spring多个动态代理导致循环依赖报错问题解决

项目里需要对方法进行监控，记录执行时间超长的方法。很自然会想用到AOP动态代理加强方式来解决。于是呼就了下面的代码，下面的是测试代码(项目代码不好贴)，有需要测试代码的，可下载附件：

DemoMethodInterceptor类：

public class DemoMethodInterceptor implements MethodInterceptor {

    @Override
    public Object invoke(MethodInvocation invocation) throws Throwable {
        System.out.println("invoke start...");
        return invocation.proceed();
    }

}

spring配置：

<bean id="demoMethodInterceptor" class="name.zhengwei.demo.spring.aop.DemoMethodInterceptor">
	</bean>

	<bean class="org.springframework.aop.framework.autoproxy.BeanNameAutoProxyCreator">
		<property name="beanNames">
			<value>class*</value>
		</property>
		<property name="interceptorNames">
			<list>
				<value>demoMethodInterceptor</value>
			</list>
		</property>
	</bean>

这里用spring的BeanNameAutoProxyCreator来对以'class'作为前缀的bean做动态代理。结果抛出了异常，如下：

Error creating bean with name 'classA': Bean with name 'classA' has been injected into other beans [classB] 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.

从提示看是非最终版本的classA被注入到了循环依赖的classB里，但spring是支持循环依赖的啊，而且在代码里不可避免会有这种情况出现，那为什么会出现非最终版本被注入呢？经过debug发现答案在，spring的‘AbstractAutowireCapableBeanFactory’的getEarlyBeanReference方法里（[color=red]我的spring版本是3.0.1-release[/color]）。

/**
	 * Obtain a reference for early access to the specified bean,
	 * typically for the purpose of resolving a circular reference.
	 * @param beanName the name of the bean (for error handling purposes)
	 * @param mbd the merged bean definition for the bean
	 * @param bean the raw bean instance
	 * @return the object to expose as bean reference
	 */
	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;
	}

如果spring设置为支持循环依赖(默认支持)，那么在创建的时候，如果有循环依赖发生，就会执行上面这段代码。在DEBUG的时候发现了2个代理创建类，也就是InfrastructureAdvisorAutoProxyCreator（项目里用了spring-security）和BeanNameAutoProxyCreator，这两个类都会执行各自的getEarlyBeanReference方法，都来自父类AbstractAutoProxyCreator。

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

getEarlyBeanReference方法会缓存创建的代理对象，在各自this.earlyProxyReferences里，两个类都会创建代理，因此有了2个代理对象，前者先执行（InfrastructureAdvisorAutoProxyCreator），假设对象分别得proxy1和proxy2，最终proxy2又代理了proxy1，那么执行完后，返回的是proxy2对象。

接下来的关键点是在bean生命周期里的后置处理器了，BeanPostProcessor是对bean的最后一次加强。跟踪代码，spring会执行下面这段代码，AbstractAutoProxyCreator的postProcessAfterInitialization方法，InfrastructureAdvisorAutoProxyCreator和BeanNameAutoProxyCreator都是一种BeanPostProcessor，因此会执行2次，顺序跟执行getEarlyBeanReference方法一致，前者先执行：

/**
	 * Create a proxy with the configured interceptors if the bean is
	 * identified as one to proxy by the subclass.
	 * @see #getAdvicesAndAdvisorsForBean
	 */
	public Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException {
		if (bean != null) {
			Object cacheKey = getCacheKey(bean.getClass(), beanName);
			if (!this.earlyProxyReferences.contains(cacheKey)) {
				return wrapIfNecessary(bean, beanName, cacheKey);
			}
		}
		return bean;
	}

这里又会执行2次？为什么呢？因为前面的getEarlyBeanReference方法执行2次后，后面的对象proxy2代理了proxy1。这里传入的bean还是原生对象，第一次执行的时候还是正确的，但第2次执行时(也就是BeanNameAutoProxyCreator)就会出现问题，因为之前earlyProxyReferences里保存的是对proxy1对象的创建状态，而传入的bean还是原生对象，那么显然是没有的，因此又有了对象proxy3，这个proxy3返回后，赋值给了变量'exposedObject '，如下：

// Initialize the bean instance.
		Object exposedObject = bean;
		try {
			populateBean(beanName, mbd, instanceWrapper);
			if (exposedObject != null) {
				exposedObject = initializeBean(beanName, exposedObject, mbd);
			}
		}

接下来是异常抛出的地点了：

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<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.");
					}
				}
			}
		}

上面第2行代码的earlySingletonReference=proxy2，exposedObject=proxy3，bean=原始的bean对象，因此结局就有了最上面的异常。


[size=large][color=red]我的解决方法：[/color][/size]
[color=red]解决方法是不用BeanNameAutoProxyCreator，改用<aop:config>。[/color]

<bean id="methodProfileAdvice" class="name.zhengwei.demo.spring.aop.MethodProfileAdvice"></bean>

<!-- 进行aop配置 -->
	<aop:config proxy-target-class="false">	
	  <!-- 配置日志切面 -->
	  <aop:aspect id="methodProfileAspect" ref="methodProfileAdvice">	 	  

	    <aop:pointcut id="methodProfilePointcut" expression="execution(* name.zhengwei.demo.spring.service..*.*(..))" />

	    <!-- 将methodProfileAdvice通知中的方法指定为环绕通知 -->
	    <aop:around method="myAroundAdvice" pointcut-ref="methodProfilePointcut"/>
	  </aop:aspect>
	</aop:config>

[size=large][color=red]原因：[/color][/size]
因为在解析的时候会判断是否已经存在InfrastructureAdvisorAutoProxyCreator，AspectJAwareAdvisorAutoProxyCreator，AnnotationAwareAspectJAutoProxyCreator三者之一，有就合并，否则就注册一个，因此始终就只会有一个代理创建器。
<aop:config>会交给org.springframework.aop.config.AopNamespaceHandler处理

registerBeanDefinitionParser("config", new ConfigBeanDefinitionParser());

ConfigBeanDefinitionParser的parse方法会解析配置：

public BeanDefinition parse(Element element, ParserContext parserContext) {
		CompositeComponentDefinition compositeDef =
				new CompositeComponentDefinition(element.getTagName(), parserContext.extractSource(element));
		parserContext.pushContainingComponent(compositeDef);

		configureAutoProxyCreator(parserContext, element);

		NodeList childNodes = element.getChildNodes();
		for (int i = 0; i < childNodes.getLength(); i++) {
			Node node = childNodes.item(i);
			if (node.getNodeType() == Node.ELEMENT_NODE) {
				String localName = parserContext.getDelegate().getLocalName(node);
				if (POINTCUT.equals(localName)) {
					parsePointcut((Element) node, parserContext);
				}
				else if (ADVISOR.equals(localName)) {
					parseAdvisor((Element) node, parserContext);
				}
				else if (ASPECT.equals(localName)) {
					parseAspect((Element) node, parserContext);
				}
			}
		}

		parserContext.popAndRegisterContainingComponent();
		return null;
	}

看其中的configureAutoProxyCreator方法，会委托给AopNamespaceUtils的registerAspectJAutoProxyCreatorIfNecessary方法处理：

/**
	 * Configures the auto proxy creator needed to support the {@link BeanDefinition BeanDefinitions}
	 * created by the '<code><aop:config/></code>' tag. Will force class proxying if the
	 * '<code>proxy-target-class</code>' attribute is set to '<code>true</code>'.
	 * @see AopNamespaceUtils
	 */
	private void configureAutoProxyCreator(ParserContext parserContext, Element element) {
		AopNamespaceUtils.registerAspectJAutoProxyCreatorIfNecessary(parserContext, element);
	}

AopNamespaceUtils的registerAspectJAutoProxyCreatorIfNecessary方法：

public static void registerAspectJAutoProxyCreatorIfNecessary(
			ParserContext parserContext, Element sourceElement) {

		BeanDefinition beanDefinition = AopConfigUtils.registerAspectJAutoProxyCreatorIfNecessary(
				parserContext.getRegistry(), parserContext.extractSource(sourceElement));
		useClassProxyingIfNecessary(parserContext.getRegistry(), sourceElement);
		registerComponentIfNecessary(beanDefinition, parserContext);
	}

AopConfigUtils的registerAspectJAutoProxyCreatorIfNecessary方法：

public static BeanDefinition registerAspectJAutoProxyCreatorIfNecessary(BeanDefinitionRegistry registry, Object source) {
		return registerOrEscalateApcAsRequired(AspectJAwareAdvisorAutoProxyCreator.class, registry, source);
	}

registerOrEscalateApcAsRequired方法：

private static BeanDefinition registerOrEscalateApcAsRequired(Class cls, BeanDefinitionRegistry registry, Object source) {
		Assert.notNull(registry, "BeanDefinitionRegistry must not be null");
		if (registry.containsBeanDefinition(AUTO_PROXY_CREATOR_BEAN_NAME)) {
			BeanDefinition apcDefinition = registry.getBeanDefinition(AUTO_PROXY_CREATOR_BEAN_NAME);
			if (!cls.getName().equals(apcDefinition.getBeanClassName())) {
				int currentPriority = findPriorityForClass(apcDefinition.getBeanClassName());
				int requiredPriority = findPriorityForClass(cls);
				if (currentPriority < requiredPriority) {
					apcDefinition.setBeanClassName(cls.getName());
				}
			}
			return null;
		}
		RootBeanDefinition beanDefinition = new RootBeanDefinition(cls);
		beanDefinition.setSource(source);
		beanDefinition.getPropertyValues().add("order", Ordered.HIGHEST_PRECEDENCE);
		beanDefinition.setRole(BeanDefinition.ROLE_INFRASTRUCTURE);
		registry.registerBeanDefinition(AUTO_PROXY_CREATOR_BEAN_NAME, beanDefinition);
		return beanDefinition;
	}

上面代码，判断是否存在id='org.springframework.aop.config.internalAutoProxyCreator'的bean，否则注册一个，如果有，那么进行合并。

参考：
http://jinnianshilongnian.iteye.com/blog/1901694 阅读更多