本文章基于 Spring 5.3.15

Spring IOC 的核心是 AbstractApplicationContext 的 refresh 方法。

其中一共有 13 个主要方法，这里分析第 7 个：initMessageSource。

1 AbstractApplicationContext

1-1 初始化 message 源

initMessageSource()

protected void initMessageSource() {   // 获取 Bean 工厂   ConfigurableListableBeanFactory beanFactory = getBeanFactory();   if (beanFactory.containsLocalBean(MESSAGE_SOURCE_BEAN_NAME)) {      // 如果在配置中已经配置了 messageSource，那么将 messageSource 提取并记录在 this.messageSource 中      this.messageSource = beanFactory.getBean(MESSAGE_SOURCE_BEAN_NAME, MessageSource.class);      if (this.parent != null && this.messageSource instanceof HierarchicalMessageSource) {         HierarchicalMessageSource hms = (HierarchicalMessageSource) this.messageSource;         if (hms.getParentMessageSource() == null) {            hms.setParentMessageSource(getInternalParentMessageSource());         }      }      if (logger.isTraceEnabled()) {         logger.trace("Using MessageSource [" + this.messageSource + "]");      }   } else {      // 如果用户并没有定义配置文件，那么使用临时的 DelegatingMessageSource 以便于作为调用 getMessage 方法的返回      DelegatingMessageSource dms = new DelegatingMessageSource();      dms.setParentMessageSource(getInternalParentMessageSource());      this.messageSource = dms;      // 注册单例      beanFactory.registerSingleton(MESSAGE_SOURCE_BEAN_NAME, this.messageSource);      if (logger.isTraceEnabled()) {         logger.trace("No '" + MESSAGE_SOURCE_BEAN_NAME + "' bean, using [" + this.messageSource + "]");      }   }}

1-2 获取 Bean 工厂

getBeanFactory()

2 AbstractRefreshableApplicationContext

public final ConfigurableListableBeanFactory getBeanFactory() {   DefaultListableBeanFactory beanFactory = this.beanFactory;   if (beanFactory == null) {      throw new IllegalStateException("BeanFactory not initialized or already closed - " + "call 'refresh' before accessing beans via the ApplicationContext");   }   return beanFactory;}

if (beanFactory == null) 由于 beanFactory 已经被赋值，直接返回。

1 AbstractApplicationContext

1-2 注册单例

registerSingleton(MESSAGE_SOURCE_BEAN_NAME, this.messageSource)

3 DefaultListableBeanFactory

public void registerSingleton(String beanName, Object singletonObject) throws IllegalStateException {   // 调用父类方法   super.registerSingleton(beanName, singletonObject);   // 手动更新单例名称   updateManualSingletonNames(set -> set.add(beanName), set -> !this.beanDefinitionMap.containsKey(beanName));   // 按类型清除缓存   clearByTypeCache();}

3-1 调用父类方法

super.registerSingleton(beanName, singletonObject)

4 DefaultSingletonBeanRegistry

public void registerSingleton(String beanName, Object singletonObject) throws IllegalStateException {   Assert.notNull(beanName, "Bean name must not be null");   Assert.notNull(singletonObject, "Singleton object must not be null");   synchronized (this.singletonObjects) {      Object oldObject = this.singletonObjects.get(beanName);      if (oldObject != null) {         throw new IllegalStateException("Could not register object [" + singletonObject +               "] under bean name '" + beanName + "': there is already object [" + oldObject + "] bound");      }      // 添加单例      addSingleton(beanName, singletonObject);   }}

4-1 添加单例

addSingleton(beanName, singletonObject)

protected void addSingleton(String beanName, Object singletonObject) {   synchronized (this.singletonObjects) {      this.singletonObjects.put(beanName, singletonObject);      this.singletonFactories.remove(beanName);      this.earlySingletonObjects.remove(beanName);      this.registeredSingletons.add(beanName);   }}

3 DefaultListableBeanFactory

3-1 手动更新单例名称

updateManualSingletonNames(set -> set.add(beanName), set -> !this.beanDefinitionMap.containsKey(beanName))

private void updateManualSingletonNames(Consumer
    
     
      > action, Predicate
      
       
        > condition) {   // 如果已开始创建 Bean   if (hasBeanCreationStarted()) {      // Cannot modify startup-time collection elements anymore (for stable iteration)      synchronized (this.beanDefinitionMap) {         if (condition.test(this.manualSingletonNames)) {            Set
        
          updatedSingletons = new LinkedHashSet<>(this.manualSingletonNames);            action.accept(updatedSingletons);            this.manualSingletonNames = updatedSingletons;         }      }   }   else {      // Still in startup registration phase      if (condition.test(this.manualSingletonNames)) {         action.accept(this.manualSingletonNames);      }   }}
        
       
      
     
    

3-2 判断是否已开始创建 Bean

private final Set
    
      alreadyCreated = Collections.newSetFromMap(new ConcurrentHashMap<>(256));protected boolean hasBeanCreationStarted() {   return !this.alreadyCreated.isEmpty();}
    

3-1 按类型清除缓存

clearByTypeCache()

private void clearByTypeCache() {   this.allBeanNamesByType.clear();   this.singletonBeanNamesByType.clear();}