Spring的循环依赖和三级缓存

@Data
public class A {
  private B b;
  public A() {System.out.println("A 无参构造器。。。");}
  public void speak() {System.out.println("------AAA---------");}
}

@Data
public class B {
  public B() {System.out.println("B 无参构造器。。。");}
  private A a;
  public void speak() {System.out.println("------BBB---------");}
}

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

		// Instantiate the bean.
		BeanWrapper instanceWrapper = null;
		if (mbd.isSingleton()) {
			//省略
		}
		if (instanceWrapper == null) {
		    //1)调用无参构造方法创建Bean
			instanceWrapper = createBeanInstance(beanName, mbd, args);
		}
		final Object bean = instanceWrapper.getWrappedInstance();
		Class<?> beanType = instanceWrapper.getWrappedClass();
		if (beanType != NullBean.class) {
			mbd.resolvedTargetType = beanType;
		}

		
		synchronized (mbd.postProcessingLock) {
			//省略
		}

		
		boolean earlySingletonExposure = (mbd.isSingleton() && this.allowCircularReferences &&
				isSingletonCurrentlyInCreation(beanName));
		if (earlySingletonExposure) {
			if (logger.isTraceEnabled()) {
				//省略
			}
			//2)把该bean对象添加到三级缓存中，注意getEarlyBeanReference方法，特别有用
			addSingletonFactory(beanName, () -> getEarlyBeanReference(beanName, mbd, bean));
		}

		// Initialize the bean instance.
		Object exposedObject = bean;
		try {
		    //3)Bean的属性赋值
			populateBean(beanName, mbd, instanceWrapper);
			//4)处理aware接口、applyBeanPostProcessorsBeforeInitialization、initMethod
			exposedObject = initializeBean(beanName, exposedObject, mbd);
		}
		catch (Throwable ex) {
			if (ex instanceof BeanCreationException && beanName.equals(((BeanCreationException) ex).getBeanName())) {
				//省略
			}
			else {
				//省略
			}
		}

		if (earlySingletonExposure) {
			//省略
		}

		// Register bean as disposable.
		try {
			registerDisposableBeanIfNecessary(beanName, bean, mbd);
		}
		catch (BeanDefinitionValidationException ex) {
			//省略
		}

		return exposedObject;
	}





}

//DefaultSingletonBeanRegistry
protected Object getSingleton(String beanName, boolean allowEarlyReference) {
        //从一级缓存中获取，即IOC容器，即完整的Bean对象
		Object singletonObject = this.singletonObjects.get(beanName);
		if (singletonObject == null && isSingletonCurrentlyInCreation(beanName)) {
			synchronized (this.singletonObjects) {
                //从二级缓存中获取
				singletonObject = this.earlySingletonObjects.get(beanName);
				if (singletonObject == null && allowEarlyReference) {
                    //从三级缓存中获取
					ObjectFactory<?> singletonFactory = this.singletonFactories.get(beanName);
					if (singletonFactory != null) {
						singletonObject = singletonFactory.getObject();
						this.earlySingletonObjects.put(beanName, singletonObject);
						this.singletonFactories.remove(beanName);
					}
				}
			}
		}
		return singletonObject;
	}

protected Object getEarlyBeanReference(String beanName, RootBeanDefinition mbd, Object bean) {
		Object exposedObject = bean;
		if (!mbd.isSynthetic() && hasInstantiationAwareBeanPostProcessors()) {
			for (BeanPostProcessor bp : getBeanPostProcessors()) {
				if (bp instanceof SmartInstantiationAwareBeanPostProcessor) {
					SmartInstantiationAwareBeanPostProcessor ibp = (SmartInstantiationAwareBeanPostProcessor) bp;
					exposedObject = ibp.getEarlyBeanReference(exposedObject, beanName);
				}
			}
		}
		return exposedObject;
	}

//AbstractAutoProxyCreator
@Override
	public Object getEarlyBeanReference(Object bean, String beanName) {
		Object cacheKey = getCacheKey(bean.getClass(), beanName);
		this.earlyProxyReferences.put(cacheKey, bean);
        //跟进去
		return wrapIfNecessary(bean, beanName, cacheKey);
	}

//AbstractAutoProxyCreator
protected Object wrapIfNecessary(Object bean, String beanName, Object cacheKey) {
		if (StringUtils.hasLength(beanName) && this.targetSourcedBeans.contains(beanName)) {
			return bean;
		}
		if (Boolean.FALSE.equals(this.advisedBeans.get(cacheKey))) {
			return bean;
		}
		if (isInfrastructureClass(bean.getClass()) || shouldSkip(bean.getClass(), beanName)) {
			this.advisedBeans.put(cacheKey, Boolean.FALSE);
			return bean;
		}

		// Create proxy if we have advice.
		Object[] specificInterceptors = getAdvicesAndAdvisorsForBean(bean.getClass(), beanName, null);
		if (specificInterceptors != DO_NOT_PROXY) {
			this.advisedBeans.put(cacheKey, Boolean.TRUE);
            //返回了一个新对象，新地址
            //返回了一个新对象，新地址
            //返回了一个新对象，新地址
			Object proxy = createProxy(
					bean.getClass(), beanName, specificInterceptors, new SingletonTargetSource(bean));
			this.proxyTypes.put(cacheKey, proxy.getClass());
			return proxy;
		}

		this.advisedBeans.put(cacheKey, Boolean.FALSE);
		return bean;
	}

//AbstractAutowireCapableBeanFactory
protected Object doCreateBean{
//创建A
Object exposedObject = bean;
		try {
            //初始化A,因为A中有属性B，此时去创建B，然后把A的代理对象存入earlySingletonObjects缓存中，B创建完毕，然后又回到此处继续初始化A
			populateBean(beanName, mbd, instanceWrapper);
            //为非代理对象A执行aware接口等等
			exposedObject = initializeBean(beanName, exposedObject, mbd);
		}
		catch (Throwable ex) {
			//省略
			}
		}

		if (earlySingletonExposure) {
            //在earlySingletonObjects中拿到代理对象A
			Object earlySingletonReference = getSingleton(beanName, false);
			if (earlySingletonReference != null) {
				if (exposedObject == bean) {
                    //把exposedObject由指向非代理对象A变为指向代理对象A,那么
                    //exposedObject = initializeBean(beanName, exposedObject, mbd);
                    //我认为是白做了，我不清楚这个地方？？？？？？？？？？？？？？？
					exposedObject = earlySingletonReference;
				}
				else if (!this.allowRawInjectionDespiteWrapping && hasDependentBean(beanName)) {
					String[] dependentBeans = getDependentBeans(beanName);
					Set<String> 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 " +
								"'getBeanNamesOfType' with the 'allowEagerInit' flag turned off, for example.");
					}
				}
			}

}