spring中的BeanDefinitionRegistryPostProcessor

spring中的BeanDefinitionRegistryPostProcessor是BeanFactoryPostProcessor的子接口，BeanFactoryPostProcessor的作用是在bean

的定义信息已经加载但还没有初始化的时候执行方法postProcessBeanFactory(）方法，而BeanDefinitionRegistryPostProcessor是在

BeanFactoryPostProcessor的前面执行。

public interface BeanDefinitionRegistryPostProcessor extends BeanFactoryPostProcessor {

    /**
     * Modify the application context's internal bean definition registry after its
     * standard initialization. All regular bean definitions will have been loaded,
     * but no beans will have been instantiated yet. This allows for adding further
     * bean definitions before the next post-processing phase kicks in.
     * @param registry the bean definition registry used by the application context
     * @throws org.springframework.beans.BeansException in case of errors
     */
    void postProcessBeanDefinitionRegistry(BeanDefinitionRegistry registry) throws BeansException;

}

自定义一个实现了BeanDefinitionRegistryPostProcessor接口的MyBeanDefinitionRegistryPostProcessor 实现类，它会重写

BeanDefinitionRegistryPostProcessor的postProcessBeanDefinitionRegistry（）方法和BeanFactoryPostProcessor的postProcessBeanFactory（）方法

@Component
public class MyBeanDefinitionRegistryPostProcessor implements BeanDefinitionRegistryPostProcessor {
    @Override
    public void postProcessBeanDefinitionRegistry(BeanDefinitionRegistry registry) throws BeansException {
　　　　　//BeanDefinitionRegistry可以给容器注册bean　
        System.out.println("MyBeanDefinitionRegistryPostProcessor...添加了foo之前的bean数="+registry.getBeanDefinitionCount());
        RootBeanDefinition rootBeanDefinition = new RootBeanDefinition(Foo.class);
        registry.registerBeanDefinition("helloFoo",rootBeanDefinition);
    }

    @Override
    public void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) throws BeansException {
        int beanDefinitionCount = beanFactory.getBeanDefinitionCount();
        System.out.println("MyBeanDefinitionRegistryPostProcessor...postProcessBeanFactory...的bean数="+beanDefinitionCount);
    }
}

配置类:

@Configuration
@Import({MyBeanDefinitionRegistryPostProcessor.class})
public class ExtConfig {

    @Bean
    public Foo foo(){
        return new Foo();
    }
}

foo类：

public class Foo {

    public Foo(){
        System.out.println("bean的创建");
    }


    @PostConstruct
    public void init(){
        System.out.println("bean的初始化");
    }

    @PreDestroy
    public void destroy(){
        System.out.println("bean的销毁");
    }
}

测试结果：

MyBeanDefinitionRegistryPostProcessor...添加了foo之前的bean数9
MyBeanDefinitionRegistryPostProcessor...postProcessBeanFactory...的bean数+10
bean的创建
bean的初始化
bean的创建
bean的初始化

debug:refresh()--》invokeBeanFactoryPostProcessors(),这里和注册bean和beanFactory类似，按照优先级的的来进行。

    // Do not initialize FactoryBeans here: We need to leave all regular beans
            // uninitialized to let the bean factory post-processors apply to them!
            // Separate between BeanDefinitionRegistryPostProcessors that implement
            // PriorityOrdered, Ordered, and the rest.
            List<BeanDefinitionRegistryPostProcessor> currentRegistryProcessors = new ArrayList<BeanDefinitionRegistryPostProcessor>();

            // First, invoke the BeanDefinitionRegistryPostProcessors that implement PriorityOrdered.
            String[] postProcessorNames =
                    beanFactory.getBeanNamesForType(BeanDefinitionRegistryPostProcessor.class, true, false);
            for (String ppName : postProcessorNames) {
                if (beanFactory.isTypeMatch(ppName, PriorityOrdered.class)) {
                    currentRegistryProcessors.add(beanFactory.getBean(ppName, BeanDefinitionRegistryPostProcessor.class));
                    processedBeans.add(ppName);
                }
            }
            sortPostProcessors(currentRegistryProcessors, beanFactory);
            registryProcessors.addAll(currentRegistryProcessors);
            invokeBeanDefinitionRegistryPostProcessors(currentRegistryProcessors, registry);
            currentRegistryProcessors.clear();

            // Next, invoke the BeanDefinitionRegistryPostProcessors that implement Ordered.
            postProcessorNames = beanFactory.getBeanNamesForType(BeanDefinitionRegistryPostProcessor.class, true, false);
            for (String ppName : postProcessorNames) {
                if (!processedBeans.contains(ppName) && beanFactory.isTypeMatch(ppName, Ordered.class)) {
                    currentRegistryProcessors.add(beanFactory.getBean(ppName, BeanDefinitionRegistryPostProcessor.class));
                    processedBeans.add(ppName);
                }
            }
            sortPostProcessors(currentRegistryProcessors, beanFactory);
            registryProcessors.addAll(currentRegistryProcessors);
            invokeBeanDefinitionRegistryPostProcessors(currentRegistryProcessors, registry);
            currentRegistryProcessors.clear();

            // Finally, invoke all other BeanDefinitionRegistryPostProcessors until no further ones appear.
            boolean reiterate = true;
            while (reiterate) {
                reiterate = false;
                postProcessorNames = beanFactory.getBeanNamesForType(BeanDefinitionRegistryPostProcessor.class, true, false);
                for (String ppName : postProcessorNames) {
                    if (!processedBeans.contains(ppName)) {
                        currentRegistryProcessors.add(beanFactory.getBean(ppName, BeanDefinitionRegistryPostProcessor.class));
                        processedBeans.add(ppName);
                        reiterate = true;
                    }
                }
                sortPostProcessors(currentRegistryProcessors, beanFactory);
                registryProcessors.addAll(currentRegistryProcessors);
                invokeBeanDefinitionRegistryPostProcessors(currentRegistryProcessors, registry);
                currentRegistryProcessors.clear();
            }

            // Now, invoke the postProcessBeanFactory callback of all processors handled so far.
            invokeBeanFactoryPostProcessors(registryProcessors, beanFactory);
            invokeBeanFactoryPostProcessors(regularPostProcessors, beanFactory);

invokeBeanDefinitionRegistryPostProcessors（）方法：

/**
     * Invoke the given BeanDefinitionRegistryPostProcessor beans.
     */
    private static void invokeBeanDefinitionRegistryPostProcessors(
            Collection<? extends BeanDefinitionRegistryPostProcessor> postProcessors, BeanDefinitionRegistry registry) {

        for (BeanDefinitionRegistryPostProcessor postProcessor : postProcessors) {
            postProcessor.postProcessBeanDefinitionRegistry(registry);
        }
    }

最后去执行invokeBeanFactoryPostProcessors（）方法；

/**
     * Invoke the given BeanFactoryPostProcessor beans.
     */
    private static void invokeBeanFactoryPostProcessors(
            Collection<? extends BeanFactoryPostProcessor> postProcessors, ConfigurableListableBeanFactory beanFactory) {

        for (BeanFactoryPostProcessor postProcessor : postProcessors) {
            postProcessor.postProcessBeanFactory(beanFactory);
        }
    }

它获取到所有的BeanFactoryPostProcessor 后，遍历执行每一个具体的方法：在这里会去调用

MyBeanDefinitionRegistryPostProcessor的postProcessBeanFactory（）方法：