AOP源码笔记

AOP源码笔记

在创建对象doCreateBean方法里面，执行完依赖注入populateBean方法以后，在initializeBean方法中进行AOP增强：

		try {
			populateBean(beanName, mbd, instanceWrapper);
			exposedObject = initializeBean(beanName, exposedObject, mbd);
		}

通过调用AbstractAutoProxyCreator的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;
	}

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

调用wrapIfNecessary方法返回代理对象

		Object[] specificInterceptors = getAdvicesAndAdvisorsForBean(bean.getClass(), beanName, null);
		if (specificInterceptors != DO_NOT_PROXY) {
			this.advisedBeans.put(cacheKey, Boolean.TRUE);
			Object proxy = createProxy(
					bean.getClass(), beanName, specificInterceptors, new SingletonTargetSource(bean));
			this.proxyTypes.put(cacheKey, proxy.getClass());
			return proxy;
		}

关键看Object[] specificInterceptors 这个东西是什么，查看getAdvicesAndAdvisorsForBean方法：

	@Override
	@Nullable
	protected Object[] getAdvicesAndAdvisorsForBean(
			Class beanClass, String beanName, @Nullable TargetSource targetSource) {

		List advisors = findEligibleAdvisors(beanClass, beanName);
		if (advisors.isEmpty()) {
			return DO_NOT_PROXY;
		}
		return advisors.toArray();
	}

这里返回了一个Advisor的List:advisors ,可以理解为这些需要给对象增强的一个个通知

	protected List findEligibleAdvisors(Class beanClass, String beanName) {
		List candidateAdvisors = findCandidateAdvisors();
		List eligibleAdvisors = findAdvisorsThatCanApply(candidateAdvisors, beanClass, beanName);
		extendAdvisors(eligibleAdvisors);
		if (!eligibleAdvisors.isEmpty()) {
			eligibleAdvisors = sortAdvisors(eligibleAdvisors);
		}
		return eligibleAdvisors;
	}

findEligibleAdvisors包含有3个方法，第一个方法是寻找所有的切面的通知（如果是第一次，会解析配置类，将切面的通知都缓存起来，第二个方法是筛选出匹配这个对象的通知列表，第三个是advisors.add(0, ExposeInvocationInterceptor.ADVISOR)加上ExposeInvocationInterceptor拦截器。

specificInterceptors 就是可以理解为一个拦截器的列表，每个拦截器都封装了拦截后执行的方法，以及这个拦截器拦截的类型（before，after等等）

接下来就可以看创建代理类的方法了

			Object proxy = createProxy(
					bean.getClass(), beanName, specificInterceptors, new SingletonTargetSource(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());
	}			

可以看到proxyFactory持有了advisors，targetSource这些对象，然后调用getProxy的方法

	public Object getProxy(@Nullable ClassLoader classLoader) {
		return createAopProxy().getProxy(classLoader);
	}

createAopProxy方法其实就是选择用jdk的动态代理还是cglib的动态代理：

	@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.");
			}
			if (targetClass.isInterface() || Proxy.isProxyClass(targetClass)) {
				return new JdkDynamicAopProxy(config);
			}
			return new ObjenesisCglibAopProxy(config);
		}
		else {
			return new JdkDynamicAopProxy(config);
		}
	}

最终调用getProxy方法其实就是在调用JdkDynamicAopProxy或者ObjenesisCglibAopProxy的getProxy方法，先看jdk的动态代理方法

	@Override
	public Object getProxy(@Nullable ClassLoader classLoader) {
		if (logger.isTraceEnabled()) {
			logger.trace("Creating JDK dynamic proxy: " + this.advised.getTargetSource());
		}
		Class[] proxiedInterfaces = AopProxyUtils.completeProxiedInterfaces(this.advised, true);
		findDefinedEqualsAndHashCodeMethods(proxiedInterfaces);
		return Proxy.newProxyInstance(classLoader, proxiedInterfaces, this);
	}

根据jdk动态代理的方法，当调用接口的方法时，其实会走到动态代理h对象的invoke方法里面去，可以看一下JdkDynamicAopProxy的invoke方法

public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
			// Get the interception chain for this method.
			List