Spring AOP原理之@EnableAspectJAutoProxy

 

目錄

1. 說明

2. 原理

---

1. 說明

@EnableAspectJAutoProxy標記在主配置類上，表示開啓基於註解的aop模式；

2. 原理

• 2.1 @Import(AspectJAutoProxyRegistrar.class)， 給容器裏導入AspectJAutoProxyRegistrar；

@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Import(AspectJAutoProxyRegistrar.class) //通過@Import導入AspectJAutoProxyRegistrar
public @interface EnableAspectJAutoProxy {

	boolean proxyTargetClass() default false;

	boolean exposeProxy() default false;
}

•  2.2 AspectJAutoProxyRegistrar分析

AspectJAutoProxyRegistrar，實現org.springframework.context.annotation.ImportBeanDefinitionRegistrar接口，通過方法ImportBeanDefinitionRegistrar.registerBeanDefinitions向容器中導入組件的定義信息，具體的組件是org.springframework.aop.aspectj.annotation.AnnotationAwareAspectJAutoProxyCreator，name是“org.springframework.aop.config.internalAutoProxyCreator”；

class AspectJAutoProxyRegistrar implements ImportBeanDefinitionRegistrar {

	@Override
	public void registerBeanDefinitions(
			AnnotationMetadata importingClassMetadata, BeanDefinitionRegistry registry) {
		// 這裏會向容器中導入AnnotationAwareAspectJAutoProxyCreator
		AopConfigUtils.registerAspectJAnnotationAutoProxyCreatorIfNecessary(registry);

		AnnotationAttributes enableAspectJAutoProxy =
				AnnotationConfigUtils.attributesFor(importingClassMetadata, EnableAspectJAutoProxy.class);
		if (enableAspectJAutoProxy.getBoolean("proxyTargetClass")) {
			AopConfigUtils.forceAutoProxyCreatorToUseClassProxying(registry);
		}
		if (enableAspectJAutoProxy.getBoolean("exposeProxy")) {
			AopConfigUtils.forceAutoProxyCreatorToExposeProxy(registry);
		}
	}
}

在org.springframework.aop.config.AopConfigUtils中，代碼如下：

public static BeanDefinition registerAspectJAnnotationAutoProxyCreatorIfNecessary(BeanDefinitionRegistry registry) {
	return registerAspectJAnnotationAutoProxyCreatorIfNecessary(registry, null);
}

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

public static final String AUTO_PROXY_CREATOR_BEAN_NAME ="org.springframework.aop.config.internalAutoProxyCreator";

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;
	}
	// 創建組件的定義信息
	RootBeanDefinition beanDefinition = new RootBeanDefinition(cls);
	beanDefinition.setSource(source);
	beanDefinition.getPropertyValues().add("order", Ordered.HIGHEST_PRECEDENCE);
	beanDefinition.setRole(BeanDefinition.ROLE_INFRASTRUCTURE);
	// 註冊到容器中
	registry.registerBeanDefinition(AUTO_PROXY_CREATOR_BEAN_NAME, beanDefinition);
	return beanDefinition;
}