spring源码解析（基于5.0.9版本）

Myth丶恋晨 2022-03-07 08:40 170阅读 0赞

本文基于web容器的spring源码解析,入口类为配置在web.xml中的监听器`ContextLoaderListener`。

下图是refresh方法的逻辑：  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9idWtlY29kZS5ibG9nLmNzZG4ubmV0_size_16_color_FFFFFF_t_70]

## 入口方法 ##

`contextInitialized`方法为初始化方法：

public void contextInitialized(ServletContextEvent event) { 
    		initWebApplicationContext(event.getServletContext());
    	}

点进`initWebApplicationContext`方法，进入了`ContextLoader`类：

public WebApplicationContext initWebApplicationContext(ServletContext servletContext) { 
    		...
    		try { 
    			// 创建一个ApplicationContext，默认是WebApplicationContext
    			if (this.context == null) { 
    				this.context = createWebApplicationContext(servletContext);
    			}
    			if (this.context instanceof ConfigurableWebApplicationContext) { 
    				ConfigurableWebApplicationContext cwac = (ConfigurableWebApplicationContext) this.context;
    				if (!cwac.isActive()) { 
    					// 第一次初始化设置父容器
    					if (cwac.getParent() == null) { 
    						cwac.setParent(parent);
    					}
    					
    					//容器初始化
    					configureAndRefreshWebApplicationContext(cwac, servletContext);
    				}
    			}
    			...
    	}

`configureAndRefreshWebApplicationContext`方法中有段代码`wac.refresh()`,调用了容器的refresh方法，这里开始真正的进行容器的初始化逻辑。

## `refresh` \- 容器的初始化 ##

`refresh`方法在类`AbstractApplicationContext`中有实现：

public void refresh() throws BeansException, IllegalStateException { 
    		synchronized (this.startupShutdownMonitor) { 
    			// 刷新前的预处理
    			prepareRefresh();
    
    			// 创建真正的容器，加载BeanDefinition并注册到BeanDefinitionRegistry
    			ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();
    
    			// 工厂的预准备工作
    			prepareBeanFactory(beanFactory);
    
    			try { 
    				// BeanFactory的后置处理
    				postProcessBeanFactory(beanFactory);
    
    				// 执行实现了BeanFactoryPostProcessor的bean
    				// 比如PropertyPlaceHoldConfigure就是在这里被调用，将xml中的${}配置替换掉
    				// BeanFactoryPostProcessor是针对BeanDefinition的操作
    				invokeBeanFactoryPostProcessors(beanFactory);
    
    				//注册BeanPostProcessor（后置处理器）
    				//比如用来实现@Autowired功能的AutowireAnnotationPostProcessor后置处理器
    				//BeanPostProcessor针对bean实例操作
    				registerBeanPostProcessors(beanFactory);
    
    				// 初始化消息源
    				initMessageSource();
    
    				// 初始化事件派发器
    				initApplicationEventMulticaster();
    
    				// 子容器实现
    				onRefresh();
    
    				// 获取注册监听
    				registerListeners();
    
    				// 初始化非懒加载的单例bean实例(non-lazy-init)
    				finishBeanFactoryInitialization(beanFactory);
    
    				// Last step: publish corresponding event.
    				finishRefresh();
    			}
    
    			catch (BeansException ex) { 
    				if (logger.isWarnEnabled()) { 
    					logger.warn("Exception encountered during context initialization - " +
    							"cancelling refresh attempt: " + ex);
    				}
    
    				// Destroy already created singletons to avoid dangling resources.
    				destroyBeans();
    
    				// Reset 'active' flag.
    				cancelRefresh(ex);
    
    				// Propagate exception to caller.
    				throw ex;
    			}
    
    			finally { 
    				// Reset common introspection caches in Spring's core, since we
    				// might not ever need metadata for singleton beans anymore...
    				resetCommonCaches();
    			}
    		}
    	}

## `prepareRefresh`\-预处理 ##

protected void prepareRefresh() { 
    		this.startupDate = System.currentTimeMillis();
    		this.closed.set(false);
    		//标记为活跃状态，该状态在容器操作中用来判断一些执行条件
    		this.active.set(true);
    
    		if (logger.isInfoEnabled()) { 
    			logger.info("Refreshing " + this);
    		}
    
    		// 初始化属性设置
    		initPropertySources();
    
    		// 检验这些属性设置是否合法
    		getEnvironment().validateRequiredProperties();
    		
    		// 用于保存容器中的一些早期的事情
    		this.earlyApplicationEvents = new LinkedHashSet<>();
    	}

在初始化化容器中，主要做了三件事情，清除web容器中的缓存，获取初始化配置，检查这些配置的合法性。

如果是注解容器`AnnotationConfigServletWebServerApplicationContext`，那么预处理中还会做一些缓存的清理动作，比如spring boot启动的web容器。由于缓存清理代码很少，这里就不贴了。

其中初始化属性设置的方法`initPropertySources()`是个模板方法，方便其他具体子类实现。

校验属性设置时，判断该配置是否合法的依据仅仅是设置项不能为空，如果为空，将会直接抛出异常，异常信息如下:

> The following properties were declared as required but could not be resolved: 【配置项名称】

## `obtainFreshBeanFactory` \- 获取BeanFactory ##

容器refresh预处理完成后，就会执行obtainFreshBeanFactory方法获取一个BeanFactory。

protected ConfigurableListableBeanFactory obtainFreshBeanFactory() { 
    		//刷新或者创建BeanFactory，其实是新建了一个
    		refreshBeanFactory();
    		//获取刚才创建的BeanFactory，就是一个简单的get方法
    		ConfigurableListableBeanFactory beanFactory = getBeanFactory();
    
    		return beanFactory;
    	}

方法`refreshBeanFactory（）`是一个抽象方法，需要子类去实现它。以`AbstractRefreshableApplicationContext`为例,做了如下事情：

> 1.  如果存在BeanFactory，销毁掉该工厂中的所有单列Bean信息，比如bean之间的依赖关系，类class信息
> 2.  将之前创建的BeanFactory序列化id清除，引用指向为null
> 3.  新建一个DefaultListableBeanFactory
> 4.  执行loadBeanDefinitions方法进行BeanDefinition的定位、载入、和注册

## `prepareBeanFactory` \- BeanFactory的预准备工作 ##

protected void prepareBeanFactory(ConfigurableListableBeanFactory beanFactory) { 
    		// 设置类加载器，表达式解析器、属性编辑器
    		beanFactory.setBeanClassLoader(getClassLoader());
    		beanFactory.setBeanExpressionResolver(new StandardBeanExpressionResolver(beanFactory.getBeanClassLoader()));
    		beanFactory.addPropertyEditorRegistrar(new ResourceEditorRegistrar(this, getEnvironment()));
    
    		// 添加一些在bean生命周期中可能要用到的东西，如ApplicationContextAwareProcessor，在bean初始化的时候判断该bean是否实现了各种类型的Aware接口
    		beanFactory.addBeanPostProcessor(new ApplicationContextAwareProcessor(this));
    		
    		// 设置需要忽略自动装配的一些接口
    		beanFactory.ignoreDependencyInterface(EnvironmentAware.class);
    		beanFactory.ignoreDependencyInterface(EmbeddedValueResolverAware.class);
    		beanFactory.ignoreDependencyInterface(ResourceLoaderAware.class);
    		beanFactory.ignoreDependencyInterface(ApplicationEventPublisherAware.class);
    		beanFactory.ignoreDependencyInterface(MessageSourceAware.class);
    		beanFactory.ignoreDependencyInterface(ApplicationContextAware.class);
    
    		// 注册可以解析的自动装配；我们能直接在任何组件中自动注入
    		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.
    		beanFactory.addBeanPostProcessor(new ApplicationListenerDetector(this));
    
    		// Detect a LoadTimeWeaver and prepare for weaving, if found.
    		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.
    		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());
    		}
    	}

`prepareBeanFactory`方法在Beanfactory生效 做些准备工作：

1.  设置BeanFactory的类加载器、表达式解析器、属性编辑器
2.  添加部分BeanPostProcessor（ApplicationContextAwareProcessor）,该处理器可以给实现了`Aware`接口的bean在创建的时候做些一些对应的装配，比如给实现了`ApplicationContextAware`接口的bean注入`applicationContext`上下文对象
3.  设置忽略的自动装配的接口EnvironmentAware、EmbeddedValueResolverAware、等，实现了这些接口的类不需要在创建的时候注入上下文
4.  注册可以解析的自动装配；我们可以在任何组件中使用`@Autowired`注解的类型属性自动注入自动值，有四种类型的属性可以自动注入：

*  BeanFactory
 *  ResourceLoader
 *  ApplicationEventPublisher
 *  ApplicationContext

1.  添加BeanPostProcessor（ApplicationListenerDetector）,该组件可以在bean初始化后做一些增强处理
2.  添加编译时的AspectJ；
3.  给BeanFactory中注册一些能用的组件；
    
     *  environment【ConfigurableEnvironment】
     *  systemProperties【Map<String, Object>】
     *  systemEnvironment【Map<String, Object>】

## `postProcessBeanFactory` \- BeanFactory创建后的后置处理（额外需要初始化的东西） ##

这也是一个空方法，让子类来重写来，处理BeanFactory创建后的额外工作。比如:

*  设置ServletContextAwareProcessor处理器
 *  像上步类似的还需要忽略需要自动装配的接口
 *  定制化容器的初始化设置

## `invokeBeanFactoryPostProcessors` \- 执行BeanFactory后置处理器 ##

`BeanFactoryPostProcessor`是BeanFactory的后置处理器，在BeanFactory标准初始化之后执行的。  
包括两个接口：

> BeanDefinitionRegistryPostProcessor  
> BeanFactoryPostProcessor

beanFactory的后置处理逻辑在`PostProcessorRegistrationDelegate`类中`invokeBeanFactoryPostProcessors`方法:

BeanDefinitionRegistry registry = (BeanDefinitionRegistry) beanFactory;
    			List<BeanFactoryPostProcessor> regularPostProcessors = new ArrayList<>();
    			List<BeanDefinitionRegistryPostProcessor> registryProcessors = new ArrayList<>();
    
    			//将俩种处理器分别取出
    			for (BeanFactoryPostProcessor postProcessor : beanFactoryPostProcessors) { 
    				if (postProcessor instanceof BeanDefinitionRegistryPostProcessor) { 
    					BeanDefinitionRegistryPostProcessor registryProcessor =
    							(BeanDefinitionRegistryPostProcessor) postProcessor;
    					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.
    			List<BeanDefinitionRegistryPostProcessor> currentRegistryProcessors = new ArrayList<>();
    
    			//先处理实现了PriorityOrdered的BeanDefinitionRegistryPostProcessor类型
    			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);
    				}
    			}
    			//把上一步挑出来的处理器根据优先级排序
    			sortPostProcessors(currentRegistryProcessors, beanFactory);
    			registryProcessors.addAll(currentRegistryProcessors);
    			//执行处理器postProcessBeanDefinitionRegistry方法
    			invokeBeanDefinitionRegistryPostProcessors(currentRegistryProcessors, registry);
    			currentRegistryProcessors.clear();
    
    			// 接下来执行实现了Ordered接口的BeanDefinitionRegistryPostProcessors
    			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();
    
    			// 最后处理剩余的BeanDefinitionRegistryPostProcessors
    			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);

以上代码很长，其实主要是对于俩种处理器分别按照实现的接口排序依次执行：

1.  先执行BeanFactoryPostProcessor类型的处理器
2.  先执行实现了PriorityOrdered接口的处理器，
3.  然后执行实现了Ordered接口的处理器
4.  最后执行剩下的处理器
5.  对于实现了同一接口的处理器集合，会先排序然后再依次执行
6.  等 BeanFactoryPostProcessor类型的处理器按以上排序规则全部执行完成后，再按着这个排序规则执行BeanFactoryPostProcessor类型的处理器

## `registerBeanPostProcessors` \- 注册bean后置处理器 ##

与BeanFactory后置处理器类似，bean后置处理器的注册也是在类`PostProcessorRegistrationDelegate`的`registerBeanPostProcessors`方法中，beanPostProcessor注册指的是将这些处理器按照一定的顺序放入容器中，并且保证他们在容器中唯一：

public static void registerBeanPostProcessors(
    			ConfigurableListableBeanFactory beanFactory, AbstractApplicationContext applicationContext) { 
    
    		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;
    		beanFactory.addBeanPostProcessor(new BeanPostProcessorChecker(beanFactory, beanProcessorTargetCount));
    
    		// 将处理器分成四类
    		//实现了PriorityOrdered，MergedBeanDefinitionPostProcessor，Ordered接口的，以及剩余的
    		List<BeanPostProcessor> priorityOrderedPostProcessors = new ArrayList<>();
    		List<BeanPostProcessor> internalPostProcessors = new ArrayList<>();
    		List<String> orderedPostProcessorNames = new ArrayList<>();
    		List<String> nonOrderedPostProcessorNames = new ArrayList<>();
    		for (String ppName : postProcessorNames) { 
    			if (beanFactory.isTypeMatch(ppName, PriorityOrdered.class)) { 
    				BeanPostProcessor pp = beanFactory.getBean(ppName, BeanPostProcessor.class);
    				priorityOrderedPostProcessors.add(pp);
    				if (pp instanceof MergedBeanDefinitionPostProcessor) { 
    					internalPostProcessors.add(pp);
    				}
    			}
    			else if (beanFactory.isTypeMatch(ppName, Ordered.class)) { 
    				orderedPostProcessorNames.add(ppName);
    			}
    			else { 
    				nonOrderedPostProcessorNames.add(ppName);
    			}
    		}
    
    		// 先注册实现了PriorityOrdered接口的
    		sortPostProcessors(priorityOrderedPostProcessors, beanFactory);
    		registerBeanPostProcessors(beanFactory, priorityOrderedPostProcessors);
    
    		// 注册实现了Ordered接口的
    		List<BeanPostProcessor> orderedPostProcessors = new ArrayList<>();
    		for (String ppName : orderedPostProcessorNames) { 
    			BeanPostProcessor pp = beanFactory.getBean(ppName, BeanPostProcessor.class);
    			orderedPostProcessors.add(pp);
    			if (pp instanceof MergedBeanDefinitionPostProcessor) { 
    				internalPostProcessors.add(pp);
    			}
    		}
    		sortPostProcessors(orderedPostProcessors, beanFactory);
    		registerBeanPostProcessors(beanFactory, orderedPostProcessors);
    
    		// 注册剩下的普通的
    		List<BeanPostProcessor> nonOrderedPostProcessors = new ArrayList<>();
    		for (String ppName : nonOrderedPostProcessorNames) { 
    			BeanPostProcessor pp = beanFactory.getBean(ppName, BeanPostProcessor.class);
    			nonOrderedPostProcessors.add(pp);
    			if (pp instanceof MergedBeanDefinitionPostProcessor) { 
    				internalPostProcessors.add(pp);
    			}
    		}
    		registerBeanPostProcessors(beanFactory, nonOrderedPostProcessors);
    
    		// 注册实现了MergedBeanDefinitionPostProcessor接口的
    		sortPostProcessors(internalPostProcessors, beanFactory);
    		registerBeanPostProcessors(beanFactory, internalPostProcessors);
    
    		// 最后手动注册一个ApplicationListenerDetector
    		beanFactory.addBeanPostProcessor(new ApplicationListenerDetector(applicationContext));
    	}

具体注册规则如下：  
1、先注册实现了`PriorityOrdered`接口的处理器  
2、注册实现了`Ordered`接口的处理器  
3、注册其余没有优先级的普通处理器  
4、再注册前面三种  
理器之前，会把实现了`MergedBeanDefinitionPostProcessor`接口的处理器额外用个集合保存，等前三种全部注册完成后，再注册这种处理器  
5、手动注册一个ApplicationListenerDetector，用来在bean创建完成后检查是否是ApplicationListeners

在这里我们有一个疑问，处理器可以同时实现排序接口和MergedBeanDefinitionPostProcessor的，或者只实现一个MergedBeanDefinitionPostProcessor接口，那么是如何保证，这个处理器最终优先级为4（MergedBeanDefinitionPostProcessor）呢。

看下容器注册处理器的方法：

public void addBeanPostProcessor(BeanPostProcessor beanPostProcessor) {
    		Assert.notNull(beanPostProcessor, "BeanPostProcessor must not be null");
    		this.beanPostProcessors.remove(beanPostProcessor);
    		this.beanPostProcessors.add(beanPostProcessor);
    		if (beanPostProcessor instanceof InstantiationAwareBeanPostProcessor) {
    			this.hasInstantiationAwareBeanPostProcessors = true;
    		}
    		if (beanPostProcessor instanceof DestructionAwareBeanPostProcessor) {
    			this.hasDestructionAwareBeanPostProcessors = true;
    		}
    	}

以上代码可以得知，在注册处理器的时候，如果发现容器中已经存在该处理器，会移除掉之前注册的，然后重新再注册一遍，这样就把之前靠前的排序移到后面了。

也就是说处理器如果实现了MergedBeanDefinitionPostProcessor接口，那么他在容器中的顺序排在其他类型的处理器之后处理器后面。

## `initMessageSource` \- 初始化MessageSource组件 ##

initMessageSource主要是初始化一些消息组件，这些组件可以用于做国际化，消息绑定解析等。

protected void initMessageSource() { 
    		ConfigurableListableBeanFactory beanFactory = getBeanFactory();
    		if (beanFactory.containsLocalBean(MESSAGE_SOURCE_BEAN_NAME)) { 
    			this.messageSource = beanFactory.getBean(MESSAGE_SOURCE_BEAN_NAME, MessageSource.class);
    			// 给HierarchicalMessageSource类型的消息设置父消息源
    			if (this.parent != null && this.messageSource instanceof HierarchicalMessageSource) { 
    				HierarchicalMessageSource hms = (HierarchicalMessageSource) this.messageSource;
    				if (hms.getParentMessageSource() == null) { 
    					hms.setParentMessageSource(getInternalParentMessageSource());
    				}
    			}
    			if (logger.isDebugEnabled()) { 
    				logger.debug("Using MessageSource [" + this.messageSource + "]");
    			}
    		}
    		else { 
    			// 默认创建一个空的消息源，使得容器可以提供getMessage方法的调用
    			DelegatingMessageSource dms = new DelegatingMessageSource();
    			dms.setParentMessageSource(getInternalParentMessageSource());
    			this.messageSource = dms;
    			beanFactory.registerSingleton(MESSAGE_SOURCE_BEAN_NAME, this.messageSource);
    			if (logger.isDebugEnabled()) { 
    				logger.debug("Unable to locate MessageSource with name '" + MESSAGE_SOURCE_BEAN_NAME +
    						"': using default [" + this.messageSource + "]");
    			}
    		}
    	}

上面代码总结如下：

1.  如果BeanFactory中注册了id为`messageSource`的bean，获取该实例
2.  尝试给该消息源设置父消息源
3.  如果BeanFactory中没有注册消息源，创建一个空的消息源，保证容器可以提供getMessage方法给其他地方调用
4.  这个新建的空消息源也会注册到BeanFactory里面去

## `8、initApplicationEventMulticaster` \- 初始化事件派发器 ##

protected void initApplicationEventMulticaster() { 
    		ConfigurableListableBeanFactory beanFactory = getBeanFactory();
    		if (beanFactory.containsLocalBean(APPLICATION_EVENT_MULTICASTER_BEAN_NAME)) { 
    			this.applicationEventMulticaster =
    					beanFactory.getBean(APPLICATION_EVENT_MULTICASTER_BEAN_NAME, ApplicationEventMulticaster.class);
    			if (logger.isDebugEnabled()) { 
    				logger.debug("Using ApplicationEventMulticaster [" + this.applicationEventMulticaster + "]");
    			}
    		}
    		else { 
    			this.applicationEventMulticaster = new SimpleApplicationEventMulticaster(beanFactory);
    			beanFactory.registerSingleton(APPLICATION_EVENT_MULTICASTER_BEAN_NAME, this.applicationEventMulticaster);
    			if (logger.isDebugEnabled()) { 
    				logger.debug("Unable to locate ApplicationEventMulticaster with name '" +
    						APPLICATION_EVENT_MULTICASTER_BEAN_NAME +
    						"': using default [" + this.applicationEventMulticaster + "]");
    			}
    		}
    	}

注册事件派发器的逻辑跟消息源类似：

1.  如果BeanFactory中注册了id为`applicationEventMulticaster`的bean，获取该实例
2.  如果不存在，创建`SimpleApplicationEventMulticaster`
3.  将该实例注册到BeanFactory中

## `onRefresh` \- 传递给子类 ##

`onRefresh` 是个空方法，给子类实现，让子类根据自己需要进行额外的初始化操作，比如初始化主题源。

## `registerListeners` \- 注册监听器 ##

protected void registerListeners() { 
    		// 先放入已经准备好的
    		for (ApplicationListener<?> listener : getApplicationListeners()) { 
    			getApplicationEventMulticaster().addApplicationListener(listener);
    		}
    
    		// 从BeanFactory中获取实现了ApplicationListener接口的监听器并注册进来
    		String[] listenerBeanNames = getBeanNamesForType(ApplicationListener.class, true, false);
    		for (String listenerBeanName : listenerBeanNames) { 
    			getApplicationEventMulticaster().addApplicationListenerBean(listenerBeanName);
    		}
    
    		//把早期的事件也注册进来
    		Set<ApplicationEvent> earlyEventsToProcess = this.earlyApplicationEvents;
    		this.earlyApplicationEvents = null;
    		if (earlyEventsToProcess != null) { 
    			for (ApplicationEvent earlyEvent : earlyEventsToProcess) { 
    				getApplicationEventMulticaster().multicastEvent(earlyEvent);
    			}
    		}
    	}

从代码可知，主要把三种监听器放入事件派发器中：

1.  已经放入容器的
2.  BeanFactory中实现了`ApplicationListener`接口的
3.  早期事件，这些事件是在容器刷新前的预处理中定义的

## `finishBeanFactoryInitialization` \- 初始化剩余的单实例bean(非懒加载) ##

protected void finishBeanFactoryInitialization(ConfigurableListableBeanFactory beanFactory) { 
    		// 初始化conversion转化器
    		if (beanFactory.containsBean(CONVERSION_SERVICE_BEAN_NAME) &&
    				beanFactory.isTypeMatch(CONVERSION_SERVICE_BEAN_NAME, ConversionService.class)) { 
    			beanFactory.setConversionService(
    					beanFactory.getBean(CONVERSION_SERVICE_BEAN_NAME, ConversionService.class));
    		}
    
    		// 如果没有bean后置处理器，注册一个默认的值解析器，这个解析器可以用来处理替换注解中的值
    		if (!beanFactory.hasEmbeddedValueResolver()) { 
    			beanFactory.addEmbeddedValueResolver(strVal -> getEnvironment().resolvePlaceholders(strVal));
    		}
    
    		//注册早期的LoadTimeWeaverAware
    		String[] weaverAwareNames = beanFactory.getBeanNamesForType(LoadTimeWeaverAware.class, false, false);
    		for (String weaverAwareName : weaverAwareNames) { 
    			getBean(weaverAwareName);
    		}
    
    		// Stop using the temporary ClassLoader for type matching.
    		beanFactory.setTempClassLoader(null);
    
    		// Allow for caching all bean definition metadata, not expecting further changes.
    		beanFactory.freezeConfiguration();
    
    		// 注册剩余的非懒加载单实例bean
    		beanFactory.preInstantiateSingletons();
    	}

`finishBeanFactoryInitialization`方法负责将剩余的非懒加载(non-lazy-init)的单实例bean初始化，包括以下几种bean:

*  `conversion`转化器
 *  如果没有bean后置处理器，注册一个默认的值解析器，用于注解的值解析（PropertyPlaceholderConfigurer），比如那些占位符的值
 *  早期的`LoadTimeWeaverAware`,他可以用于aop中的通知织入
 *  剩余的非懒加载单实例bean

其中，我们看下注册剩余非懒加载单实例bean的`beanFactory.preInstantiateSingletons()`方法中的代码：

public void preInstantiateSingletons() throws BeansException { 
    		if (logger.isDebugEnabled()) { 
    			logger.debug("Pre-instantiating singletons in " + this);
    		}
    
    		// 先把所有的bean定义名称放入副本列表中中
    		List<String> beanNames = new ArrayList<>(this.beanDefinitionNames);
    
    		// 找到并注册所有非懒加载的单实例bean
    		for (String beanName : beanNames) { 
    			//获取到这个beanName的定义信息
    			RootBeanDefinition bd = getMergedLocalBeanDefinition(beanName);
    			//非抽象，单列，非懒加载
    			if (!bd.isAbstract() && bd.isSingleton() && !bd.isLazyInit()) { 
    				if (isFactoryBean(beanName)) { 
    					Object bean = getBean(FACTORY_BEAN_PREFIX + beanName);
    					//工厂bean只初始化需要立马创建的
    					if (bean instanceof FactoryBean) { 
    						final FactoryBean<?> factory = (FactoryBean<?>) bean;
    						boolean isEagerInit;
    						if (System.getSecurityManager() != null && factory instanceof SmartFactoryBean) { 
    							isEagerInit = AccessController.doPrivileged((PrivilegedAction<Boolean>)
    											((SmartFactoryBean<?>) factory)::isEagerInit,
    									getAccessControlContext());
    						}
    						else { 
    							isEagerInit = (factory instanceof SmartFactoryBean &&
    									((SmartFactoryBean<?>) factory).isEagerInit());
    						}
    						if (isEagerInit) { 
    							getBean(beanName);
    						}
    					}
    				}
    				else { 
    					getBean(beanName);
    				}
    			}
    		}
    
    		// 设置bean初始化时的回调
    		for (String beanName : beanNames) { 
    			Object singletonInstance = getSingleton(beanName);
    			if (singletonInstance instanceof SmartInitializingSingleton) { 
    				final SmartInitializingSingleton smartSingleton = (SmartInitializingSingleton) singletonInstance;
    				if (System.getSecurityManager() != null) { 
    					AccessController.doPrivileged((PrivilegedAction<Object>) () -> { 
    						smartSingleton.afterSingletonsInstantiated();
    						return null;
    					}, getAccessControlContext());
    				}
    				else { 
    					smartSingleton.afterSingletonsInstantiated();
    				}
    			}
    		}
    	}

bean真正初始化是在`AbstractBeanFactory`类的`doGetBean`方法中：

protected <T> T doGetBean(final String name, @Nullable final Class<T> requiredType,
    			@Nullable final Object[] args, boolean typeCheckOnly) throws BeansException { 
    
    		final String beanName = transformedBeanName(name);
    		Object bean;
    
    		// 尝试从缓存中获取，如果能获取到，说明之前创建过
    		Object sharedInstance = getSingleton(beanName);
    		if (sharedInstance != null && args == null) { 
    			if (logger.isDebugEnabled()) { 
    				if (isSingletonCurrentlyInCreation(beanName)) { 
    					logger.debug("Returning eagerly cached instance of singleton bean '" + beanName +
    							"' that is not fully initialized yet - a consequence of a circular reference");
    				}
    				else { 
    					logger.debug("Returning cached instance of singleton bean '" + beanName + "'");
    				}
    			}
    			bean = getObjectForBeanInstance(sharedInstance, name, beanName, null);
    		}
    
    		else { 
    			// 未从缓存中获取到bean，开始bean的创建流程
    
    
    			if (isPrototypeCurrentlyInCreation(beanName)) { 
    				throw new BeanCurrentlyInCreationException(beanName);
    			}
    
    			// 父容器中有该BeanDefinition的话，让父容器创建该bean
    			BeanFactory parentBeanFactory = getParentBeanFactory();
    			if (parentBeanFactory != null && !containsBeanDefinition(beanName)) { 
    				// Not found -> check parent.
    				String nameToLookup = originalBeanName(name);
    				if (parentBeanFactory instanceof AbstractBeanFactory) { 
    					return ((AbstractBeanFactory) parentBeanFactory).doGetBean(
    							nameToLookup, requiredType, args, typeCheckOnly);
    				}
    				else if (args != null) { 
    					// Delegation to parent with explicit args.
    					return (T) parentBeanFactory.getBean(nameToLookup, args);
    				}
    				else { 
    					// No args -> delegate to standard getBean method.
    					return parentBeanFactory.getBean(nameToLookup, requiredType);
    				}
    			}
    
    			//标记该bean已创建
    			if (!typeCheckOnly) { 
    				markBeanAsCreated(beanName);
    			}
    
    			try { 
    				final RootBeanDefinition mbd = getMergedLocalBeanDefinition(beanName);
    				checkMergedBeanDefinition(mbd, beanName, args);
    
    				// 获取bean依赖的其他bean，如果有依赖bean的话，先把这些依赖的bean创建出来
    				String[] dependsOn = mbd.getDependsOn();
    				if (dependsOn != null) { 
    					for (String dep : dependsOn) { 
    						if (isDependent(beanName, dep)) { 
    							throw new BeanCreationException(mbd.getResourceDescription(), beanName,
    									"Circular depends-on relationship between '" + beanName + "' and '" + dep + "'");
    						}
    						registerDependentBean(dep, beanName);
    						try { 
    							getBean(dep);
    						}
    						catch (NoSuchBeanDefinitionException ex) { 
    							throw new BeanCreationException(mbd.getResourceDescription(), beanName,
    									"'" + beanName + "' depends on missing bean '" + dep + "'", ex);
    						}
    					}
    				}
    
    				// 单实例bean的创建
    				if (mbd.isSingleton()) { 
    					sharedInstance = getSingleton(beanName, () -> { 
    						try { 
    							return createBean(beanName, mbd, args);
    						}
    						catch (BeansException ex) { 
    							destroySingleton(beanName);
    							throw ex;
    						}
    					});
    					bean = getObjectForBeanInstance(sharedInstance, name, beanName, mbd);
    				}
    
    				else if (mbd.isPrototype()) { 
    					// It's a prototype -> create a new instance.
    					Object prototypeInstance = null;
    					try { 
    						beforePrototypeCreation(beanName);
    						prototypeInstance = createBean(beanName, mbd, args);
    					}
    					finally { 
    						afterPrototypeCreation(beanName);
    					}
    					bean = getObjectForBeanInstance(prototypeInstance, name, beanName, mbd);
    				}
    
    				else { 
    					String scopeName = mbd.getScope();
    					final Scope scope = this.scopes.get(scopeName);
    					if (scope == null) { 
    						throw new IllegalStateException("No Scope registered for scope name '" + scopeName + "'");
    					}
    					try { 
    						Object scopedInstance = scope.get(beanName, () -> { 
    							beforePrototypeCreation(beanName);
    							try { 
    								return createBean(beanName, mbd, args);
    							}
    							finally { 
    								afterPrototypeCreation(beanName);
    							}
    						});
    						bean = getObjectForBeanInstance(scopedInstance, name, beanName, mbd);
    					}
    					catch (IllegalStateException ex) { 
    						throw new BeanCreationException(beanName,
    								"Scope '" + scopeName + "' is not active for the current thread; consider " +
    								"defining a scoped proxy for this bean if you intend to refer to it from a singleton",
    								ex);
    					}
    				}
    			}
    			catch (BeansException ex) { 
    				cleanupAfterBeanCreationFailure(beanName);
    				throw ex;
    			}
    		}
    
    		// Check if required type matches the type of the actual bean instance.
    		if (requiredType != null && !requiredType.isInstance(bean)) { 
    			try { 
    				T convertedBean = getTypeConverter().convertIfNecessary(bean, requiredType);
    				if (convertedBean == null) { 
    					throw new BeanNotOfRequiredTypeException(name, requiredType, bean.getClass());
    				}
    				return convertedBean;
    			}
    			catch (TypeMismatchException ex) { 
    				if (logger.isDebugEnabled()) { 
    					logger.debug("Failed to convert bean '" + name + "' to required type '" +
    							ClassUtils.getQualifiedName(requiredType) + "'", ex);
    				}
    				throw new BeanNotOfRequiredTypeException(name, requiredType, bean.getClass());
    			}
    		}
    		return (T) bean;
    	}

`doGetBean`方法中的代码有点长，我们对他的功能做个简单的总结：

1.  创建前先尝试从单列bean集合中获取该bean，如果bean曾经被创建的话，会缓存到这个容器中，此时无需重复创建
2.  bean没被缓存过的话开始执行创建流程
3.  如果这个bean是在父容器中创建的，那么让父容器执行doGetBean方法
4.  给需要创建的bean做个标记，表示在创建了，防止其他线程创建该bean
5.  查找该bean依赖的其他bean，如果有依赖的，先创建这些依赖的bean
6.  执行`createBean`方法创建bean【下面会继续讲怎么】
7.  检查创建的bean是否类型匹配

类`AbstractAutowireCapableBeanFactory`的`createBean`方法在创建bean前会尝试返回一个该bean的代理对象，如果有代理对象会直接返回，没有的话会执行`doCreateBean`方法，开始bean初始化逻辑：

protected Object doCreateBean(final String beanName, final RootBeanDefinition mbd, final @Nullable Object[] args)
    			throws BeanCreationException { 
    
    		// 实例化bean
    		BeanWrapper instanceWrapper = null;
    		if (mbd.isSingleton()) { 
    			instanceWrapper = this.factoryBeanInstanceCache.remove(beanName);
    		}
    		if (instanceWrapper == null) { 
    			instanceWrapper = createBeanInstance(beanName, mbd, args);
    		}
    		final Object bean = instanceWrapper.getWrappedInstance();
    		Class<?> beanType = instanceWrapper.getWrappedClass();
    		if (beanType != NullBean.class) { 
    			mbd.resolvedTargetType = beanType;
    		}
    
    		// 允许后置处理器对bean进行增强处理
    		synchronized (mbd.postProcessingLock) { 
    			if (!mbd.postProcessed) { 
    				try { 
    					applyMergedBeanDefinitionPostProcessors(mbd, beanType, beanName);
    				}
    				catch (Throwable ex) { 
    					throw new BeanCreationException(mbd.getResourceDescription(), beanName,
    							"Post-processing of merged bean definition failed", ex);
    				}
    				mbd.postProcessed = true;
    			}
    		}
    
    		// Eagerly cache singletons to be able to resolve circular references
    		// even when triggered by lifecycle interfaces like BeanFactoryAware.
    		boolean earlySingletonExposure = (mbd.isSingleton() && this.allowCircularReferences &&
    				isSingletonCurrentlyInCreation(beanName));
    		if (earlySingletonExposure) { 
    			if (logger.isDebugEnabled()) { 
    				logger.debug("Eagerly caching bean '" + beanName +
    						"' to allow for resolving potential circular references");
    			}
    			addSingletonFactory(beanName, () -> getEarlyBeanReference(beanName, mbd, bean));
    		}
    
    		// Initialize the bean instance.
    		Object exposedObject = bean;
    		try { 
    			// 赋值填充bean中的属性
    			populateBean(beanName, mbd, instanceWrapper);
    			//bean初始化方法
    			exposedObject = initializeBean(beanName, exposedObject, mbd);
    		}
    		catch (Throwable ex) { 
    			if (ex instanceof BeanCreationException && beanName.equals(((BeanCreationException) ex).getBeanName())) { 
    				throw (BeanCreationException) ex;
    			}
    			else { 
    				throw new BeanCreationException(
    						mbd.getResourceDescription(), beanName, "Initialization of bean failed", ex);
    			}
    		}
    
    		if (earlySingletonExposure) { 
    			Object earlySingletonReference = getSingleton(beanName, false);
    			if (earlySingletonReference != null) { 
    				if (exposedObject == bean) { 
    					exposedObject = earlySingletonReference;
    				}
    				else if (!this.allowRawInjectionDespiteWrapping && hasDependentBean(beanName)) { 
    					String[] dependentBeans = getDependentBeans(beanName);
    					Set<String> actualDependentBeans = new LinkedHashSet<>(dependentBeans.length);
    					for (String dependentBean : dependentBeans) { 
    						if (!removeSingletonIfCreatedForTypeCheckOnly(dependentBean)) { 
    							actualDependentBeans.add(dependentBean);
    						}
    					}
    					if (!actualDependentBeans.isEmpty()) { 
    						throw new BeanCurrentlyInCreationException(beanName,
    								"Bean with name '" + beanName + "' has been injected into other beans [" +
    								StringUtils.collectionToCommaDelimitedString(actualDependentBeans) +
    								"] in its raw version as part of a circular reference, but has eventually been " +
    								"wrapped. This means that said other beans do not use the final version of the " +
    								"bean. This is often the result of over-eager type matching - consider using " +
    								"'getBeanNamesOfType' with the 'allowEagerInit' flag turned off, for example.");
    					}
    				}
    			}
    		}
    
    		// Register bean as disposable.
    		try { 
    			registerDisposableBeanIfNecessary(beanName, bean, mbd);
    		}
    		catch (BeanDefinitionValidationException ex) { 
    			throw new BeanCreationException(
    					mbd.getResourceDescription(), beanName, "Invalid destruction signature", ex);
    		}
    
    		return exposedObject;
    	}

逻辑如下：

1.  通过工厂方法或者构造器方法创建bean实例（这断代码很长，我们就不继续跟了，有兴趣可以自行点进去）
2.  调用`applyMergedBeanDefinitionPostProcessors`方法，执行`MergedBeanDefinitionPostProcessor`类型的后置处理器的`postProcessMergedBeanDefinition`方法
3.  调用`populateBean`方法，给bean的属性赋值
    
     *  执行`InstantiationAwareBeanPostProcessor`类型的后置处理器的`postProcessAfterInstantiation`方法
     *  执行`InstantiationAwareBeanPostProcessor`类型的后置处理器的`postProcessPropertyValues`方法
     *  执行`applyPropertyValues`方法设置值给bean
4.  调用`initializeBean`方法初始化bean
    
     *  invokeAwareMethods - 执行Aware接口的方法（BeanNameAware，BeanClassLoaderAware，BeanFactoryAware）
     *  applyBeanPostProcessorsBeforeInitialization - 执行`BeanPostProcessor`类型后置处理器的`postProcessBeforeInitialization`方法
     *  invokeInitMethods - 执行初始化方法
        
         *  如果bean实现了`InitializingBean`接口，执行afterPropertiesSet方法
         *  自定义方法，比如xml中设置`default-init-method`的值，或者`@bean`注解的`initMethod`
     *  applyBeanPostProcessorsAfterInitialization - 执行`BeanPostProcessor`类型后置处理器的`postProcessAfterInitialization`方法
5.  调用`registerDisposableBeanIfNecessary`方法注册bean销毁方法，也就是bean实现`DisposableBean`接口的`destroy`方法

bean创建出来后，会在`DefaultSingletonBeanRegistry`类中执行`addSingleton`方法，将新建出单例bean放入缓存中。

## `finishRefresh` \- 创建完成后的处理 ##

protected void finishRefresh() { 
    		// 清除容器级别的Resource缓存
    		clearResourceCaches();
    
    		// 初始化生命周期有关的后置处理器
    		initLifecycleProcessor();
    
    		// 将容器refresh这件事情传播给生命周期相关的处理器
    		/ 也就是执行这些处理器的onRefresh回调方法
    		getLifecycleProcessor().onRefresh();
    
    		// 发布容器刷新完成事件
    		publishEvent(new ContextRefreshedEvent(this));
    
    		// Participate in LiveBeansView MBean, if active.
    		LiveBeansView.registerApplicationContext(this);
    	}

五件事情：

1.  清除容器级别的Resource缓存
2.  初始化生命周期有关的后置处理器
3.  执行签名初始化的生命周期相关的后至处理器的onRefresh方法
4.  发布容器刷新完成事件
5.  把容器注册到LiveBeansView中

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