使用

spring4.0之后能夠很方便的使用spring aop，使用@EnableAspectJAutoProxy開啟aop锦亦，使用@Aspect注解聲明切面舶替。

@Configuration
@ComponentScan
@EnableAspectJAutoProxy
public class PerformConfig {
}

public interface Performance {

    void perform();
}

@Component
public class PerformanceImpl implements  Performance{
    @Override
    public void perform() {
        System.out.println("perform");
    }
}

@Aspect
@Component
public class Audience {

    @Pointcut("execution(* com.ming.aop.Performance.*(..))")
    public void perform(){
    }

    @Before("perform()")
    public void takeSeats() {
        System.out.println("perform before take seats");
    }

    @AfterReturning("perform()")
    public void applause() {
        System.out.println("CLAP CLAP CLAP");
    }

    @AfterThrowing("perform()")
    public void demandRefund() {
        System.out.println("demanding a refund");
    }
}

原理解析

@EnableAspectJAutoProxy注解是開啟spring aop，@EnableAspectJAutoProxy注解源碼如下:

@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Import(AspectJAutoProxyRegistrar.class)
public @interface EnableAspectJAutoProxy {
    boolean proxyTargetClass() default false;

    boolean exposeProxy() default false;
}

通過@Import注解導(dǎo)入bean杠园，在八顾瞪、spring ioc之@Import解析中講了@Import三種導(dǎo)入方式，@EnableAspectJAutoProxy是屬于動態(tài)注冊Bean抛蚁，會調(diào)用AspectJAutoProxyRegistrar類的registerBeanDefinitions陈醒，registerBeanDefinitions實現(xiàn)邏輯如下:

@Override
public void registerBeanDefinitions(
        AnnotationMetadata importingClassMetadata, BeanDefinitionRegistry registry) {
    //注冊AnnotationAwareAspectJAutoProxyCreator bean
    AopConfigUtils.registerAspectJAnnotationAutoProxyCreatorIfNecessary(registry);

    //根據(jù)注解設(shè)置屬性值
    AnnotationAttributes enableAspectJAutoProxy =
            AnnotationConfigUtils.attributesFor(importingClassMetadata, EnableAspectJAutoProxy.class);
    if (enableAspectJAutoProxy.getBoolean("proxyTargetClass")) {
        AopConfigUtils.forceAutoProxyCreatorToUseClassProxying(registry);
    }
    if (enableAspectJAutoProxy.getBoolean("exposeProxy")) {
        AopConfigUtils.forceAutoProxyCreatorToExposeProxy(registry);
    }
}

AopConfigUtils.registerAspectJAnnotationAutoProxyCreatorIfNecessary(registry)調(diào)用鏈比較多，但是主要目的是注冊AnnotationAwareAspectJAutoProxyCreator bean篮绿，注冊這個bean有什么用呢孵延？

AnnotationAwareAspectJAutoProxyCreator類圖

AnnotationAwareAspectJAutoProxyCreator類圖

AnnotationAwareAspectJAutoProxyCreator驅(qū)動器實現(xiàn)邏輯

AnnotationAwareAspectJAutoProxyCreator驅(qū)動器的實現(xiàn)邏輯主要在父類AbstractAutoProxyCreator中犬钢。

@Override
public Object postProcessBeforeInitialization(Object bean, String beanName) {
    //前置驅(qū)動直接返回bean
    return bean;
}
@Override
public Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException {
    if (bean != null) {
        Object cacheKey = getCacheKey(bean.getClass(), beanName);
        if (!this.earlyProxyReferences.contains(cacheKey)) {
            //后置驅(qū)動器把邏輯交給了wrapIfNecessary方法
            return wrapIfNecessary(bean, beanName, cacheKey);
        }
    }
    return bean;
}

protected Object wrapIfNecessary(Object bean, String beanName, Object cacheKey) {
    if (beanName != null && 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.
    //如果存在適合當(dāng)前bean的增強方法，則創(chuàng)建代理
    Object[] specificInterceptors = getAdvicesAndAdvisorsForBean(bean.getClass(), beanName, null);
    if (specificInterceptors != DO_NOT_PROXY) {
        this.advisedBeans.put(cacheKey, Boolean.TRUE);
        //創(chuàng)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;
}

前置驅(qū)動器直接返回bean思灰，后置驅(qū)動把邏輯交給了wrapIfNecessary方法玷犹，wrapIfNecessary主要的邏輯是查找是否存在匹配當(dāng)前bean的增加方法，如果存在則創(chuàng)建bean洒疚。所以接下來主要分析：

1. 如何查找匹配的增強器
2. 如何創(chuàng)建代理