Spring IOC 的核心是 AbstractApplicationContext 的 refresh 方法。
其中一共有 13 個主要方法，這裡分析第 8 個：initApplicationEventMulticaster。

1 AbstractApplicationContext

1-1 初始化應用訊息廣播器

initApplicationEventMulticaster()

protected void initApplicationEventMulticaster() {
    // 獲取 Bean 工廠
    ConfigurableListableBeanFactory beanFactory = getBeanFactory();
    if (beanFactory.containsLocalBean(APPLICATION_EVENT_MULTICASTER_BEAN_NAME)) {
        this.applicationEventMulticaster =
            beanFactory.getBean(APPLICATION_EVENT_MULTICASTER_BEAN_NAME, ApplicationEventMulticaster.class);
        if (logger.isTraceEnabled()) {
            logger.trace("Using ApplicationEventMulticaster [" + this.applicationEventMulticaster + "]");
        }
    }
    else {
        // 定義應用事件多播器
        this.applicationEventMulticaster = new SimpleApplicationEventMulticaster(beanFactory);
        // 註冊單例
        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() + "]");
        }
    }
}
 

獲取 Bean 工廠 和 註冊單例 在前面已經分析過，這裡不再分析。

1-2 定義應用事件多播器

SimpleApplicationEventMulticaster(beanFactory)

2 SimpleApplicationEventMulticaster

public SimpleApplicationEventMulticaster(BeanFactory beanFactory) {
    // 設定 Bean 工廠
    setBeanFactory(beanFactory);
}

2-1 設定 Bean 工廠

public void setBeanFactory(BeanFactory beanFactory) {
   if (!(beanFactory instanceof ConfigurableBeanFactory)) {
      throw new IllegalStateException("Not running in a ConfigurableBeanFactory: " + beanFactory);
   }
   this.beanFactory = (ConfigurableBeanFactory) beanFactory;
   if (this.beanClassLoader == null) {
      this.beanClassLoader = this.beanFactory.getBeanClassLoader();
   }
}