前言

在這篇文章里，最后總結(jié)處，我說了會講講循環(huán)依賴中，其中一個類添加@Async有可能會導(dǎo)致注入失敗而拋異常的情況，今天就分析一下。

一、異常表現(xiàn)，拋出內(nèi)容

1.1循環(huán)依賴的兩個class

1.CycleService1

@Service
public class CycleService1 {

	@Autowired
	private CycleService2 cycleService2;

	@WangAnno
	@Async
	public void doThings() {
		System.out.println("it's a async move");
	}

}

2.CycleService2

@Service
public class CycleService2 {

	private CycleService1 cycleService1;

	public void init() {

	}

	@WangAnno
	public void alsoDo() {
		System.out.println("create cycleService2");
	}

}

1.2 啟動報錯

Bean with name ‘cycleService1' has been injected into other beans [cycleService2] 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.

警告: Exception encountered during context initialization - cancelling refresh attempt: org.springframework.beans.factory.BeanCurrentlyInCreationException: Error creating bean with name 'cycleService1': Bean with name 'cycleService1' has been injected into other beans [cycleService2] 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.

Exception in thread "main" org.springframework.beans.factory.BeanCurrentlyInCreationException: Error creating bean with name 'cycleService1': Bean with name 'cycleService1' has been injected into other beans [cycleService2] 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.

at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:654)

at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:523)

at org.springframework.beans.factory.support.AbstractBeanFactory.lambda$doGetBean$0(AbstractBeanFactory.java:323)

at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:226)

at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:320)

at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:199)

at org.springframework.beans.factory.support.DefaultListableBeanFactory.preInstantiateSingletons(DefaultListableBeanFactory.java:851)

at org.springframework.context.support.AbstractApplicationContext.finishBeanFactoryInitialization(AbstractApplicationContext.java:884)

at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:552)

at com.wang.Test.main(Test.java:109)

二、原因分析

2.1 主要原因

想想我在這篇博客里的圖解步驟：

1. 當Spring在進行bean的實例化的時候，由于CycleService1和CycleService2是循環(huán)依賴的，
2. 同時，由于CycleService1創(chuàng)建早于CycleService2。
3. 所以，在CycleService1對CycleService2的initializeBean方法執(zhí)行之后得到了exposedObject，要從二級緩存里獲取CycleService1的earlySingletonReference不為null，就需要比較exposedObject和raw CycleService是否還是同一個對象，如果不再是同一個對象，那么就會報錯。
4. 為什么有這個邏輯呢？
5. 其實是因為如果能從二級緩存里拿出的earlySingletonReference不為null，說明了在該對象再創(chuàng)建過程中被其他對象循環(huán)依賴了，且調(diào)用了三級工廠中該對象的ObjectFactory方法，基于raw bean生成了對象放入到了二級緩存。但是當raw bean執(zhí)行完initializeBean之后生成了新的對象，那就出問題了。如下圖：

也就是說基于raw bean，得到了兩個基于該raw bean生成的proxy對象，Spring容器不知道最終該在容器里保存哪一個了。

2.2 循環(huán)依賴放入二級緩存處邏輯

1.每個bean在進行屬性注入之前，默認都會往Spring容器中放入一個ObjectFactory進入三級工廠，以便自己在屬性注入的時候被循環(huán)依賴時調(diào)用生成對象

if (earlySingletonExposure) {
	// 返回一個進行了aop處理的ObjectFactory，提前暴露
	// 但是只有當該實例在創(chuàng)建過程中還被其他實例引用（循環(huán)依賴），才會被調(diào)用getEarlyBeanReference
	// 此處是第四次調(diào)用beanPostProcessor，不一定會調(diào)用，只有當該類真的在創(chuàng)建過程中被其他類當做屬性所依賴
	addSingletonFactory(beanName, () -> getEarlyBeanReference(beanName, mbd, bean));
}

2.所以在創(chuàng)建CycleService1過程中，CycleService2去注入CycleService2之前在三級工廠里放入了自己的ObjectFactory對象，然后在CycleService2創(chuàng)建過程中，要注入CycleService1的時候，就會調(diào)用Spring容器中的getEarlyBeanReference(beanName, mbd, bean)獲取CycleService1，下面我們來看看該方法調(diào)用的具體邏輯

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;
	}

然后咱們debug發(fā)現(xiàn)，只有AbstractAutoProxyCreator#getEarlyBeanReference方法，有具體實現(xiàn)邏輯

public Object getEarlyBeanReference(Object bean, String beanName) {
		Object cacheKey = getCacheKey(bean.getClass(), beanName);
		this.earlyProxyReferences.put(cacheKey, bean);
		return wrapIfNecessary(bean, beanName, cacheKey);
	}

具體的細節(jié)，我們就不進入的，主要就是通過調(diào)用wrapIfNecessary生成了raw bean的aop proxy bean，后面放入了二級緩存。

2.3 initializeBean生成的對象

在initializeBean方法里會調(diào)用applyBeanPostProcessorsAfterInitialization方法

@Override
	public Object applyBeanPostProcessorsAfterInitialization(Object existingBean, String beanName)
			throws BeansException {

		Object result = existingBean;
		for (BeanPostProcessor processor : getBeanPostProcessors()) {
			Object current = processor.postProcessAfterInitialization(result, beanName);
			if (current == null) {
				return result;
			}
			result = current;
		}
		return result;
	}

在循環(huán)里面會調(diào)用postProcessAfterInitialization方法
重點關(guān)注AbstractAutoProxyCreator的該方法實現(xiàn)：

@Override
	public Object postProcessAfterInitialization(@Nullable Object bean, String beanName) {
		if (bean != null) {
			Object cacheKey = getCacheKey(bean.getClass(), beanName);
			if (this.earlyProxyReferences.remove(cacheKey) != bean) {
				// 對bean進行proxy操作
				return wrapIfNecessary(bean, beanName, cacheKey);
			}
		}
		return bean;
	}

會發(fā)現(xiàn)AbstractAutoProxyCreator#postProcessAfterInitialization里面的具體邏輯就是判斷這個類有沒有調(diào)用過wrapIfNecessary，如果調(diào)用過就不再調(diào)用，就是保證同一個raw bean不會被多次proxy，同時提前暴露注入到其他對象里的就是proxy bean。
但是由于該bean（CycleService1）上加了@Async注解，此次也會觸發(fā)AsyncAnnotationBeanPostProcessor#postProcessAfterInitialization，而這個方法，我們在這篇文章里講過了，正是@Async注解能生效的關(guān)鍵邏輯。所以此處生成了一個具有Async功能的新的async proxy bean

2.4 再次分析原因

基于2.3和2.4，我們基于raw bean得到了二級緩存里的aop proxy bean和async proxy bean。
讓我們再回憶一下判斷邏輯：

//此處是從二級緩存里面根據(jù)beanName拿出對象，因為二級緩存里放入的是因為循環(huán)依賴給其他bean注入的代理對象
	Object earlySingletonReference = getSingleton(beanName, false);
	if (earlySingletonReference != null) {
		if (exposedObject == bean) {
			exposedObject = earlySingletonReference;
		}
		// 我們之前早期暴露出去的Bean跟現(xiàn)在最后要放到容器中的Bean不是同一個
		// allowRawInjectionDespiteWrapping為false
		// 并且當前Bean被當成依賴注入到了別的Bean中
		else if (!this.allowRawInjectionDespiteWrapping && hasDependentBean(beanName)) {
			// 獲取到當前Bean依賴的Bean
			String[] dependentBeans = getDependentBeans(beanName);
			// 要得到真實的依賴的Bean
			Set<String> actualDependentBeans = new LinkedHashSet<>(dependentBeans.length);
			for (String dependentBean : dependentBeans) {
				// 移除那些僅僅為了類型檢查而創(chuàng)建出來
				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.");
			}
		}
	}

簡而言之，也就是此時從二級緩存里拿到了aop proxy bean，同時了執(zhí)行完initializeBean之后，raw bean變?yōu)榱薬sync proxybean，Spring容器基于raw bean得到了兩個proxy bean，無法處理了。所以在使用@Async注解時，盡量不要在被循環(huán)依賴的Class上添加

解決方案

打破循環(huán)依賴

目前我能想到的方法就是打破循環(huán)依賴，因為循環(huán)依賴發(fā)生在bean生命周期的–屬性注入階段，所以我們需要做的就是打破這種循環(huán)依賴

1.延遲注入（使用@Lazy注解）

@Service
public class CycleService1 {

	@Lazy
	@Autowired
	private CycleService2 cycleService2;

	@WangAnno
	@Async
	public void doThings() {
		cycleService2.alsoDo();
		System.out.println("it's a async move");
	}

}

看過這篇文章的都知道原理了，此處不再累贅

2. 手動延遲注入（使用applicationContext.getBean）

@Service
public class CycleService1 {

	@Autowired
	private ApplicationContext applicationContext;

	private CycleService2 cycleService2;

	@WangAnno
	@Async
	public void doThings() {
		if (Objects.isNull(cycleService2)) {
			cycleService2 = applicationContext.getBean(CycleService2.class);
		}
		cycleService2.alsoDo();
		System.out.println("it's a async move");
	}

}

其實效果是上面加了@Lazy效果是一樣的，不過是我們自己在方法執(zhí)行的過程中手動進行延遲注入而已。

總結(jié)

從二級緩存里拿到earlySingletonReference（aop proxy bean），同時了執(zhí)行完initializeBean之后，raw bean變?yōu)榱薳xposedObject（async proxy bean），Spring容器基于raw bean得到了兩個proxy bean，無法處理了。
所以在使用@Async注解時，盡量不要在被循環(huán)依賴的Class上添加
實在非要添加，可以看看我給出的解決方法。

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