 //如果有注解注入的，会调用这个方法注入注解的对象 pvs = ibp.postProcessPropertyValues(pvs, filteredPds, bw.getWrappedInstance(), beanName); if (pvs == null) { return; } } } } if (needsDepCheck) { checkDependencies(beanName, mbd, filteredPds, pvs); } } //设置属性到beanWapper中 applyPropertyValues(beanName, mbd, bw, pvs); }
6.2 initializeBean(final String beanName, final Object bean, RootBeanDefinition mbd)
protected Object initializeBean(final String beanName, final Object bean, RootBeanDefinition mbd) { if (System.getSecurityManager() != null) { AccessController.doPrivileged(new PrivilegedAction<Object>() { @Override public Object run() { invokeAwareMethods(beanName, bean); return null; } }, getAccessControlContext()); } else { //若我们的Bean实现了Aware接口进行方法的回调 invokeAwareMethods(beanName, bean); } Object wrappedBean = bean; if (mbd == null || !mbd.isSynthetic()) { //调用bean的后置处理器postProcessBeforeInitialization方法 wrappedBean = applyBeanPostProcessorsBeforeInitialization(wrappedBean, beanName); } try { //调用初始化方法，也是就是InitialzingBean与@PostConstruct invokeInitMethods(beanName, wrappedBean, mbd); } catch (Throwable ex) { throw new BeanCreationException( (mbd != null ? mbd.getResourceDescription() : null), beanName, "Invocation of init method failed", ex); } if (mbd == null || !mbd.isSynthetic()) { //调用bean的后置处理器postProcessAfterInitialization方法 wrappedBean = applyBeanPostProcessorsAfterInitialization(wrappedBean, beanName); } return wrappedBean; }
所以总结下调用顺序
1、BeanDefinitionRegistryPostProcessor.postProcessBeanDefinitionRegistry处理bean定义信息的
2、BeanFactoryPostProcessor.postProcessBeanFactory也是处理bean信息，
3、InstantiationAwareBeanPostProcessor.postProcessBeforeInstantiation实例化之前的处理
如果这里返回了bean，就会直接调用postProcessAfterInstantiation方法
4、调用构造函数反射创建空的bean对象（这时候创建的还是非代理对象）
5、暴露早期对象存到三级缓存singletonFactories中去
6、InstantiationAwareBeanPostProcessor.postProcessAfterInstantiation方法
7、InstantiationAwareBeanPostProcessor.postProcessPropertyValues修改属性
8、set赋值，注入属性
9、调用了我们的XXXAware接口进行回调
10、BeanPostProcessor.postProcessBeforeInitialization方法
11、InitializingBean.afterPropertiesSet方法
12、init-method或者@PostConstruct指定的方法
13、BeanPostProcessor.postProcessAfterInitialization方法（如果是代理对象，是在这里创建的）
14、注入单例缓存池singletonObjects中，删除二级缓存和三级缓存
总结下循环依赖
一级缓存 singletonObjects
二级缓存 earlySingletonObjects
三级缓存 singletonFactories
比如说A B 相互依赖
1、首先调用A的getBean()方法，创建A对象
2、调用调用构造函数反射创建空的bean对象A
3、暴露A的早期对象存到三级缓存singletonFactories中去（此时A还未被初始化），二级缓存earlySingletonObjects还没有值
4、会调用InstantiationAwareBeanPostProcessor.postProcessPropertyValues，AutowiredAnnotationBeanPostProcessor实现了该接口，所以会被调用，去生成A的属性B对象
5、调用B的getBean()方法
6、调用调用构造函数反射创建空的bean对象B
7、暴露B的早期对象存到三级缓存singletonFactories中去
8、会调用InstantiationAwareBeanPostProcessor.postProcessPropertyValues，AutowiredAnnotationBeanPostProcessor实现了该接口，所以会被调用，去获取A对象
9、调用A的getBean方法，然后调用getSingleton()方法，这时候会从从三级缓存中获取，也就是调用singletonFactories的getObject方法，返回A的早期对象，这时候会将A从三级缓存中删除，放入二级缓存中去
10、这时候就有了A对象，虽然没有初始化，但是不影响，然后调用B的初始化方法，生成B的完整对象，并将B对象放入一级缓存中，并删除二级三级缓存，B初始化完成
11、然后继续A的初始化，set注入B的对象，init方法等等
12、A初始化完成，放入一级缓存中
为什么要用三级缓存，两级不行吗
1、两级缓存是可以解决循环依赖的，但是解决不了aop代理，如果注入的对象实现了AOP，那么注入到其他bean的时候，不是最终的代理对象，而是原始的。通过三级缓存的ObjectFactory才能实现类最终的代理对象
我们看下三级缓存singletonFactories的getObject方法
addSingletonFactory(beanName, new ObjectFactory<Object>() { @Override public Object getObject() throws BeansException { return getEarlyBeanReference(beanName, mbd, bean); } }); protected Object getEarlyBeanReference(String beanName, RootBeanDefinition mbd, Object bean) { Object exposedObject = bean; if (bean != null && !mbd.isSynthetic() && hasInstantiationAwareBeanPostProcessors()) { for (BeanPostProcessor bp : getBeanPostProcessors()) { if (bp instanceof SmartInstantiationAwareBeanPostProcessor) { SmartInstantiationAwareBeanPostProcessor ibp = (SmartInstantiationAwareBeanPostProcessor) bp; exposedObject = ibp.getEarlyBeanReference(exposedObject, beanName); if (exposedObject == null) { return null; } } } } return exposedObject; }
可以看到实现了SmartInstantiationAwareBeanPostProcessor接口的类会在这里被调用
而AbstractAutoProxyCreator实现了getEarlyBeanReference（）方法，生成了代理类，保证了循环依赖注入的是代理类而不是原始类
AnnotationAwareAspectJAutoProxyCreator（实现aop）和InfrastructureAdvisorAutoProxyCreator(实现spring事务)都继承了AbstractAutoProxyCreator
所以二级缓存存的是循环依赖的代理类，三级缓存存的都是原始类
