SpringAop (四、AOP源码解析之获取 BeanDefinition 再之 applyBeanPostProcessorsAfterInitialization)

比眉伴天荒 2021-11-05 10:50 304阅读 0赞

上一篇[文章][Link 1]说完了`applyBeanPostProcessorsBeforeInitialization`，那么这篇文章说下`applyBeanPostProcessorsAfterInitialization`，也就是在Bean初始化完，调用的后置处理器。

# applyBeanPostProcessorsAfterInitialization #

@Override
    	public Object applyBeanPostProcessorsAfterInitialization(Object existingBean, String beanName)
    			throws BeansException {
    
    		Object result = existingBean;
    
    		// 同样获取createBean 过程中所有 BeanPostProcessors(bean后置处理器)
    		for (BeanPostProcessor beanProcessor : getBeanPostProcessors()) {
    			
    			// 重点 ：如果bean被子类标识为代理，则使用配置的拦截器创建一个代理。
    			Object current = beanProcessor.postProcessAfterInitialization(result, beanName);
    			if (current == null) {
    				return result;
    			}
    			result = current;
    		}
    		return result;
    	}

## postProcessAfterInitialization ##

@Override
    	public Object postProcessAfterInitialization(@Nullable Object bean, String beanName) throws BeansException {
    		if (bean != null) {
    			Object cacheKey = getCacheKey(bean.getClass(), beanName);
    			if (!this.earlyProxyReferences.contains(cacheKey)) {
    				
    				// 重点
    				return wrapIfNecessary(bean, beanName, cacheKey);
    			}
    		}
    		return bean;
    	}

### wrapIfNecessary ###

如果给定的bean符合被代理的条件，就将其包装起来。

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.
    		// 获取代理类，如果存在advice（增强）的话
    		Object[] specificInterceptors = getAdvicesAndAdvisorsForBean(bean.getClass(), beanName, null);
    		if (specificInterceptors != DO_NOT_PROXY) {
    			this.advisedBeans.put(cacheKey, Boolean.TRUE);
    			
    			// 重点：根据代理类创建代理。
    			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;
    	}

`getAdvicesAndAdvisorsForBean`方法最终会调用`AbstractAdvisorAutoProxyCreator#findEligibleAdvisors`方法：

#### findEligibleAdvisors ####

查找所有适合自动代理此类的合格advisor。

protected List<Advisor> findEligibleAdvisors(Class<?> beanClass, String beanName) {
    		
    		// 重点：查找自动代理中要使用的所有advisor。
    		List<Advisor> candidateAdvisors = findCandidateAdvisors();
    		
    		// 重点：在获取到的所有Advisor中，查找可应用于指定bean的所有顾问。
    		List<Advisor> eligibleAdvisors = findAdvisorsThatCanApply(candidateAdvisors, beanClass, beanName);
    		
    		extendAdvisors(eligibleAdvisors);
    		if (!eligibleAdvisors.isEmpty()) {
    			eligibleAdvisors = sortAdvisors(eligibleAdvisors);
    		}
    		return eligibleAdvisors;
    	}

##### findCandidateAdvisors() #####

该方法获取所有使用@Advisor的类，所以最终调用方法为：

advisors.add(this.beanFactory.getBean(name, Advisor.class));

这个就不细说了。

##### findAdvisorsThatCanApply #####

筛选bean。获取用于指定bean的

protected List<Advisor> findAdvisorsThatCanApply(
    			List<Advisor> candidateAdvisors, Class<?> beanClass, String beanName) {
    
    		ProxyCreationContext.setCurrentProxiedBeanName(beanName);
    		try {
    			
    			// 重点：调用AopUtils，
    			return AopUtils.findAdvisorsThatCanApply(candidateAdvisors, beanClass);
    		}
    		finally {
    			ProxyCreationContext.setCurrentProxiedBeanName(null);
    		}
    	}

**findAdvisorsThatCanApply**  
查找返回适用于给定类的 candidateAdvisors 列表的子列表。

public static List<Advisor> findAdvisorsThatCanApply(List<Advisor> candidateAdvisors, Class<?> clazz) {
    		if (candidateAdvisors.isEmpty()) {
    			return candidateAdvisors;
    		}
    		List<Advisor> eligibleAdvisors = new LinkedList<>();
    		for (Advisor candidate : candidateAdvisors) {
    			if (candidate instanceof IntroductionAdvisor && canApply(candidate, clazz)) {
    				eligibleAdvisors.add(candidate);
    			}
    		}
    		boolean hasIntroductions = !eligibleAdvisors.isEmpty();
    		for (Advisor candidate : candidateAdvisors) {
    			if (candidate instanceof IntroductionAdvisor) {
    				// already processed
    				continue;
    			}
    
    			// 重点，canApply方法
    			if (canApply(candidate, clazz, hasIntroductions)) {
    				eligibleAdvisors.add(candidate);
    			}
    		}
    		return eligibleAdvisors;
    	}

遍历被代理类的所有的方法，跟进切面表达式进行匹配，如果有一个方法匹配到，也就意味着该类会被代理。  
匹配方法是借助org.aspectj.weaver.internal.tools实现，也就是AspectJ框架中的工具类，有兴趣的可以自行查看。

#### createProxy ####

获取给定`bean`

protected Object createProxy(Class<?> beanClass, @Nullable String beanName,
    			@Nullable Object[] specificInterceptors, TargetSource targetSource) {
    
    		if (this.beanFactory instanceof ConfigurableListableBeanFactory) {
    			AutoProxyUtils.exposeTargetClass((ConfigurableListableBeanFactory) this.beanFactory, beanName, beanClass);
    		}
    
    		ProxyFactory proxyFactory = new ProxyFactory();
    		proxyFactory.copyFrom(this);
    
    		if (!proxyFactory.isProxyTargetClass()) {
    			if (shouldProxyTargetClass(beanClass, beanName)) {
    				proxyFactory.setProxyTargetClass(true);
    			}
    			else {
    				evaluateProxyInterfaces(beanClass, proxyFactory);
    			}
    		}
    
    		Advisor[] advisors = buildAdvisors(beanName, specificInterceptors);
    		proxyFactory.addAdvisors(advisors);
    		proxyFactory.setTargetSource(targetSource);
    		customizeProxyFactory(proxyFactory);
    
    		proxyFactory.setFrozen(this.freezeProxy);
    		if (advisorsPreFiltered()) {
    			proxyFactory.setPreFiltered(true);
    		}
    
    		return proxyFactory.getProxy(getProxyClassLoader());
    	}

**getProxy**  
`getProxy`最终会调用`DefaultAopProxyFactory#createAopProxy`方法  
所以：

@Override
    	public AopProxy createAopProxy(AdvisedSupport config) throws AopConfigException {
    		if (config.isOptimize() || config.isProxyTargetClass() || hasNoUserSuppliedProxyInterfaces(config)) {
    			Class<?> targetClass = config.getTargetClass();
    			if (targetClass == null) {
    				throw new AopConfigException("TargetSource cannot determine target class: " +
    						"Either an interface or a target is required for proxy creation.");
    			}
    			
    			// //如果代理目标是接口或者Proxy类型，则走jdk代理
    			if (targetClass.isInterface() || Proxy.isProxyClass(targetClass)) {
    				return new JdkDynamicAopProxy(config);
    			}
    			return new ObjenesisCglibAopProxy(config);
    		}
    		else {
    			return new JdkDynamicAopProxy(config);
    		}
    	}

该方法通过三个变量来进行筛选代理方法：

*  optimize：官方文档翻译为设置代理是否应执行积极的优化，默认为false。
 *  proxyTargetClass：这个在上面已经提到了，AopAutoConfiguration中指定，默认为true，也就是选择使用 cglib 代理。可以看到该变量和optimize意义一样，之所以这么做，个人理解是为了可以在不同的场景中使用。
 *  hasNoUserSuppliedProxyInterfaces：是否设置了实现接口。

**hasNoUserSuppliedProxyInterfaces**方法

确定提供的 advisedsupport 是否指定了 org.springframework.aop.springproxy接口（或者根本没有指定代理接口）。

private boolean hasNoUserSuppliedProxyInterfaces(AdvisedSupport config) {
    		Class<?>[] ifcs = config.getProxiedInterfaces();
    		return (ifcs.length == 0 || (ifcs.length == 1 && SpringProxy.class.isAssignableFrom(ifcs[0])));
    	}

# UML图： #

![uml][]

# 流程图： #

![流程图][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2phdmFfeWVz_size_16_color_FFFFFF_t_70]

# 总结 #

相对于前置处理，后置处理就要简单很多了

1.  返回是否要代理给定的bean、要应用的附加建议（例如AOP联盟拦截器）和顾问。
2.  创建代理类。

[Link 1]: https://blog.csdn.net/java_yes/article/details/98209495
[uml]: /images/20211105/b320601a52154b29977476c20a756f88.png
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2phdmFfeWVz_size_16_color_FFFFFF_t_70]: /images/20211105/5ad39148ae0443888675fd0af9eeda9c.png