Bean后置处理器 - BeanPostProcessor#postProcessAfterInitialization

Posted 2020-12-18 elvinle

spring在初始化之后, 还调用了一次 Bean 的后置处理器.

代码片段:

org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory#applyBeanPostProcessorsAfterInitialization

@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;
}

 同样的, 这里肯定也是6个后置处理器.

 

1.ApplicationContextAwareProcessor

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

这里啥也没干

 

2.ConfigurationClassPostProcessor$ImportAwareBeanPostProcessor

由父类实现:

org.springframework.beans.factory.config.InstantiationAwareBeanPostProcessorAdapter#postProcessAfterInitialization

@Override
public Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException {
    return bean;
}

 

3.PostProcessorRegistrationDelegate$BeanPostProcessorChecker

org.springframework.context.support.PostProcessorRegistrationDelegate.BeanPostProcessorChecker#postProcessAfterInitialization

@Override
public Object postProcessAfterInitialization(Object bean, String beanName) {
    if (!(bean instanceof BeanPostProcessor) && !isInfrastructureBean(beanName) &&
            this.beanFactory.getBeanPostProcessorCount() < this.beanPostProcessorTargetCount) {
        if (logger.isInfoEnabled()) {
            logger.info("Bean ‘" + beanName + "‘ of type [" + bean.getClass().getName() +
                    "] is not eligible for getting processed by all BeanPostProcessors " +
                    "(for example: not eligible for auto-proxying)");
        }
    }
    return bean;
}

private boolean isInfrastructureBean(@Nullable String beanName) {
    if (beanName != null && this.beanFactory.containsBeanDefinition(beanName)) {
        BeanDefinition bd = this.beanFactory.getBeanDefinition(beanName);
        return (bd.getRole() == RootBeanDefinition.ROLE_INFRASTRUCTURE);
    }
    return false;
}

从这里看, 并没有做实质性的操作, 主要是记录了日志.

主要是一个验证, 看看 执行过的后置处理器数量和目标数量, 是否相同.

其关键代码:

org.springframework.context.support.PostProcessorRegistrationDelegate#registerBeanPostProcessors

int beanProcessorTargetCount = beanFactory.getBeanPostProcessorCount() + 1 + postProcessorNames.length;
beanFactory.addBeanPostProcessor(new BeanPostProcessorChecker(beanFactory, beanProcessorTargetCount));

 

4.CommonAnnotationBeanPostProcessor

由其父类实现:

org.springframework.beans.factory.annotation.InitDestroyAnnotationBeanPostProcessor#postProcessAfterInitialization

@Override
public Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException {
    return bean;
}

里面啥也没干

 

5.AutowiredAnnotationBeanPostProcessor

由其父类实现:

org.springframework.beans.factory.config.InstantiationAwareBeanPostProcessorAdapter#postProcessAfterInitialization

@Override
public Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException {
    return bean;
}

 

6.ApplicationListenerDetector

@Override
public Object postProcessAfterInitialization(Object bean, String beanName) {
    if (bean instanceof ApplicationListener) {
        // potentially not detected as a listener by getBeanNamesForType retrieval
        Boolean flag = this.singletonNames.get(beanName);
        if (Boolean.TRUE.equals(flag)) {
            // singleton bean (top-level or inner): register on the fly
            this.applicationContext.addApplicationListener((ApplicationListener<?>) bean);
        }
        else if (Boolean.FALSE.equals(flag)) {
            if (logger.isWarnEnabled() && !this.applicationContext.containsBean(beanName)) {
                // inner bean with other scope - can‘t reliably process events
                logger.warn("Inner bean ‘" + beanName + "‘ implements ApplicationListener interface " +
                        "but is not reachable for event multicasting by its containing ApplicationContext " +
                        "because it does not have singleton scope. Only top-level listener beans are allowed " +
                        "to be of non-singleton scope.");
            }
            this.singletonNames.remove(beanName);
        }
    }
    return bean;
}

这里主要是将 实现了 ApplicationListener 接口的监听器, 加入到容器中.

如:

@Component
public class MyListener implements ApplicationListener<ApplicationEvent> {
    @Override
    public void onApplicationEvent(ApplicationEvent event) {
        System.out.println("MyListener : " + event);
    }
}

 

都说在这一步能产生 aop 代理, 那么从上面的代码, 暂时还没有看到. 接着前面的例子 getEarlyBeanReference 来看

示例

@Component
public class IndexA {

    @Autowired
    IndexB bbb;

    public IndexA() {
        System.out.println("IndexA constructor...");
    }

    public void printf(){
        System.out.println("indexA printf : ");
        System.out.println("indexB --> " + (bbb == null ? null : bbb.getClass().getName()));
    }
}

@Component
public class IndexB {

    @Autowired
    IndexA aaa;

    public IndexB() {
        System.out.println("IndexB constructor...");
    }

    public void printf(){
        System.out.println("indexB printf : ");
        System.out.println("indexA --> " + (aaa == null ? null : aaa.getClass().getName()));
    }
}

@Component
@Aspect
public class Aopa {

    @Pointcut("execution(* com.study.elvinle.ioc.cyc.IndexA.*(..))")
    public void pointCutMethodA() {
    }

    @Before("pointCutMethodA()")
    public void beforeA() {
        System.out.println("before invoke indexA.*() method -- Aopa");
    }

    @Pointcut("execution(* com.study.elvinle.ioc.cyc.IndexB.*(..))")
    public void pointCutMethodB() {
    }

    @Before("pointCutMethodB()")
    public void beforeB() {
        System.out.println("before invoke indexB.*() method -- Aopa");
    }
}

@EnableAspectJAutoProxy
@Configuration
@ComponentScan({
         "com.study.elvinle.ioc.cyc"
        , "com.study.elvinle.ioc.aop"
})
public class StartConfig {
}

测试代码:

public static void main(String[] args) {
    AnnotationConfigApplicationContext ac = new AnnotationConfigApplicationContext(StartConfig.class);
    IndexA a = ac.getBean(IndexA.class);
    System.out.println("spring‘s indexA --> " + a.getClass().getName());
    a.printf();
    System.out.println("======================");
    IndexB b = ac.getBean(IndexB.class);
    System.out.println("spring‘s indexB --> " + b.getClass().getName());
    b.printf();
}

调试结果:

 

 通过调试 applyBeanPostProcessorsAfterInitialization 方法看到, 此处多了一个后置处理器: 

AnnotationAwareAspectJAutoProxyCreator

 

AnnotationAwareAspectJAutoProxyCreator

方法藏的比较深, 由父类实现:

org.springframework.aop.framework.autoproxy.AbstractAutoProxyCreator#postProcessAfterInitialization

@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;
}

可以看到, 这里调用了前面同样的方法, 来产生代理:

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;
}

结合前面那篇和这篇来看, aop 代理的产生, 并不是全在 初始化方法之后的后置处理器中产生的. 

还有一部分是在 SmartInstantiationAwareBeanPostProcessor#getEarlyBeanReference 中产生的.

IndexA 在 getEarlyBeanReference 中产生代理之后, 在这里会再产生一次吗? 

答案是否定的. spring 很强大, 不会犯这种低级错误.