Java 图解Spring启动时的后置处理器工作流程是怎样的

AnnotationConfigApplicationContext applicationContext = new AnnotationConfigApplicationContext();
// ......
applicationContext.refresh();

public void refresh() throws BeansException, IllegalStateException {
		synchronized (this.startupShutdownMonitor) {
			// Prepare this context for refreshing.
			// 启动前的准备工作：记录启动时间，活动标记为启动以及环境属性变量集合的初始化
			prepareRefresh();
			// Tell the subclass to refresh the internal bean factory.
			ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();
			// Prepare the bean factory for use in this context.
			//还是一些准备工作，添加了两个后置处理器：ApplicationContextAwareProcessor，ApplicationListenerDetector
			//还设置了 忽略自动装配 和 允许自动装配 的接口
			//对环境，系统环境，系统属性三个Bean如果不存在某个bean的时候，spring就自动生成singleton bean（Not bd）
			//还设置了bean表达式解析器 等
			prepareBeanFactory(beanFactory);
			try {
				// Allows post-processing of the bean factory in context subclasses.
				// 空方法
				postProcessBeanFactory(beanFactory);
				// Invoke factory processors registered as beans in the context.
				//执行自定义的BeanFactoryProcessor和内置的BeanFactoryProcessor
				invokeBeanFactoryPostProcessors(beanFactory);
				// Register bean processors that intercept bean creation.
				registerBeanPostProcessors(beanFactory);
				// 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();
			}
			finally {
				// Reset common introspection caches in Spring's core, since we
				// might not ever need metadata for singleton beans anymore...
				resetCommonCaches();
			}
		}
	}

	protected void prepareRefresh() {
		// Switch to active.
		this.startupDate = System.currentTimeMillis();
		this.closed.set(false);
		this.active.set(true);
		// Initialize any placeholder property sources in the context environment.
		// 空方法
		initPropertySources();
		// Validate that all properties marked as required are resolvable:
		// see ConfigurablePropertyResolver#setRequiredProperties
		getEnvironment().validateRequiredProperties();
		// Store pre-refresh ApplicationListeners...
		if (this.earlyApplicationListeners == null) {
			this.earlyApplicationListeners = new LinkedHashSet<>(this.applicationListeners);
		}
		else {
			// Reset local application listeners to pre-refresh state.
			this.applicationListeners.clear();
			this.applicationListeners.addAll(this.earlyApplicationListeners);
		}
		// Allow for the collection of early ApplicationEvents,
		// to be published once the multicaster is available...
		this.earlyApplicationEvents = new LinkedHashSet<>();
	}

protected ConfigurableListableBeanFactory obtainFreshBeanFactory() {
		// CAS保证同步
		refreshBeanFactory();
		// 返回beanFactory- DefaultListableBeanFactory.class
		ConfigurableListableBeanFactory beanFactory = getBeanFactory();
		return beanFactory;
	}

protected void prepareBeanFactory(ConfigurableListableBeanFactory beanFactory)  {
    	// Tell the internal bean factory to use the context's class loader etc.
		beanFactory.setBeanClassLoader(getClassLoader());
		//设置bean表达式解析器
		beanFactory.setBeanExpressionResolver(new StandardBeanExpressionResolver(beanFactory.getBeanClassLoader()));
		//属性编辑器支持
		beanFactory.addPropertyEditorRegistrar(new ResourceEditorRegistrar(this, getEnvironment()));

		// Configure the bean factory with context callbacks.
		//添加一个后置处理器：ApplicationContextAwareProcessor，此后置处理处理器实现了BeanPostProcessor接口
		beanFactory.addBeanPostProcessor(new ApplicationContextAwareProcessor(this));
		//以下接口，忽略自动装配
		beanFactory.ignoreDependencyInterface(EnvironmentAware.class);
   		// .....
    	// BeanFactory interface not registered as resolvable type in a plain factory.
		// MessageSource registered (and found for autowiring) as a bean.
		//以下接口，允许自动装配,第一个参数是自动装配的类型，，第二个字段是自动装配的值
		// 这个接口仅会将注入的参数XXX.class注入为指定的值，但不影响XXX.class创建Bean对象；
		beanFactory.registerResolvableDependency(BeanFactory.class, beanFactory);
		beanFactory.registerResolvableDependency(ResourceLoader.class, this);
    	// Register default environment beans.
		// 环境，系统环境，系统属性 因此通常情况下，这三个Bean是没有bd的
		//如果没有注册过bean名称为XXX，spring就自己创建一个名称为XXX的singleton bean
		if (!beanFactory.containsLocalBean(ENVIRONMENT_BEAN_NAME)) {
			beanFactory.registerSingleton(ENVIRONMENT_BEAN_NAME, getEnvironment());
		}
		if (!beanFactory.containsLocalBean(SYSTEM_PROPERTIES_BEAN_NAME)) {
			beanFactory.registerSingleton(SYSTEM_PROPERTIES_BEAN_NAME, getEnvironment().getSystemProperties());
		}
		if (!beanFactory.containsLocalBean(SYSTEM_ENVIRONMENT_BEAN_NAME)) {
			beanFactory.registerSingleton(SYSTEM_ENVIRONMENT_BEAN_NAME, getEnvironment().getSystemEnvironment());
		}
}

protected void invokeBeanFactoryPostProcessors(ConfigurableListableBeanFactory beanFactory) {
	// getBeanFactoryPostProcessors是spring允许我们手动添加BeanFactoryPostProcessor
	// 即：annotationConfigApplicationContext.addBeanFactoryPostProcessor(XXX);
    // 未手动添加的话，getBeanFactoryPostProcessors()为empty
		PostProcessorRegistrationDelegate.invokeBeanFactoryPostProcessors(beanFactory, getBeanFactoryPostProcessors());

		// Detect a LoadTimeWeaver and prepare for weaving, if found in the meantime
		// (e.g. through an @Bean method registered by ConfigurationClassPostProcessor)
		if (beanFactory.getTempClassLoader() == null && beanFactory.containsBean(LOAD_TIME_WEAVER_BEAN_NAME)) {
			beanFactory.addBeanPostProcessor(new LoadTimeWeaverAwareProcessor(beanFactory));
			beanFactory.setTempClassLoader(new ContextTypeMatchClassLoader(beanFactory.getBeanClassLoader()));
		}
	}

public class ConfigurationClassPostProcessor implements BeanDefinitionRegistryPostProcessor,
		PriorityOrdered, ResourceLoaderAware, BeanClassLoaderAware, EnvironmentAware {}

public static void invokeBeanFactoryPostProcessors(
			ConfigurableListableBeanFactory beanFactory, List<BeanFactoryPostProcessor> beanFactoryPostProcessors) {

		// Invoke BeanDefinitionRegistryPostProcessors first, if any.
		Set<String> processedBeans = new HashSet<>();

		// 如果不是BeanDefinitionRegistry 则直接执行beanFactoryPostProcessors
		// 刚启动时传入的beanFactory是DefaultListableBeanFactory，他是实现了BeanDefinitionRegistry 因此会走这里
		if (beanFactory instanceof BeanDefinitionRegistry) {
			BeanDefinitionRegistry registry = (BeanDefinitionRegistry) beanFactory;
			// bf后置处理器集合（手动添加与bdr后置处理器集合【下面的那个集合】）：因为bdrp属于bfp
			List<BeanFactoryPostProcessor> regularPostProcessors = new ArrayList<>();
			// bdr后置处理器集合（手动添加与spring自己的）
			List<BeanDefinitionRegistryPostProcessor> registryProcessors = new ArrayList<>();

			// 循环传进来的beanFactoryPostProcessors，刚启动时未手动增加的情况下beanFactoryPostProcessors肯定没有数据
			// 因为beanFactoryPostProcessors是获得手动添加的，而不是spring扫描的
			// 只有手动调用annotationConfigApplicationContext.addBeanFactoryPostProcessor(XXX)才会有数据
			// 执行手动添加的beanFactoryPostProcessors， 如果是BeanDefinitionRegistryPostProcessor，则执行其postProcessBeanDefinitionRegistry再加到list中
			for (BeanFactoryPostProcessor postProcessor : beanFactoryPostProcessors) {
				if (postProcessor instanceof BeanDefinitionRegistryPostProcessor) {
					BeanDefinitionRegistryPostProcessor registryProcessor =
							(BeanDefinitionRegistryPostProcessor) postProcessor;
					registryProcessor.postProcessBeanDefinitionRegistry(registry);
					registryProcessors.add(registryProcessor);
				}
				else {
					regularPostProcessors.add(postProcessor);
				}
			}
			//一个临时变量，用来装载BeanDefinitionRegistryPostProcessor为了排序
			//BeanDefinitionRegistry继承了PostProcessorBeanFactoryPostProcessor
			List<BeanDefinitionRegistryPostProcessor> currentRegistryProcessors = new ArrayList<>();

			// 获得实现BeanDefinitionRegistryPostProcessor接口的类
			// 就是ConfigurationClassPostProcessor（Spring自己添加的-在reader()时增加的）
			String[] postProcessorNames =
					beanFactory.getBeanNamesForType(BeanDefinitionRegistryPostProcessor.class, true, false);
			for (String ppName : postProcessorNames) {
				if (beanFactory.isTypeMatch(ppName, PriorityOrdered.class)) {
					//获得ConfigurationClassPostProcessor类，并且放到currentRegistryProcessors
					//ConfigurationClassPostProcessor是很重要的一个类，它实现了BeanDefinitionRegistryPostProcessor接口
					//BeanDefinitionRegistryPostProcessor接口又实现了BeanFactoryPostProcessor接口
					//ConfigurationClassPostProcessor是极其重要的类
					//里面执行了扫描Bean，Import，ImportResouce等各种操作
					//用来处理配置类（有两种情况 一种是传统意义上的配置类，一种是普通的bean）的各种逻辑
					currentRegistryProcessors.add(beanFactory.getBean(ppName, BeanDefinitionRegistryPostProcessor.class));
					//把name放到processedBeans，后续会根据这个集合来判断处理器是否已经被执行过了
					processedBeans.add(ppName);
				}
			}
			//处理排序
			sortPostProcessors(currentRegistryProcessors, beanFactory);
			//合并Processors，为什么要合并，因为registryProcessors是装载BeanDefinitionRegistryPostProcessor的
			//一开始的时候，spring只会执行BeanDefinitionRegistryPostProcessor独有的方法
			//而不会执行BeanDefinitionRegistryPostProcessor父类的方法，即BeanFactoryProcessor的方法
			//所以这里需要把处理器放入一个集合中，后续统一执行父类的方法
			registryProcessors.addAll(currentRegistryProcessors);
			//可以理解为执行ConfigurationClassPostProcessor的postProcessBeanDefinitionRegistry方法
			//Spring热插播的体现，像ConfigurationClassPostProcessor就相当于一个组件，Spring很多事情就是交给组件去管理
			//将spring提供的RegistryProcessors(就是这个ConfigurationClassPostProcessor)执行其postProcessBeanDefinitionRegistry
			invokeBeanDefinitionRegistryPostProcessors(currentRegistryProcessors, registry);
			//清空临时变量
			currentRegistryProcessors.clear();
			// 再次根据BeanDefinitionRegistryPostProcessor获得BeanName，看这个BeanName是否已经被执行过了，有没有实现Ordered接口
			// 如果没有被执行过，也实现了Ordered接口的话，把对象推送到currentRegistryProcessors，名称推送到processedBeans
			// 如果没有实现Ordered接口的话，这里不把数据加到currentRegistryProcessors，processedBeans中，后续再做处理
			// 这里才可以获得我们定义的实现了BeanDefinitionRegistryPostProcessor的Bean
			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);
				}
			}
			//处理排序
			sortPostProcessors(currentRegistryProcessors, beanFactory);
			//合并Processors
			registryProcessors.addAll(currentRegistryProcessors);
			//执行有Ordered的BeanDefinitionRegistryPostProcessor
			invokeBeanDefinitionRegistryPostProcessors(currentRegistryProcessors, registry);
			//清空临时变量
			currentRegistryProcessors.clear();

			// Finally, invoke all other BeanDefinitionRegistryPostProcessors until no further ones appear.
			// 下面的代码就是执行没有实现PriorityOrdered接口也没有Ordered的BeanDefinitionRegistryPostProcessor
			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.
			//registryProcessors集合装载BeanDefinitionRegistryPostProcessor
			//上面的代码是执行bfr后置处理器子类独有的方法，这里需要再把bfr后置处理器父类的方法也执行一次
			invokeBeanFactoryPostProcessors(registryProcessors, beanFactory);
			//regularPostProcessors装载BeanFactoryPostProcessor，执行BeanFactoryPostProcessor的方法
			//但是regularPostProcessors一般情况下，是不会有数据的，只有在外面手动添加BeanFactoryPostProcessor，才会有数据
			invokeBeanFactoryPostProcessors(regularPostProcessors, beanFactory);
		}

		else {
			// Invoke factory processors registered with the context instance.
			// 若bfp没有继承bdrp则直接执行手动增加bf后置处理器的后置处理器
			invokeBeanFactoryPostProcessors(beanFactoryPostProcessors, beanFactory);
		}

		// Do not initialize FactoryBeans here: We need to leave all regular beans
		// uninitialized to let the bean factory post-processors apply to them!
		// 找到BeanFactoryPostProcessor实现类的BeanName数组
		// 处理Spring自己的bf后置处理器
		String[] postProcessorNames =
				beanFactory.getBeanNamesForType(BeanFactoryPostProcessor.class, true, false);

		// Separate between BeanFactoryPostProcessors that implement PriorityOrdered,
		// Ordered, and the rest.
		// PriorityOrdered的bf后置处理器集合
		List<BeanFactoryPostProcessor> priorityOrderedPostProcessors = new ArrayList<>();
		// Ordered的bf后置处理器集合
		List<String> orderedPostProcessorNames = new ArrayList<>();
		// 无PriorityOrdered无Ordered的bf后置处理器集合
		List<String> nonOrderedPostProcessorNames = new ArrayList<>();
		//循环BeanName数组
		for (String ppName : postProcessorNames) {
			//如果这个Bean被执行过了，跳过
			if (processedBeans.contains(ppName)) {
				// skip - already processed in first phase above
			}
			//如果实现了PriorityOrdered接口，加入到priorityOrderedPostProcessors
			else if (beanFactory.isTypeMatch(ppName, PriorityOrdered.class)) {
				priorityOrderedPostProcessors.add(beanFactory.getBean(ppName, BeanFactoryPostProcessor.class));
			}
			//如果实现了Ordered接口，加入到orderedPostProcessorNames
			else if (beanFactory.isTypeMatch(ppName, Ordered.class)) {
				orderedPostProcessorNames.add(ppName);
			}
			//如果既没有实现PriorityOrdered，也没有实现Ordered。加入到nonOrderedPostProcessorNames
			else {
				nonOrderedPostProcessorNames.add(ppName);
			}
		}

		// First, invoke the BeanFactoryPostProcessors that implement PriorityOrdered.
		//排序处理priorityOrderedPostProcessors，即实现了PriorityOrdered接口的BeanFactoryPostProcessor
		sortPostProcessors(priorityOrderedPostProcessors, beanFactory);
		//执行priorityOrderedPostProcessors
		invokeBeanFactoryPostProcessors(priorityOrderedPostProcessors, beanFactory);

		// Next, invoke the BeanFactoryPostProcessors that implement Ordered.
		//执行实现了Ordered接口的BeanFactoryPostProcessor
		List<BeanFactoryPostProcessor> orderedPostProcessors = new ArrayList<>();
		for (String postProcessorName : orderedPostProcessorNames) {
			orderedPostProcessors.add(beanFactory.getBean(postProcessorName, BeanFactoryPostProcessor.class));
		}
		sortPostProcessors(orderedPostProcessors, beanFactory);
		invokeBeanFactoryPostProcessors(orderedPostProcessors, beanFactory);

		// Finally, invoke all other BeanFactoryPostProcessors.
		// 执行既没有实现PriorityOrdered接口，也没有实现Ordered接口的BeanFactoryPostProcessor
		List<BeanFactoryPostProcessor> nonOrderedPostProcessors = new ArrayList<>();
		for (String postProcessorName : nonOrderedPostProcessorNames) {
			nonOrderedPostProcessors.add(beanFactory.getBean(postProcessorName, BeanFactoryPostProcessor.class));
		}
		invokeBeanFactoryPostProcessors(nonOrderedPostProcessors, beanFactory);

		// Clear cached merged bean definitions since the post-processors might have
		// modified the original metadata, e.g. replacing placeholders in values...
		// 清除了allBeanNamesByType&singletonBeanNamesByType()
		// 清除缓存中的bd，因为后处理器可能有修改了原始元数据，例如替换值中的占位符
		beanFactory.clearMetadataCache();
	}