第十五章 Spring 事件

publishEvent(new ContextRefreshedEvent(this));

publishEvent(new ContextStartedEvent(this));

publishEvent(new ContextStoppedEvent(this));

public class CRefreshEventHandler
   implements ApplicationListener<ContextRefreshedEvent>{

   public void onApplicationEvent(ContextRefreshedEvent event) {
      System.out.println("ContextRefreshedEvent Received");
   }
}

public class CStartEventHandler 
   implements ApplicationListener<ContextStartedEvent>{

   public void onApplicationEvent(ContextStartedEvent event) {
      System.out.println("ContextStartedEvent Received");
   }
}

public class CStopEventHandler 
   implements ApplicationListener<ContextStoppedEvent>{

   public void onApplicationEvent(ContextStoppedEvent event) {
      System.out.println("ContextStoppedEvent Received");
   }
}

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
      xmlns="http://www.springframework.org/schema/beans"
      xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd">

   <bean id="cStartEventHandler" class="com.source.hot.ioc.book.event.CStartEventHandler"/>
   <bean id="cStopEventHandler" class="com.source.hot.ioc.book.event.CStopEventHandler"/>
   <bean class="com.source.hot.ioc.book.event.CRefreshEventHandler"/>
</beans>

public class EventTest {

   @Test
   void testEvent() {
      ClassPathXmlApplicationContext context = new ClassPathXmlApplicationContext("META-INF/spring-event.xml");
      context.start();
      context.stop();
      context.close();
   }
}

ContextRefreshedEvent Received
ContextStartedEvent Received
ContextStoppedEvent Received

@Override
public Object postProcessAfterInitialization(Object bean, String beanName) {
   if (bean instanceof ApplicationListener) {
      // potentially not detected as a listener by getBeanNamesForType retrieval
      Boolean flag = this.singletonNames.get(beanName);
      if (Boolean.TRUE.equals(flag)) {
         // singleton bean (top-level or inner): register on the fly
         this.applicationContext.addApplicationListener((ApplicationListener<?>) bean);
      }
      else if (Boolean.FALSE.equals(flag)) {
         if (logger.isWarnEnabled() && !this.applicationContext.containsBean(beanName)) {
            // inner bean with other scope - can't reliably process events
            logger.warn("Inner bean '" + beanName + "' implements ApplicationListener interface " +
                  "but is not reachable for event multicasting by its containing ApplicationContext " +
                  "because it does not have singleton scope. Only top-level listener beans are allowed " +
                  "to be of non-singleton scope.");
         }
         this.singletonNames.remove(beanName);
      }
   }
   return bean;
}

private final transient Map<String, Boolean> singletonNames = new ConcurrentHashMap<>(256);

@Override
public void postProcessMergedBeanDefinition(RootBeanDefinition beanDefinition, Class<?> beanType, String beanName) {
   if (ApplicationListener.class.isAssignableFrom(beanType)) {
      this.singletonNames.put(beanName, beanDefinition.isSingleton());
   }
}

private final Set<ApplicationListener<?>> applicationListeners = new LinkedHashSet<>();

@Override
public void postProcessBeforeDestruction(Object bean, String beanName) {
   if (bean instanceof ApplicationListener) {
      try {
         ApplicationEventMulticaster multicaster = this.applicationContext.getApplicationEventMulticaster();
         multicaster.removeApplicationListener((ApplicationListener<?>) bean);
         multicaster.removeApplicationListenerBean(beanName);
      }
      catch (IllegalStateException ex) {
         // ApplicationEventMulticaster not initialized yet - no need to remove a listener
      }
   }
}

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

protected Collection<ApplicationListener<?>> getApplicationListeners(
			ApplicationEvent event, ResolvableType eventType) {

    // 获取 事件源信息
    Object source = event.getSource();
    // 事件源信息类型
    Class<?> sourceType = (source != null ? source.getClass() : null);
    // 缓存对象key的创建
    ListenerCacheKey cacheKey = new ListenerCacheKey(eventType, sourceType);

    // 从容器中获取
    // Quick check for existing entry on ConcurrentHashMap...
    ListenerRetriever retriever = this.retrieverCache.get(cacheKey);
    // 不为空直接从缓存值中获取
    if (retriever != null) {
        // 从缓存值中获取 应用监听器列表
        return retriever.getApplicationListeners();
    }

    if (this.beanClassLoader == null ||
        (ClassUtils.isCacheSafe(event.getClass(), this.beanClassLoader) &&
         (sourceType == null || ClassUtils.isCacheSafe(sourceType, this.beanClassLoader)))) {
        // Fully synchronized building and caching of a ListenerRetriever
        synchronized (this.retrievalMutex) {
            retriever = this.retrieverCache.get(cacheKey);
            if (retriever != null) {
                return retriever.getApplicationListeners();
            }
            retriever = new ListenerRetriever(true);
            // 从 defaultRetriever 推算 ApplicationListener 对象
            Collection<ApplicationListener<?>> listeners =
                retrieveApplicationListeners(eventType, sourceType, retriever);
            this.retrieverCache.put(cacheKey, retriever);
            return listeners;
        }
    }
    else {
        // No ListenerRetriever caching -> no synchronization necessary
        return retrieveApplicationListeners(eventType, sourceType, null);
    }
}

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

	@SuppressWarnings({"rawtypes", "unchecked"})
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.isTraceEnabled()) {
				logger.trace("Non-matching event type for listener: " + listener, ex);
			}
		}
		else {
			throw ex;
		}
	}
}