Spring IoC源码学习：registerBeanPostProcessors 详解

protected void registerBeanPostProcessors(ConfigurableListableBeanFactory beanFactory) {
    // 1.注册BeanPostProcessor
    PostProcessorRegistrationDelegate.registerBeanPostProcessors(beanFactory, this);
}

public static void registerBeanPostProcessors(
        ConfigurableListableBeanFactory beanFactory, AbstractApplicationContext applicationContext) {
    // 1.找出所有实现BeanPostProcessor接口的类
    String[] postProcessorNames = beanFactory.getBeanNamesForType(BeanPostProcessor.class, true, false);
    // Register BeanPostProcessorChecker that logs an info message when
    // a bean is created during BeanPostProcessor instantiation, i.e. when
    // a bean is not eligible for getting processed by all BeanPostProcessors.
    // BeanPostProcessor的目标计数
    int beanProcessorTargetCount = beanFactory.getBeanPostProcessorCount() + 1 + postProcessorNames.length;
    // 2.添加BeanPostProcessorChecker(主要用于记录信息)到beanFactory中
    beanFactory.addBeanPostProcessor(new BeanPostProcessorChecker(beanFactory, beanProcessorTargetCount));
    // Separate between BeanPostProcessors that implement PriorityOrdered,
    // Ordered, and the rest.
    // 3.定义不同的变量用于区分: 实现PriorityOrdered接口的BeanPostProcessor、实现Ordered接口的BeanPostProcessor、普通BeanPostProcessor
    // 3.1 priorityOrderedPostProcessors: 用于存放实现PriorityOrdered接口的BeanPostProcessor
    List<BeanPostProcessor> priorityOrderedPostProcessors = new ArrayList<BeanPostProcessor>();
    // 3.2 internalPostProcessors: 用于存放Spring内部的BeanPostProcessor
    List<BeanPostProcessor> internalPostProcessors = new ArrayList<BeanPostProcessor>();
    // 3.3 orderedPostProcessorNames: 用于存放实现Ordered接口的BeanPostProcessor的beanName
    List<String> orderedPostProcessorNames = new ArrayList<String>();
    // 3.4 nonOrderedPostProcessorNames: 用于存放普通BeanPostProcessor的beanName
    List<String> nonOrderedPostProcessorNames = new ArrayList<String>();
    // 4.遍历postProcessorNames, 将BeanPostProcessors按3.1 - 3.4定义的变量区分开
    for (String ppName : postProcessorNames) {
        if (beanFactory.isTypeMatch(ppName, PriorityOrdered.class)) {
            // 4.1 如果ppName对应的Bean实例实现了PriorityOrdered接口, 则拿到ppName对应的Bean实例并添加到priorityOrderedPostProcessors
            BeanPostProcessor pp = beanFactory.getBean(ppName, BeanPostProcessor.class);
            priorityOrderedPostProcessors.add(pp);
            if (pp instanceof MergedBeanDefinitionPostProcessor) {
                // 4.2 如果ppName对应的Bean实例也实现了MergedBeanDefinitionPostProcessor接口,
                // 则将ppName对应的Bean实例添加到internalPostProcessors
                internalPostProcessors.add(pp);
            }
        }
        else if (beanFactory.isTypeMatch(ppName, Ordered.class)) {
            // 4.3 如果ppName对应的Bean实例没有实现PriorityOrdered接口, 但是实现了Ordered接口, 则将ppName添加到orderedPostProcessorNames
            orderedPostProcessorNames.add(ppName);
        }
        else {
            // 4.4 否则, 将ppName添加到nonOrderedPostProcessorNames
            nonOrderedPostProcessorNames.add(ppName);
        }
    }
    // First, register the BeanPostProcessors that implement PriorityOrdered.
    // 5.首先, 注册实现PriorityOrdered接口的BeanPostProcessors
    // 5.1 对priorityOrderedPostProcessors进行排序
    sortPostProcessors(priorityOrderedPostProcessors, beanFactory);
    // 5.2 注册priorityOrderedPostProcessors
    registerBeanPostProcessors(beanFactory, priorityOrderedPostProcessors);
    // Next, register the BeanPostProcessors that implement Ordered.
    // 6.接下来, 注册实现Ordered接口的BeanPostProcessors
    List<BeanPostProcessor> orderedPostProcessors = new ArrayList<BeanPostProcessor>();
    for (String ppName : orderedPostProcessorNames) {
        // 6.1 拿到ppName对应的BeanPostProcessor实例对象
        BeanPostProcessor pp = beanFactory.getBean(ppName, BeanPostProcessor.class);
        // 6.2 将ppName对应的BeanPostProcessor实例对象添加到orderedPostProcessors, 准备执行注册
        orderedPostProcessors.add(pp);
        if (pp instanceof MergedBeanDefinitionPostProcessor) {
            // 6.3 如果ppName对应的Bean实例也实现了MergedBeanDefinitionPostProcessor接口,
            // 则将ppName对应的Bean实例添加到internalPostProcessors
            internalPostProcessors.add(pp);
        }
    }
    // 6.4 对orderedPostProcessors进行排序
    sortPostProcessors(orderedPostProcessors, beanFactory);
    // 6.5 注册orderedPostProcessors
    registerBeanPostProcessors(beanFactory, orderedPostProcessors);
    // Now, register all regular BeanPostProcessors.
    // 7.注册所有常规的BeanPostProcessors（过程与6类似）
    List<BeanPostProcessor> nonOrderedPostProcessors = new ArrayList<BeanPostProcessor>();
    for (String ppName : nonOrderedPostProcessorNames) {
        BeanPostProcessor pp = beanFactory.getBean(ppName, BeanPostProcessor.class);
        nonOrderedPostProcessors.add(pp);
        if (pp instanceof MergedBeanDefinitionPostProcessor) {
            internalPostProcessors.add(pp);
        }
    }
    registerBeanPostProcessors(beanFactory, nonOrderedPostProcessors);
    // Finally, re-register all internal BeanPostProcessors.
    // 8.最后, 重新注册所有内部BeanPostProcessors（相当于内部的BeanPostProcessor会被移到处理器链的末尾）
    // 8.1 对internalPostProcessors进行排序
    sortPostProcessors(internalPostProcessors, beanFactory);
    // 8.2注册internalPostProcessors
    registerBeanPostProcessors(beanFactory, internalPostProcessors);
    // Re-register post-processor for detecting inner beans as ApplicationListeners,
    // moving it to the end of the processor chain (for picking up proxies etc).
    // 9.重新注册ApplicationListenerDetector（跟8类似，主要是为了移动到处理器链的末尾）
    beanFactory.addBeanPostProcessor(new ApplicationListenerDetector(applicationContext));
}

private static void registerBeanPostProcessors(
        ConfigurableListableBeanFactory beanFactory, List<BeanPostProcessor> postProcessors) {
    // 1.遍历postProcessors
    for (BeanPostProcessor postProcessor : postProcessors) {
        // 2.将PostProcessor添加到BeanFactory中的beanPostProcessors缓存
        beanFactory.addBeanPostProcessor(postProcessor);
    }
}

@Override
public void addBeanPostProcessor(BeanPostProcessor beanPostProcessor) {
    Assert.notNull(beanPostProcessor, "BeanPostProcessor must not be null");
    // 1.如果beanPostProcessor已经存在则移除（可以起到排序的效果，beanPostProcessor可能本来在前面，移除再添加，则变到最后面）
    this.beanPostProcessors.remove(beanPostProcessor);
    // 2.将beanPostProcessor添加到beanPostProcessors缓存
    this.beanPostProcessors.add(beanPostProcessor);
    if (beanPostProcessor instanceof InstantiationAwareBeanPostProcessor) {
        // 3.如果beanPostProcessor是InstantiationAwareBeanPostProcessor, 则将hasInstantiationAwareBeanPostProcessors设置为true,
        // 该变量用于指示beanFactory是否已注册过InstantiationAwareBeanPostProcessors
        this.hasInstantiationAwareBeanPostProcessors = true;
    }
    if (beanPostProcessor instanceof DestructionAwareBeanPostProcessor) {
        // 4.如果beanPostProcessor是DestructionAwareBeanPostProcessor, 则将hasInstantiationAwareBeanPostProcessors设置为true,
        // 该变量用于指示beanFactory是否已注册过DestructionAwareBeanPostProcessor
        this.hasDestructionAwareBeanPostProcessors = true;
    }
}

package com.joonwhee.open.demo.spring;
import com.joonwhee.open.demo.service.UserService;
import org.springframework.beans.BeansException;
import org.springframework.beans.factory.config.BeanPostProcessor;
import org.springframework.core.PriorityOrdered;
/**
 * @author joonwhee
 * @date 2019/2/23
 */
@Component
public class MyBeanPostProcessor implements BeanPostProcessor, PriorityOrdered {
    @Override
    public Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException {
        System.out.println("MyBeanPostProcessor#postProcessBeforeInitialization");
        if (bean instanceof UserService) {
            System.out.println(beanName);
        }
        // 自己的逻辑
        return bean;
    }
    @Override
    public Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException {
        System.out.println("MyBeanPostProcessor#postProcessAfterInitialization");
        // 自己的逻辑
        return bean;
    }
    @Override
    public int getOrder() {
        return 0;
    }
}