六、spring加载过程之refresh过程(5)spring事

日期：2019-04-03

（7）initMessageSource

​ 对上下文的消息源进行初始化

protected void initMessageSource() {
        ConfigurableListableBeanFactory beanFactory = getBeanFactory();
        // messageSource 包含单例的话，检测属性是否设置
        if (beanFactory.containsLocalBean(MESSAGE_SOURCE_BEAN_NAME)) {
            this.messageSource = beanFactory.getBean(MESSAGE_SOURCE_BEAN_NAME, MessageSource.class);
            // Make MessageSource aware of parent MessageSource.
            if (this.parent != null && this.messageSource instanceof HierarchicalMessageSource) {
                HierarchicalMessageSource hms = (HierarchicalMessageSource) this.messageSource;
                // 父级消息源没有设置的，setParent
                if (hms.getParentMessageSource() == null) {
                    // Only set parent context as parent MessageSource if no parent MessageSource
                    // registered already.
                    //如果没有父MessageSource，则仅将父上下文设置为父MessageSource
                    hms.setParentMessageSource(getInternalParentMessageSource());
                }
            }
            if (logger.isDebugEnabled()) {
                logger.debug("Using MessageSource [" + this.messageSource + "]");
            }
        }
        //不包含消息源，创建
        else {
            // Use empty MessageSource to be able to accept getMessage .calls
            DelegatingMessageSource dms = new DelegatingMessageSource();
            dms.setParentMessageSource(getInternalParentMessageSource());
            this.messageSource = dms;
            //注册 messageSource 单例
            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 + "]");
            }
        }
    }

（8）initMessageSource

​ 初始化ApplicationEventMulticaster。 如果在上下文中没有定义，则使用SimpleApplicationEventMulticaster。

protected void initApplicationEventMulticaster() {
   ConfigurableListableBeanFactory beanFactory = getBeanFactory();
   // APPLICATION_EVENT_MULTICASTER_BEAN_NAME = applicationEventMulticaster
   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 + "]");
      }
   }
}

（9）initApplicationEventMulticaster

​ 初始化上下文中的事件机制的容器

protected void initApplicationEventMulticaster() {
   ConfigurableListableBeanFactory beanFactory = getBeanFactory();
   // APPLICATION_EVENT_MULTICASTER_BEAN_NAME = applicationEventMulticaster
   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 + "]");
      }
   }
}

（10）onRefresh

​ 初始化其他的特殊bean，需要用户重写。这里为空。

protected void onRefresh() throws BeansException {
   // For subclasses: do nothing by default.
}

（11） registerListeners

​ 检查监听bean并且将这些bean向容器注册，比如Dubbo服务发布的过程就是在这个时候做的，利用事件发布机制，在listener.onApplicationEvent(event) 中发布暴露服务。

protected void registerListeners() {
   // Register statically specified listeners first.
   for (ApplicationListener<?> listener : getApplicationListeners()) {
      getApplicationEventMulticaster().addApplicationListener(listener);
   }

   // Do not initialize FactoryBeans here: We need to leave all regular beans
   // uninitialized to let post-processors apply to them!
   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...
   Set<ApplicationEvent> earlyEventsToProcess = this.earlyApplicationEvents;
   this.earlyApplicationEvents = null;
   if (earlyEventsToProcess != null) {
      for (ApplicationEvent earlyEvent : earlyEventsToProcess) {
          //触发事件机制。多个事件同时触发。
         getApplicationEventMulticaster().multicastEvent(earlyEvent);
      }
   }
}

multicastEvent方法调用 multicastEvent(event, resolveDefaultEventType(event)),然后调用 invokeListener(listener, event)，接着listener.onApplicationEvent(event); 触发事件。

/**
* SimpleApplicationEventMulticaster#multicastEvent(ApplicationEvent)
*/
public void multicastEvent(ApplicationEvent event) {
   multicastEvent(event, resolveDefaultEventType(event));
}


@Override
public void multicastEvent(final ApplicationEvent event, ResolvableType eventType) {
        ResolvableType type = (eventType != null ? eventType : resolveDefaultEventType(event));
        for (final ApplicationListener<?> listener : getApplicationListeners(event, type)) {
            //是否异步
            Executor executor = getTaskExecutor();
            if (executor != null) {
                executor.execute(new Runnable() {
                    @Override
                    public void run() {
                        invokeListener(listener, event);
                    }
                });
            }
            else {
                invokeListener(listener, event);
            }
        }
    }

    
protected void invokeListener(ApplicationListener<?> listener, ApplicationEvent event) {
        ErrorHandler errorHandler = getErrorHandler();
        //是否处理异常
        if (errorHandler != null) {
            try {
                doInvokeListener(listener, event);
            }
            catch (Throwable err) {
                errorHandler.handleError(err);
            }
        }
        else {
            doInvokeListener(listener, event);
        }
    }


@SuppressWarnings({"unchecked", "rawtypes"})    
private void doInvokeListener(ApplicationListener listener, ApplicationEvent event) {
        try {
            listener.onApplicationEvent(event);
        }
        catch (ClassCastException ex) {
            String msg = ex.getMessage();
            if (msg == null || matchesClassCastMessage(msg, event.getClass())) {
                // Possibly a lambda-defined listener which we could not resolve the generic event type for
                // -> let's suppress the exception and just log a debug message.
                Log logger = LogFactory.getLog(getClass());
                if (logger.isDebugEnabled()) {
                    logger.debug("Non-matching event type for listener: " + listener, ex);
                }
            }
            else {
                throw ex;
            }
        }
    }