Spring入门学习笔记(3)——事件处理类

Spring中的事件处理

ApplicationContext 是Spring的核心模块,管理着Beans完整的生命周期。当加载Bean时,ApplicationContext会发布特定类型的事件。
eg:当Context启动时ContextStartEvent被发布,当关闭时,ContextStoppedEvent被发布。

ApplicationContext事件处理被ApplicationEvent类和ApplicationListener接口提供。因此,实现了ApplicationListener的bean,每次ApplicationContext发布ApplicationEvent时,Bean将会被通知。

Spring内建事件

  • ContextRefreshedEvent : 当ApplicationContext被初始化或者刷新时被发布。也可以通过调用ConfigurableApplicationContext接口的refresh()函数发起。
  • ContextStartedEvent : 当Application使用ConfigurableApplicationContext的start()方法启动时被发布。您可以轮询您的数据库,也可以在收到此事件后重新启动任何已停止的应用程序。
  • ContextStoppedEvent : 当ApplicationContext在ConfigurableApplicationContext接口上使用stop()方法停止时,就会发布这个事件。你可以在收到这个活动后做家务。
  • ContextClosedEvent : 当使用ConfigurableApplicationContext接口上的close()方法关闭ApplicationContext时,将发布此事件。一个封闭的环境到达了生命的终点;不能刷新或重新启动。
  • RequestHandledEvent : 这是一个特定于web的事件,它告诉所有bean HTTP请求已经得到了服务。

Spring的事件处理是单线程的,因此如果发布了一个事件,直到并且除非所有接收者都得到消息,否则进程将被阻塞,线程将不会继续。因此,如果要使用事件处理,那么在设计应用程序时应该小心。

监听Context事件

要想监听一个context事件,bean需要实现仅有一个方法onApplicationEvent()的ApplicationListener接口

Example

HelloWorld.java

public class HelloWorld {
   private String message;

   public void setMessage(String message){
      this.message  = message;
   }
   public void getMessage(){
      System.out.println("Your Message : " + message);
   }
}

CStartEventHandler.java

public class CStartEventHandler 
   implements ApplicationListener<ContextStartedEvent>{

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

CStopEventHandler

public class CStopEventHandler 
   implements ApplicationListener<ContextStoppedEvent>{

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

MainApp.java

public class MainApp {
   public static void main(String[] args) {
      ConfigurableApplicationContext context = 
         new ClassPathXmlApplicationContext("Beans.xml");

      // Let us raise a start event.
      context.start();
      
      HelloWorld obj = (HelloWorld) context.getBean("helloWorld");
      obj.getMessage();

      // Let us raise a stop event.
      context.stop();
   }
}

Beans

<?xml version = "1.0" encoding = "UTF-8"?>

<beans xmlns = "http://www.springframework.org/schema/beans"
   xmlns:xsi = "http://www.w3.org/2001/XMLSchema-instance"
   xsi:schemaLocation = "http://www.springframework.org/schema/beans
   http://www.springframework.org/schema/beans/spring-beans-3.0.xsd">

   <bean id = "helloWorld" class = "com.tutorialspoint.HelloWorld">
      <property name = "message" value = "Hello World!"/>
   </bean>

   <bean id = "cStartEventHandler" class = "com.tutorialspoint.CStartEventHandler"/>
   <bean id = "cStopEventHandler" class = "com.tutorialspoint.CStopEventHandler"/>

</beans>

输出:

ContextStartedEvent Received
Your Message : Hello World!
ContextStoppedEvent Received

自定义Spring事件

下边的案例将讲述如何编写和发布你自己的自定义事件

添加自定义事件CustomEvent.java,继承ApplicationEvent类

public class CustomEvent extends ApplicationEvent{
   public CustomEvent(Object source) {
      super(source);
   }
   public String toString(){
      return "My Custom Event";
   }
}

添加自定义事件发布类CustomEventPublisher.java,实现ApplicationEventPublisherAware接口

public class CustomEventPublisher implements ApplicationEventPublisherAware {
   private ApplicationEventPublisher publisher;
   
   public void setApplicationEventPublisher (ApplicationEventPublisher publisher) {
      this.publisher = publisher;
   }
   public void publish() {
      CustomEvent ce = new CustomEvent(this);
      publisher.publishEvent(ce);
   }
}

自定义事件监听处理类,实现ApplicationListener

public class CustomEventHandler implements ApplicationListener<CustomEvent> {
   public void onApplicationEvent(CustomEvent event) {
      System.out.println(event.toString());
   }
}

MainApp.java

public class MainApp {
   public static void main(String[] args) {
      ConfigurableApplicationContext context = 
         new ClassPathXmlApplicationContext("Beans.xml");
      
      CustomEventPublisher cvp = 
         (CustomEventPublisher) context.getBean("customEventPublisher");
      
      cvp.publish();  
      cvp.publish();
   }
}

Beans.xml

<beans xmlns = "http://www.springframework.org/schema/beans"
   xmlns:xsi = "http://www.w3.org/2001/XMLSchema-instance"
   xsi:schemaLocation = "http://www.springframework.org/schema/beans
   http://www.springframework.org/schema/beans/spring-beans-3.0.xsd">

   <bean id = "customEventHandler" class = "com.tutorialspoint.CustomEventHandler"/>
   <bean id = "customEventPublisher" class = "com.tutorialspoint.CustomEventPublisher"/>

</beans>

注意不要忘记添加customEventHandler,虽然在主函数中没有直接使用,但是context需要检查实现了ApplicationListener的
bean,所以需要在xml文件中,添加该bean。

输出:

my Custom Event
my Custom Event
posted @ 2018-10-14 22:03  NinWoo  阅读(...)  评论(... 编辑 收藏