Spring 的 ApplicationEvent and ApplicationListener .

什么是ApplicationContext?
它是Spring的核心，Context我们通常解释为上下文环境，但是理解成容器会更好些。
ApplicationContext则是应用的容器。

Spring把Bean（object）放在容器中，需要用就通过get方法取出来。

ApplicationEvent

是个抽象类，里面只有一个构造函数和一个长整型的timestamp。

ApplicationListener

是一个接口，里面只有一个onApplicationEvent方法。

所以自己的类在实现该接口的时候，要实装该方法。

如果在上下文中部署一个实现了ApplicationListener接口的bean,

那么每当在一个ApplicationEvent发布到 ApplicationContext时，
这个bean得到通知。其实这就是标准的Observer设计模式。

首先创建一个Event事件类：

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01. 1. public class EmailListEvent extends ApplicationEvent {
02. 2.
03. 3.     private static final long serialVersionUID = 1L;
04. 4.     public String address;
05. 5.     public String text;
06. 6.
07. 7.     public EmailListEvent(Object source) {
08. 8.         super(source);
09. 9.     }
10.10.
11.11.     public EmailListEvent(Object source, String address, String text) {
12.12.         super(source);
13.13.         this.address = address;
14.14.         this.text = text;
15.15.     }
16.16.
17.17.     public void print() {
18.18.         System.out.println("Hello,Spring Event!!!");
19.19.     }
20.20. }
   1. public class EmailListEvent extends ApplicationEvent {
   2.
   3.     private static final long serialVersionUID = 1L;
   4.     public String address;
   5.     public String text;
   6.
   7.     public EmailListEvent(Object source) {
   8.         super(source);
   9.     }
10.
11.     public EmailListEvent(Object source, String address, String text) {
12.         super(source);
13.         this.address = address;
14.         this.text = text;
15.     }
16.
17.     public void print() {
18.         System.out.println("Hello,Spring Event!!!");
19.     }
20. }

其次创建一个ApplicationListener类：

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01. 1. public class EmailNotifier implements ApplicationListener {
02. 2.
03. 3.     public void onApplicationEvent(ApplicationEvent evt) {
04. 4.         if (evt instanceof EmailListEvent) {
05. 5.             EmailListEvent emailEvent = (EmailListEvent) evt;
06. 6.             emailEvent.print();
07. 7.             System.out.println("the source is:" + emailEvent.getSource());
08. 8.             System.out.println("the address is:" + emailEvent.address);
09. 9.             System.out.println("the mail's context is :" + emailEvent.text);
10.10.         }
11.11.
12.12.     }
13.13. }
   1. public class EmailNotifier implements ApplicationListener {
   2.
   3.     public void onApplicationEvent(ApplicationEvent evt) {
   4.         if (evt instanceof EmailListEvent) {
   5.             EmailListEvent emailEvent = (EmailListEvent) evt;
   6.             emailEvent.print();
   7.             System.out.println("the source is:" + emailEvent.getSource());
   8.             System.out.println("the address is:" + emailEvent.address);
   9.             System.out.println("the mail's context is :" + emailEvent.text);
10.         }
11.
12.     }
13. }

接着将Listener注册到Spring的xml文件中：

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01.<?xml version="1.0" encoding="UTF-8"?>
02. <beans xmlns="http://www.springframework.org/schema/beans"
03.          xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
04.          xmlns:aop="http://www.springframework.org/schema/aop"
05.          xmlns:tx="http://www.springframework.org/schema/tx"
06.          xsi:schemaLocation="http://www.springframework.org/schema/beans
07.          http://www.springframework.org/schema/beans/spring-beans-2.0.xsd
08.          http://www.springframework.org/schema/aop
09.          http://www.springframework.org/schema/aop/spring-aop-2.0.xsd
10.          http://www.springframework.org/schema/tx
11.          http://www.springframework.org/schema/tx/spring-tx-2.0.xsd">
12.
13.     <bean id="emailListListener" class="spring.event.EmailNotifier"></bean>
14.
15.</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"
          xmlns:aop="http://www.springframework.org/schema/aop"
          xmlns:tx="http://www.springframework.org/schema/tx"
          xsi:schemaLocation="http://www.springframework.org/schema/beans
          http://www.springframework.org/schema/beans/spring-beans-2.0.xsd
          http://www.springframework.org/schema/aop
          http://www.springframework.org/schema/aop/spring-aop-2.0.xsd
          http://www.springframework.org/schema/tx
          http://www.springframework.org/schema/tx/spring-tx-2.0.xsd">

     <bean id="emailListListener" class="spring.event.EmailNotifier"></bean>

</beans>

最后创建Demo类：

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01. 1. public class ListenerEventDemo {
02. 2.
03. 3.     /**
04. 4.      * @param args
05. 5.      */
06. 6.     public static void main(String[] args) {
07. 7.         ApplicationContext context = new ClassPathXmlApplicationContext(
08. 8.                 "SpringEvent.xml");
09. 9.         EmailListEvent emailListEvent = new EmailListEvent("hello",
10.10.                 "[email protected]", "this is a test eamil content");
11.11.         //在ApplicationContext中发布一个 ApplicationEvent
12.12.         context.publishEvent(emailListEvent);
13.13.     }
14.14.
15.15. }
   1. public class ListenerEventDemo {
   2.
   3.     /**
   4.      * @param args
   5.      */
   6.     public static void main(String[] args) {
   7.         ApplicationContext context = new ClassPathXmlApplicationContext(
   8.                 "SpringEvent.xml");
   9.         EmailListEvent emailListEvent = new EmailListEvent("hello",
10.                 "[email protected]", "this is a test eamil content");
11.         //在ApplicationContext中发布一个 ApplicationEvent
12.         context.publishEvent(emailListEvent);
13.     }
14.
15. }

测试结果：

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01.# Hello,Spring Event!!!
02.# the source is:hello
03.# the address is:[email protected]
04.# the mail's context is :this is a test eamil content

Spring 的 ApplicationEvent and ApplicationListener .

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