BeanFactoryPostProcessor & BeanDefinitionRegistryPostProcessor——执行时机

BeanDefinitionRegistryPostProcessor继承自BeanFactoryPostProcessor。

BeanFactoryPostProcessor

@FunctionalInterface
public interface BeanFactoryPostProcessor {
	void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) throws BeansException;
}

BeanDefinitionRegistryPostProcessor

public interface BeanDefinitionRegistryPostProcessor extends BeanFactoryPostProcessor {
	void postProcessBeanDefinitionRegistry(BeanDefinitionRegistry registry) throws BeansException;
}

执行时机：抽象的来看就是 BeanFactory加载完Bean定义后，实例化Bean之前执行。
从代码角度就是AbstractApplicationContext#refresh中的invokeBeanFactoryPostProcessors(beanFactory);语句（以下代码的第22行）

	public void refresh() throws BeansException, IllegalStateException {
		synchronized (this.startupShutdownMonitor) {
			StartupStep contextRefresh = this.applicationStartup.start("spring.context.refresh");

			// Prepare this context for refreshing.
			prepareRefresh();

			// Tell the subclass to refresh the internal bean factory.
			ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();

			// Prepare the bean factory for use in this context.
			prepareBeanFactory(beanFactory);

			try {
				// Allows post-processing of the bean factory in context subclasses.
				postProcessBeanFactory(beanFactory);

				StartupStep beanPostProcess = this.applicationStartup.start("spring.context.beans.post-process");

				// 执行时机
				// Invoke factory processors registered as beans in the context.
				invokeBeanFactoryPostProcessors(beanFactory);

				// Register bean processors that intercept bean creation.
				registerBeanPostProcessors(beanFactory);
				beanPostProcess.end();

				// Initialize message source for this context.
				initMessageSource();

				// Initialize event multicaster for this context.
				initApplicationEventMulticaster();

				// Initialize other special beans in specific context subclasses.
				onRefresh();

				// Check for listener beans and register them.
				registerListeners();

				// Instantiate all remaining (non-lazy-init) singletons.
				finishBeanFactoryInitialization(beanFactory);

				// Last step: publish corresponding event.
				finishRefresh();
			} catch // ...
			  finally // ...
		}
	}

invokeBeanFactoryPostProcessors

	protected void invokeBeanFactoryPostProcessors(ConfigurableListableBeanFactory beanFactory) {
		PostProcessorRegistrationDelegate.invokeBeanFactoryPostProcessors(beanFactory, getBeanFactoryPostProcessors());
		// ...
	}

PostProcessorRegistrationDelegate#invokeBeanFactoryPostProcessors

	public static void invokeBeanFactoryPostProcessors(ConfigurableListableBeanFactory beanFactory, List<BeanFactoryPostProcessor> beanFactoryPostProcessors) {
		// 流程过于复杂，就全部省略了
		if (beanFactory instanceof BeanDefinitionRegistry) {
			// ...
			boolean reiterate = true;
			while (reiterate) {
				// ... BeanDefinitionRegistryPostProcessor
				invokeBeanDefinitionRegistryPostProcessors(currentRegistryProcessors, registry, beanFactory.getApplicationStartup());
				currentRegistryProcessors.clear();
			}
			// Now, invoke the postProcessBeanFactory callback of all processors handled so far.
			invokeBeanFactoryPostProcessors(registryProcessors, beanFactory);
			invokeBeanFactoryPostProcessors(regularPostProcessors, beanFactory);
		} else {
			// Invoke factory processors registered with the context instance.
			invokeBeanFactoryPostProcessors(beanFactoryPostProcessors, beanFactory);
		}
		// 排序 按顺序执行 
		// implement PriorityOrdered ...
		invokeBeanFactoryPostProcessors(priorityOrderedPostProcessors, beanFactory);
		// implement Ordered ...
		invokeBeanFactoryPostProcessors(orderedPostProcessors, beanFactory);
		// all other BeanFactoryPostProcessors ...
		invokeBeanFactoryPostProcessors(nonOrderedPostProcessors, beanFactory);
		
		beanFactory.clearMetadataCache();	
	}

invokeBeanFactoryPostProcessors——调用BeanFactoryPostProcessor接口

	private static void invokeBeanFactoryPostProcessors(Collection<? extends BeanFactoryPostProcessor> postProcessors, ConfigurableListableBeanFactory beanFactory) {
		for (BeanFactoryPostProcessor postProcessor : postProcessors) {
			StartupStep postProcessBeanFactory = beanFactory.getApplicationStartup().start("spring.context.bean-factory.post-process").tag("postProcessor", postProcessor::toString);
			
			// 在此处调用 BeanFactoryPostProcessor 
			postProcessor.postProcessBeanFactory(beanFactory);
			postProcessBeanFactory.end();
		}
	}

invokeBeanDefinitionRegistryPostProcessors——调用BeanDefinitionRegistryPostProcessor接口

	private static void invokeBeanDefinitionRegistryPostProcessors(Collection<? extends BeanDefinitionRegistryPostProcessor> postProcessors, BeanDefinitionRegistry registry, ApplicationStartup applicationStartup) {
		for (BeanDefinitionRegistryPostProcessor postProcessor : postProcessors) {
			StartupStep postProcessBeanDefRegistry = applicationStartup.start("spring.context.beandef-registry.post-process").tag("postProcessor", postProcessor::toString);
			
			// 在此处调用 BeanDefinitionRegistryPostProcessor
			postProcessor.postProcessBeanDefinitionRegistry(registry);
			postProcessBeanDefRegistry.end();
		}
	}

所以可以看出先调用BeanDefinitionRegistryPostProcessor，后调用BeanFactoryPostProcessor，而BeanDefinitionRegistryPostProcessor继承自BeanFactoryPostProcessor。

---

所以抽象的来看，执行时机是在 BeanFactory加载完Bean定义后，实例化Bean之前。且先执行BeanDefinitionRegistryPostProcessor的postProcessBeanDefinitionRegistry方法，再执行BeanFactoryPostProcessor的postProcessBeanFactory方法。
如果在postProcessBeanDefinitionRegistry方法中增加一个bean定义，那么在postProcessBeanFactory方法中是可以拿到的。