[Java知识库]SpringAop代理模式底层核心源码分析

aop核心的bean是什么？
一般情况会使用@EnableAspectJAutoProxy注解来使Aop注入到我们Spring的IoC容器中，那这个注入的类是啥呢
测试代码如下

@Configuration
@EnableAspectJAutoProxy
public class MyConfig {
}
    public static void main(String[] args) {
        AnnotationConfigApplicationContext context = new AnnotationConfigApplicationContext(MyConfig.class);
        String[] strings = context.getBeanDefinitionNames();
        for(String s : strings){
            System.out.println("name:"+s);
        }
    }

通过这个注解，把aop核心注入到ioc容器中，此时看看bean的路径是啥，
控制台输出结果如下所示

name:org.springframework.context.annotation.internalConfigurationAnnotationProcessor
name:org.springframework.context.annotation.internalAutowiredAnnotationProcessor
name:org.springframework.context.annotation.internalCommonAnnotationProcessor
name:org.springframework.context.event.internalEventListenerProcessor
name:org.springframework.context.event.internalEventListenerFactory
name:myConfig
name:org.springframework.aop.config.internalAutoProxyCreator

因此使用getBean去获取到这个类

AnnotationAwareAspectJAutoProxyCreator creator = (AnnotationAwareAspectJAutoProxyCreator) context.getBean("org.springframework.aop.config.internalAutoProxyCreator");

此时我们查看下AnnotationAwareAspectJAutoProxyCreator的类图继承关系

其中核心类是AbstractAutoProxyCreator、BeanPostProcessor

由于继承自BeanPostProcessor

public interface BeanPostProcessor {
	@Nullable
	default Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException {
		return bean;
	}
	@Nullable
	default Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException {
		return bean;
	}
}

看到AbstractAutoProxyCreator抽象类实现到的的两个核心方法

	@Override
	public Object postProcessBeforeInitialization(Object bean, String beanName) {
		return bean;
	}

	@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;
	}

因此，在AbstractAutoProxyCreator中，前置处理器是没有帮我们进行业务逻辑的处理，相关的业务逻辑处理，被其放在了后置处理器中进行处理。
由后置处理器判断，是否需要创造出一个代理对象
点进源码

	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);
			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;
	}

上述代码中

Object[] specificInterceptors = getAdvicesAndAdvisorsForBean(bean.getClass(), beanName, null);

这段作用是判断一下，你当前的这个bean是否需要做增强
然后

if (specificInterceptors != DO_NOT_PROXY) 

判断下如果为空，则不是切面类表示不需要增强，put一个key，value为false，作为一个标记位。

如果非空，则执行createProxy,创建一个代理类出来。

创建代理类源码如下

	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());
	}

前面一些判断，到最后

return proxyFactory.getProxy(getProxyClassLoader());

这个工厂点进去，点createAopProxy()这个方法进去

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

一直点到最后，最后就来到了我们aop的最最核心代码段

	@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);
		}
	}

显而易见一个判断

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

判断当前类，是否是接口的实现类，如果是，条件满足，则，走jdk动态代理
否则，走cglib代理模式