聊聊 Spring 容器启动流程

AnnotationConfigApplicationContext applicationContext =
                new AnnotationConfigApplicationContext(Config.class);

// 初始化容器
public AnnotationConfigApplicationContext(Class... annotatedClasses) {
    this();
    // 注册配置类 BeanDefinition 到容器
    register(annotatedClasses);
    // 加载或者刷新容器中的Bean
    refresh();
}

public GenericApplicationContext() {    
    this.beanFactory = new DefaultListableBeanFactory();
}

public AnnotatedBeanDefinitionReader(BeanDefinitionRegistry registry) {
		this(registry, getOrCreateEnvironment(registry));
	}

public AnnotatedBeanDefinitionReader(BeanDefinitionRegistry registry, Environment environment) {
		Assert.notNull(registry, "BeanDefinitionRegistry must not be null");
		Assert.notNull(environment, "Environment must not be null");
		this.registry = registry;
		this.conditionEvaluator = new ConditionEvaluator(registry, environment, null);
		AnnotationConfigUtils.registerAnnotationConfigProcessors(this.registry);
	}

public static void registerAnnotationConfigProcessors(BeanDefinitionRegistry registry) {
		registerAnnotationConfigProcessors(registry, null);
	}


public static Set registerAnnotationConfigProcessors(
			BeanDefinitionRegistry registry, @Nullable Object source) {

		DefaultListableBeanFactory beanFactory = unwrapDefaultListableBeanFactory(registry);
		if (beanFactory != null) {
			if (!(beanFactory.getDependencyComparator() instanceof AnnotationAwareOrderComparator)) {
				beanFactory.setDependencyComparator(AnnotationAwareOrderComparator.INSTANCE);
			}
			if (!(beanFactory.getAutowireCandidateResolver() instanceof ContextAnnotationAutowireCandidateResolver)) {
				beanFactory.setAutowireCandidateResolver(new ContextAnnotationAutowireCandidateResolver());
			}
		}

		Set beanDefs = new LinkedHashSet<>(8);

		if (!registry.containsBeanDefinition(CONFIGURATION_ANNOTATION_PROCESSOR_BEAN_NAME)) {
			RootBeanDefinition def = new RootBeanDefinition(ConfigurationClassPostProcessor.class);
			def.setSource(source);
			beanDefs.add(registerPostProcessor(registry, def, CONFIGURATION_ANNOTATION_PROCESSOR_BEAN_NAME));
		}

		if (!registry.containsBeanDefinition(AUTOWIRED_ANNOTATION_PROCESSOR_BEAN_NAME)) {
			RootBeanDefinition def = new RootBeanDefinition(AutowiredAnnotationBeanPostProcessor.class);
			def.setSource(source);
			beanDefs.add(registerPostProcessor(registry, def, AUTOWIRED_ANNOTATION_PROCESSOR_BEAN_NAME));
		}

		// Check for JSR-250 support, and if present add the CommonAnnotationBeanPostProcessor.
		if (jsr250Present && !registry.containsBeanDefinition(COMMON_ANNOTATION_PROCESSOR_BEAN_NAME)) {
			RootBeanDefinition def = new RootBeanDefinition(CommonAnnotationBeanPostProcessor.class);
			def.setSource(source);
			beanDefs.add(registerPostProcessor(registry, def, COMMON_ANNOTATION_PROCESSOR_BEAN_NAME));
		}

		// Check for JPA support, and if present add the PersistenceAnnotationBeanPostProcessor.
		if (jpaPresent && !registry.containsBeanDefinition(PERSISTENCE_ANNOTATION_PROCESSOR_BEAN_NAME)) {
			RootBeanDefinition def = new RootBeanDefinition();
			try {
				def.setBeanClass(ClassUtils.forName(PERSISTENCE_ANNOTATION_PROCESSOR_CLASS_NAME,
						AnnotationConfigUtils.class.getClassLoader()));
			}
			catch (ClassNotFoundException ex) {
				throw new IllegalStateException(
						"Cannot load optional framework class: " + PERSISTENCE_ANNOTATION_PROCESSOR_CLASS_NAME, ex);
			}
			def.setSource(source);
			beanDefs.add(registerPostProcessor(registry, def, PERSISTENCE_ANNOTATION_PROCESSOR_BEAN_NAME));
		}

		if (!registry.containsBeanDefinition(EVENT_LISTENER_PROCESSOR_BEAN_NAME)) {
			RootBeanDefinition def = new RootBeanDefinition(EventListenerMethodProcessor.class);
			def.setSource(source);
			beanDefs.add(registerPostProcessor(registry, def, EVENT_LISTENER_PROCESSOR_BEAN_NAME));
		}

		if (!registry.containsBeanDefinition(EVENT_LISTENER_FACTORY_BEAN_NAME)) {
			RootBeanDefinition def = new RootBeanDefinition(DefaultEventListenerFactory.class);
			def.setSource(source);
			beanDefs.add(registerPostProcessor(registry, def, EVENT_LISTENER_FACTORY_BEAN_NAME));
		}

		return beanDefs;
	}

 void doRegisterBean(Class annotatedClass, @Nullable Supplier instanceSupplier, @Nullable String name,
		@Nullable Class[] qualifiers, BeanDefinitionCustomizer... definitionCustomizers) {
	// 解析传入的配置类，实际上这个方法既可以解析配置类，也可以解析 Spring bean 对象
	AnnotatedGenericBeanDefinition abd = new AnnotatedGenericBeanDefinition(annotatedClass);
	// 判断是否需要跳过，判断依据是此类上有没有 @Conditional 注解
	if (this.conditionEvaluator.shouldSkip(abd.getMetadata())) {
		return;
	}

	abd.setInstanceSupplier(instanceSupplier);
	ScopeMetadata scopeMetadata = this.scopeMetadataResolver.resolveScopeMetadata(abd);
	abd.setScope(scopeMetadata.getScopeName());
	String beanName = (name != null ? name : this.beanNameGenerator.generateBeanName(abd, this.registry));
	// 处理类上的通用注解
	AnnotationConfigUtils.processCommonDefinitionAnnotations(abd);
	if (qualifiers != null) {
		for (Class qualifier : qualifiers) {
			if (Primary.class == qualifier) {
				abd.setPrimary(true);
			}
			else if (Lazy.class == qualifier) {
				abd.setLazyInit(true);
			}
			else {
				abd.addQualifier(new AutowireCandidateQualifier(qualifier));
			}
		}
	}
	// 封装成一个 BeanDefinitionHolder
	for (BeanDefinitionCustomizer customizer : definitionCustomizers) {
		customizer.customize(abd);
	}
	BeanDefinitionHolder definitionHolder = new BeanDefinitionHolder(abd, beanName);
	// 处理 scopedProxyMode
	definitionHolder = AnnotationConfigUtils.applyScopedProxyMode(scopeMetadata, definitionHolder, this.registry);

	// 把 BeanDefinitionHolder 注册到 registry
	BeanDefinitionReaderUtils.registerBeanDefinition(definitionHolder, this.registry);
}

public void refresh() throws BeansException, IllegalStateException {
	synchronized (this.startupShutdownMonitor) {
		// Prepare this context for refreshing.
		// 1. 刷新前的预处理
		prepareRefresh();

		// Tell the subclass to refresh the internal bean factory.
		// 2. 获取 beanFactory，即前面创建的【DefaultListableBeanFactory】
		ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();

		// Prepare the bean factory for use in this context.
		// 3. 预处理 beanFactory，向容器中添加一些组件
		prepareBeanFactory(beanFactory);

		try {
			// Allows post-processing of the bean factory in context subclasses.
			// 4. 子类通过重写这个方法可以在 BeanFactory 创建并与准备完成以后做进一步的设置
			postProcessBeanFactory(beanFactory);

			// Invoke factory processors registered as beans in the context.
			// 5. 执行 BeanFactoryPostProcessor 方法，beanFactory 后置处理器
			invokeBeanFactoryPostProcessors(beanFactory);

			// Register bean processors that intercept bean creation.
			// 6. 注册 BeanPostProcessors，bean 后置处理器
			registerBeanPostProcessors(beanFactory);

			// Initialize message source for this context.
			// 7. 初始化 MessageSource 组件（做国际化功能；消息绑定，消息解析）
			initMessageSource();

			// Initialize event multicaster for this context.
			// 8. 初始化事件派发器，在注册监听器时会用到
			initApplicationEventMulticaster();

			// Initialize other special beans in specific context subclasses.
			// 9. 留给子容器（子类），子类重写这个方法，在容器刷新的时候可以自定义逻辑，web 场景下会使用
			onRefresh();

			// Check for listener beans and register them.
			// 10. 注册监听器，派发之前步骤产生的一些事件（可能没有）
			registerListeners();

			// Instantiate all remaining (non-lazy-init) singletons.
			// 11. 初始化所有的非单实例 bean
			finishBeanFactoryInitialization(beanFactory);

			// Last step: publish corresponding event.
			// 12. 发布容器刷新完成事件
			finishRefresh();
		}

		...
		
	}
}

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

	// Configure the bean factory with context callbacks.
	// 添加一个 BeanPostProcessor【ApplicationContextAwareProcessor】
	beanFactory.addBeanPostProcessor(new ApplicationContextAwareProcessor(this));

	// 设置忽略自动装配的接口，即不能通过注解自动注入
	beanFactory.ignoreDependencyInterface(EnvironmentAware.class);
	beanFactory.ignoreDependencyInterface(EmbeddedValueResolverAware.class);
	beanFactory.ignoreDependencyInterface(ResourceLoaderAware.class);
	beanFactory.ignoreDependencyInterface(ApplicationEventPublisherAware.class);
	beanFactory.ignoreDependencyInterface(MessageSourceAware.class);
	beanFactory.ignoreDependencyInterface(ApplicationContextAware.class);

	// BeanFactory interface not registered as resolvable type in a plain factory.
	// MessageSource registered (and found for autowiring) as a bean.
	// 注册可以解析的自动装配类，即可以在任意组件中通过注解自动注入
	beanFactory.registerResolvableDependency(BeanFactory.class, beanFactory);
	beanFactory.registerResolvableDependency(ResourceLoader.class, this);
	beanFactory.registerResolvableDependency(ApplicationEventPublisher.class, this);
	beanFactory.registerResolvableDependency(ApplicationContext.class, this);

	// Register early post-processor for detecting inner beans as ApplicationListeners.
	// 添加一个 BeanPostProcessor【ApplicationListenerDetector】
	beanFactory.addBeanPostProcessor(new ApplicationListenerDetector(this));

	// Detect a LoadTimeWeaver and prepare for weaving, if found.
	// 添加编译时的 AspectJ
	if (beanFactory.containsBean(LOAD_TIME_WEAVER_BEAN_NAME)) {
		beanFactory.addBeanPostProcessor(new LoadTimeWeaverAwareProcessor(beanFactory));
		// Set a temporary ClassLoader for type matching.
		beanFactory.setTempClassLoader(new ContextTypeMatchClassLoader(beanFactory.getBeanClassLoader()));
	}

	// Register default environment beans.
	// 注册 environment 组件，类型是【ConfigurableEnvironment】
	if (!beanFactory.containsLocalBean(ENVIRONMENT_BEAN_NAME)) {
		beanFactory.registerSingleton(ENVIRONMENT_BEAN_NAME, getEnvironment());
	}
	// 注册 systemProperties 组件，类型是【Map】
	if (!beanFactory.containsLocalBean(SYSTEM_PROPERTIES_BEAN_NAME)) {
		beanFactory.registerSingleton(SYSTEM_PROPERTIES_BEAN_NAME, getEnvironment().getSystemProperties());
	}
	// 注册 systemEnvironment 组件，类型是【Map】
	if (!beanFactory.containsLocalBean(SYSTEM_ENVIRONMENT_BEAN_NAME)) {
		beanFactory.registerSingleton(SYSTEM_ENVIRONMENT_BEAN_NAME, getEnvironment().getSystemEnvironment());
	}
}

public static void invokeBeanFactoryPostProcessors(
		ConfigurableListableBeanFactory beanFactory, List beanFactoryPostProcessors) {
	// beanFactoryPostProcessors 这个参数是指用户通过 AnnotationConfigApplicationContext.addBeanFactoryPostProcessor() 方法手动传入的 BeanFactoryPostProcessor，没有交给 spring 管理
	// Invoke BeanDefinitionRegistryPostProcessors first, if any.
	// 代表执行过的 BeanDefinitionRegistryPostProcessor
	Set processedBeans = new HashSet<>();
 
	if (beanFactory instanceof BeanDefinitionRegistry) {
		BeanDefinitionRegistry registry = (BeanDefinitionRegistry) beanFactory;
		// 常规后置处理器集合，即实现了 BeanFactoryPostProcessor 接口
		List regularPostProcessors = new ArrayList<>();
		// 注册后置处理器集合，即实现了 BeanDefinitionRegistryPostProcessor 接口
		List registryProcessors = new ArrayList<>();
		// 处理自定义的 beanFactoryPostProcessors（指调用 context.addBeanFactoryPostProcessor() 方法），一般这里都没有
		for (BeanFactoryPostProcessor postProcessor : beanFactoryPostProcessors) {
			if (postProcessor instanceof BeanDefinitionRegistryPostProcessor) {
				BeanDefinitionRegistryPostProcessor registryProcessor =
						(BeanDefinitionRegistryPostProcessor) postProcessor;
				// 调用 postProcessBeanDefinitionRegistry 方法
				registryProcessor.postProcessBeanDefinitionRegistry(registry);
				registryProcessors.add(registryProcessor);
			}
			else {
				regularPostProcessors.add(postProcessor);
			}
		}
 
		// 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.
		// 定义一个变量 currentRegistryProcessors，表示当前要处理的 BeanFactoryPostProcessors
		List currentRegistryProcessors = new ArrayList<>();
 
		// First, invoke the BeanDefinitionRegistryPostProcessors that implement PriorityOrdered.
		// 首先，从容器中查找实现了 PriorityOrdered 接口的 BeanDefinitionRegistryPostProcessor 类型，这里只会查找出一个【ConfigurationClassPostProcessor】
		String[] postProcessorNames =
				beanFactory.getBeanNamesForType(BeanDefinitionRegistryPostProcessor.class, true, false);
		for (String ppName : postProcessorNames) {
			// 判断是否实现了 PriorityOrdered 接口
			if (beanFactory.isTypeMatch(ppName, PriorityOrdered.class)) {
				// 添加到 currentRegistryProcessors
				currentRegistryProcessors.add(beanFactory.getBean(ppName, BeanDefinitionRegistryPostProcessor.class));
				// 添加到 processedBeans，表示已经处理过这个类了
				processedBeans.add(ppName);
			}
		}
		// 设置排列顺序
		sortPostProcessors(currentRegistryProcessors, beanFactory);
		// 添加到 registry 中
		registryProcessors.addAll(currentRegistryProcessors);
		// 执行 [postProcessBeanDefinitionRegistry] 回调方法
		invokeBeanDefinitionRegistryPostProcessors(currentRegistryProcessors, registry);
		// 将 currentRegistryProcessors 变量清空，下面会继续用到
		currentRegistryProcessors.clear();
 
		// Next, invoke the BeanDefinitionRegistryPostProcessors that implement Ordered.
		// 接下来，从容器中查找实现了 Ordered 接口的 BeanDefinitionRegistryPostProcessors 类型，这里可能会查找出多个
		// 因为【ConfigurationClassPostProcessor】已经完成了 postProcessBeanDefinitionRegistry() 方法，已经向容器中完成扫描工作，所以容器会有很多个组件
		postProcessorNames = beanFactory.getBeanNamesForType(BeanDefinitionRegistryPostProcessor.class, true, false);
		for (String ppName : postProcessorNames) {
			// 判断 processedBeans 是否处理过这个类，且是否实现 Ordered 接口
			if (!processedBeans.contains(ppName) && beanFactory.isTypeMatch(ppName, Ordered.class)) {
				currentRegistryProcessors.add(beanFactory.getBean(ppName, BeanDefinitionRegistryPostProcessor.class));
				processedBeans.add(ppName);
			}
		}
		// 设置排列顺序
		sortPostProcessors(currentRegistryProcessors, beanFactory);
		// 添加到 registry 中
		registryProcessors.addAll(currentRegistryProcessors);
		// 执行 [postProcessBeanDefinitionRegistry] 回调方法
		invokeBeanDefinitionRegistryPostProcessors(currentRegistryProcessors, registry);
		// 将 currentRegistryProcessors 变量清空，下面会继续用到
		currentRegistryProcessors.clear();
 
		// Finally, invoke all other BeanDefinitionRegistryPostProcessors until no further ones appear.
		// 最后，从容器中查找剩余所有常规的 BeanDefinitionRegistryPostProcessors 类型
		boolean reiterate = true;
		while (reiterate) {
			reiterate = false;
			// 根据类型从容器中查找
			postProcessorNames = beanFactory.getBeanNamesForType(BeanDefinitionRegistryPostProcessor.class, true, false);
			for (String ppName : postProcessorNames) {
				// 判断 processedBeans 是否处理过这个类
				if (!processedBeans.contains(ppName)) {
					// 添加到 currentRegistryProcessors
					currentRegistryProcessors.add(beanFactory.getBean(ppName, BeanDefinitionRegistryPostProcessor.class));
					// 添加到 processedBeans，表示已经处理过这个类了
					processedBeans.add(ppName);
					// 将标识设置为 true，继续循环查找，可能随时因为防止下面调用了 invokeBeanDefinitionRegistryPostProcessors() 方法引入新的后置处理器
					reiterate = true;
				}
			}
			// 设置排列顺序
			sortPostProcessors(currentRegistryProcessors, beanFactory);
			// 添加到 registry 中
			registryProcessors.addAll(currentRegistryProcessors);
			// 执行 [postProcessBeanDefinitionRegistry] 回调方法
			invokeBeanDefinitionRegistryPostProcessors(currentRegistryProcessors, registry);
			// 将 currentRegistryProcessors 变量清空，因为下一次循环可能会用到
			currentRegistryProcessors.clear();
		}
 
		// Now, invoke the postProcessBeanFactory callback of all processors handled so far.
		// 现在执行 registryProcessors 的 [postProcessBeanFactory] 回调方法
		invokeBeanFactoryPostProcessors(registryProcessors, beanFactory);
		// 执行 regularPostProcessors 的 [postProcessBeanFactory] 回调方法，也包含用户手动调用 addBeanFactoryPostProcessor() 方法添加的 BeanFactoryPostProcessor
		invokeBeanFactoryPostProcessors(regularPostProcessors, beanFactory);
	}
 
	else {
		// Invoke factory processors registered with the context instance.
		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!
	// 从容器中查找实现了 BeanFactoryPostProcessor 接口的类
	String[] postProcessorNames =
			beanFactory.getBeanNamesForType(BeanFactoryPostProcessor.class, true, false);
 
	// Separate between BeanFactoryPostProcessors that implement PriorityOrdered,
	// Ordered, and the rest.
	// 表示实现了 PriorityOrdered 接口的 BeanFactoryPostProcessor
	List priorityOrderedPostProcessors = new ArrayList<>();
	// 表示实现了 Ordered 接口的 BeanFactoryPostProcessor
	List orderedPostProcessorNames = new ArrayList<>();
	// 表示剩下来的常规的 BeanFactoryPostProcessors
	List nonOrderedPostProcessorNames = new ArrayList<>();
	for (String ppName : postProcessorNames) {
		// 判断是否已经处理过，因为 postProcessorNames 其实包含了上面步骤处理过的 BeanDefinitionRegistry 类型
		if (processedBeans.contains(ppName)) {
			// skip - already processed in first phase above
		}
		// 判断是否实现了 PriorityOrdered 接口
		else if (beanFactory.isTypeMatch(ppName, PriorityOrdered.class)) {
			priorityOrderedPostProcessors.add(beanFactory.getBean(ppName, BeanFactoryPostProcessor.class));
		}
		// 判断是否实现了 Ordered 接口
		else if (beanFactory.isTypeMatch(ppName, Ordered.class)) {
			orderedPostProcessorNames.add(ppName);
		}
		// 剩下所有常规的
		else {
			nonOrderedPostProcessorNames.add(ppName);
		}
	}
 
	// First, invoke the BeanFactoryPostProcessors that implement PriorityOrdered.
	// 先将 priorityOrderedPostProcessors 集合排序
	sortPostProcessors(priorityOrderedPostProcessors, beanFactory);
	// 执行 priorityOrderedPostProcessors 的 [postProcessBeanFactory] 回调方法
	invokeBeanFactoryPostProcessors(priorityOrderedPostProcessors, beanFactory);
 
	// Next, invoke the BeanFactoryPostProcessors that implement Ordered.
	// 接下来，把 orderedPostProcessorNames 转成 orderedPostProcessors 集合
	List orderedPostProcessors = new ArrayList<>();
	for (String postProcessorName : orderedPostProcessorNames) {
		orderedPostProcessors.add(beanFactory.getBean(postProcessorName, BeanFactoryPostProcessor.class));
	}
	// 将 orderedPostProcessors 集合排序
	sortPostProcessors(orderedPostProcessors, beanFactory);
	// 执行 orderedPostProcessors 的 [postProcessBeanFactory] 回调方法
	invokeBeanFactoryPostProcessors(orderedPostProcessors, beanFactory);
 
	// Finally, invoke all other BeanFactoryPostProcessors.
	// 最后把 nonOrderedPostProcessorNames 转成 nonOrderedPostProcessors 集合，这里只有一个，myBeanFactoryPostProcessor
	List nonOrderedPostProcessors = new ArrayList<>();
	for (String postProcessorName : nonOrderedPostProcessorNames) {
		nonOrderedPostProcessors.add(beanFactory.getBean(postProcessorName, BeanFactoryPostProcessor.class));
	}
	// 执行 nonOrderedPostProcessors 的 [postProcessBeanFactory] 回调方法
	invokeBeanFactoryPostProcessors(nonOrderedPostProcessors, beanFactory);
 
	// Clear cached merged bean definitions since the post-processors might have
	// modified the original metadata, e.g. replacing placeholders in values...
	// 清除缓存
	beanFactory.clearMetadataCache();
}

（1）先执行BeanDefinitionRegistryPostProcessor： postProcessor.postProcessBeanDefinitionRegistry(registry)
    ① 获取所有的实现了BeanDefinitionRegistryPostProcessor接口类型的集合
    ② 先执行实现了PriorityOrdered优先级接口的BeanDefinitionRegistryPostProcessor
    ③ 再执行实现了Ordered顺序接口的BeanDefinitionRegistryPostProcessor
    ④ 最后执行没有实现任何优先级或者是顺序接口的BeanDefinitionRegistryPostProcessors        
（2）再执行BeanFactoryPostProcessor的方法：postProcessor.postProcessBeanFactory(beanFactory)
    ① 获取所有的实现了BeanFactoryPostProcessor接口类型的集合
    ② 先执行实现了PriorityOrdered优先级接口的BeanFactoryPostProcessor
    ③ 再执行实现了Ordered顺序接口的BeanFactoryPostProcessor
    ④ 最后执行没有实现任何优先级或者是顺序接口的BeanFactoryPostProcessor

public static void registerBeanPostProcessors(
		ConfigurableListableBeanFactory beanFactory, AbstractApplicationContext applicationContext) {
 
	// 从容器中获取 BeanPostProcessor 类型
	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.
	int beanProcessorTargetCount = beanFactory.getBeanPostProcessorCount() + 1 + postProcessorNames.length;
	// 向容器中添加【BeanPostProcessorChecker】，主要是用来检查是不是有 bean 已经初始化完成了，
	// 如果没有执行所有的 beanPostProcessor（用数量来判断），如果有就会打印一行 info 日志
	beanFactory.addBeanPostProcessor(new BeanPostProcessorChecker(beanFactory, beanProcessorTargetCount));
 
	// Separate between BeanPostProcessors that implement PriorityOrdered,
	// Ordered, and the rest.
	// 存放实现了 PriorityOrdered 接口的 BeanPostProcessor
	List priorityOrderedPostProcessors = new ArrayList<>();
	// 存放 MergedBeanDefinitionPostProcessor 类型的 BeanPostProcessor
	List internalPostProcessors = new ArrayList<>();
	// 存放实现了 Ordered 接口的 BeanPostProcessor 的 name
	List orderedPostProcessorNames = new ArrayList<>();
	// 存放剩下来普通的 BeanPostProcessor 的 name
	List nonOrderedPostProcessorNames = new ArrayList<>();
	// 从 beanFactory 中查找 postProcessorNames 里的 bean，然后放到对应的集合中
	for (String ppName : postProcessorNames) {
		// 判断有无实现 PriorityOrdered 接口
		if (beanFactory.isTypeMatch(ppName, PriorityOrdered.class)) {
			BeanPostProcessor pp = beanFactory.getBean(ppName, BeanPostProcessor.class);
			priorityOrderedPostProcessors.add(pp);
			// 如果实现了 PriorityOrdered 接口，且属于 MergedBeanDefinitionPostProcessor
			if (pp instanceof MergedBeanDefinitionPostProcessor) {
				// 把 MergedBeanDefinitionPostProcessor 类型的添加到 internalPostProcessors 集合中
				internalPostProcessors.add(pp);
			}
		}
		else if (beanFactory.isTypeMatch(ppName, Ordered.class)) {
			orderedPostProcessorNames.add(ppName);
		}
		else {
			nonOrderedPostProcessorNames.add(ppName);
		}
	}
 
	// First, register the BeanPostProcessors that implement PriorityOrdered.
	// 给 priorityOrderedPostProcessors 排序
	sortPostProcessors(priorityOrderedPostProcessors, beanFactory);
	// 先注册实现了 PriorityOrdered 接口的 beanPostProcessor
	registerBeanPostProcessors(beanFactory, priorityOrderedPostProcessors);
 
	// Next, register the BeanPostProcessors that implement Ordered.
	// 从 beanFactory 中查找 orderedPostProcessorNames 里的 bean，然后放到对应的集合中
	List orderedPostProcessors = new ArrayList<>();
	for (String ppName : orderedPostProcessorNames) {
		BeanPostProcessor pp = beanFactory.getBean(ppName, BeanPostProcessor.class);
		orderedPostProcessors.add(pp);
		if (pp instanceof MergedBeanDefinitionPostProcessor) {
			internalPostProcessors.add(pp);
		}
	}
	// 给 orderedPostProcessors 排序
	sortPostProcessors(orderedPostProcessors, beanFactory);
	// 再注册实现了 Ordered 接口的 beanPostProcessor
	registerBeanPostProcessors(beanFactory, orderedPostProcessors);
 
	// Now, register all regular BeanPostProcessors.
	List nonOrderedPostProcessors = new ArrayList<>();
	for (String ppName : nonOrderedPostProcessorNames) {
		BeanPostProcessor pp = beanFactory.getBean(ppName, BeanPostProcessor.class);
		nonOrderedPostProcessors.add(pp);
		if (pp instanceof MergedBeanDefinitionPostProcessor) {
			internalPostProcessors.add(pp);
		}
	}
	// 再注册常规的 beanPostProcessor
	registerBeanPostProcessors(beanFactory, nonOrderedPostProcessors);
 
	// Finally, re-register all internal BeanPostProcessors.
	// 排序 MergedBeanDefinitionPostProcessor 这种类型的 beanPostProcessor
	sortPostProcessors(internalPostProcessors, beanFactory);
	// 最后注册 MergedBeanDefinitionPostProcessor 类型的 beanPostProcessor
	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).
	// 给容器中添加【ApplicationListenerDetector】 beanPostProcessor，判断是不是监听器，如果是就把 bean 放到容器中保存起来
	// 此时容器中默认会有 6 个内置的 beanPostProcessor
		// 0 = {ApplicationContextAwareProcessor@1632}
		//	1 = {ConfigurationClassPostProcessor$ImportAwareBeanPostProcessor@1633}
		//	2 = {PostProcessorRegistrationDelegate$BeanPostProcessorChecker@1634}
		//	3 = {CommonAnnotationBeanPostProcessor@1635}
		//	4 = {AutowiredAnnotationBeanPostProcessor@1636}
		//	5 = {ApplicationListenerDetector@1637}
	beanFactory.addBeanPostProcessor(new ApplicationListenerDetector(applicationContext));
}

protected void initApplicationEventMulticaster() {
	// 获取 beanFactory
	ConfigurableListableBeanFactory beanFactory = getBeanFactory();
	// 看看容器中是否有自定义的 applicationEventMulticaster
	if (beanFactory.containsLocalBean(APPLICATION_EVENT_MULTICASTER_BEAN_NAME)) {
		// 有就从容器中获取赋值
		this.applicationEventMulticaster =
				beanFactory.getBean(APPLICATION_EVENT_MULTICASTER_BEAN_NAME, ApplicationEventMulticaster.class);
		if (logger.isTraceEnabled()) {
			logger.trace("Using ApplicationEventMulticaster [" + this.applicationEventMulticaster + "]");
		}
	}
	else {
		// 没有，就创建一个 SimpleApplicationEventMulticaster
		this.applicationEventMulticaster = new SimpleApplicationEventMulticaster(beanFactory);
		// 将创建的 ApplicationEventMulticaster 添加到 BeanFactory 中， 其他组件就可以自动注入了
		beanFactory.registerSingleton(APPLICATION_EVENT_MULTICASTER_BEAN_NAME, this.applicationEventMulticaster);
		if (logger.isTraceEnabled()) {
			logger.trace("No '" + APPLICATION_EVENT_MULTICASTER_BEAN_NAME + "' bean, using " +
					"[" + this.applicationEventMulticaster.getClass().getSimpleName() + "]");
		}
	}
}

protected void registerListeners() {
	// Register statically specified listeners first.
	// 获取之前步骤中保存的 ApplicationListener
	for (ApplicationListener listener : getApplicationListeners()) {
		// getApplicationEventMulticaster() 就是获取之前步骤初始化的 applicationEventMulticaster
		getApplicationEventMulticaster().addApplicationListener(listener);
	}
 
	// Do not initialize FactoryBeans here: We need to leave all regular beans
	// uninitialized to let post-processors apply to them!
	// 从容器中获取所有的 ApplicationListener
	String[] listenerBeanNames = getBeanNamesForType(ApplicationListener.class, true, false);
	for (String listenerBeanName : listenerBeanNames) {
		getApplicationEventMulticaster().addApplicationListenerBean(listenerBeanName);
	}
 
	// Publish early application events now that we finally have a multicaster...
	// 派发之前步骤产生的 application events
	Set earlyEventsToProcess = this.earlyApplicationEvents;
	this.earlyApplicationEvents = null;
	if (earlyEventsToProcess != null) {
		for (ApplicationEvent earlyEvent : earlyEventsToProcess) {
			getApplicationEventMulticaster().multicastEvent(earlyEvent);
		}
	}
}

public void preInstantiateSingletons() throws BeansException {
	if (logger.isTraceEnabled()) {
		logger.trace("Pre-instantiating singletons in " + this);
	}
 
	// Iterate over a copy to allow for init methods which in turn register new bean definitions.
	// While this may not be part of the regular factory bootstrap, it does otherwise work fine.
	// 获取容器中的所有 beanDefinitionName
	List beanNames = new ArrayList<>(this.beanDefinitionNames);
 
	// Trigger initialization of all non-lazy singleton beans...
	// 循环进行初始化和创建对象
	for (String beanName : beanNames) {
		// 获取 RootBeanDefinition，它表示自己的 BeanDefinition 和可能存在父类的 BeanDefinition 合并后的对象
		RootBeanDefinition bd = getMergedLocalBeanDefinition(beanName);
		// 如果是非抽象的，且单实例，非懒加载
		if (!bd.isAbstract() && bd.isSingleton() && !bd.isLazyInit()) {
			// 如果是 factoryBean，利用下面这种方法创建对象
			if (isFactoryBean(beanName)) {
				// 如果是 factoryBean，则 加上 &，先创建工厂 bean
				Object bean = getBean(FACTORY_BEAN_PREFIX + beanName);
				if (bean instanceof FactoryBean) {
					final FactoryBean factory = (FactoryBean) bean;
					boolean isEagerInit;
					if (System.getSecurityManager() != null && factory instanceof SmartFactoryBean) {
						isEagerInit = AccessController.doPrivileged((PrivilegedAction)
										((SmartFactoryBean) factory)::isEagerInit,
								getAccessControlContext());
					}
					else {
						isEagerInit = (factory instanceof SmartFactoryBean &&
								((SmartFactoryBean) factory).isEagerInit());
					}
					if (isEagerInit) {
						getBean(beanName);
					}
				}
			}
			else {
				// 不是工厂 bean，用这种方法创建对象
				getBean(beanName);
			}
		}
	}
 
	// Trigger post-initialization callback for all applicable beans...
	for (String beanName : beanNames) {
		Object singletonInstance = getSingleton(beanName);
		// 检查所有的 bean 是否是 SmartInitializingSingleton 接口
		if (singletonInstance instanceof SmartInitializingSingleton) {
			final SmartInitializingSingleton smartSingleton = (SmartInitializingSingleton) singletonInstance;
			if (System.getSecurityManager() != null) {
				AccessController.doPrivileged((PrivilegedAction