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Spring事件处理

你已经看到了所有的章节了Spring的核心是ApplicationContext，它管理bean的整个生命周期。ApplicationContext中加载bean时发布某些类型的事件。例如，一个ContextStartedEvent是当所述上下文被启动并发布，上下文被停止ContextStoppedEvent。

事件处理中ApplicationContext 通过了ApplicationEvent类和ApplicationListener接口提供。所以，如果一个bean实现了ApplicationListener，然后每anApplicationEvent被发布到ApplicationContext的时候通知bean。

Spring提供了以下标准的事件：

S.N.Spring 内置活动及说明
1ContextRefreshedEvent
This event is published when the ApplicationContext is either initialized or refreshed. This can also be raised using the refresh() method on the ConfigurableApplicationContext interface.
2ContextStartedEvent
This event is published when the ApplicationContext is started using the start() method on theConfigurableApplicationContext interface. You can poll your database or you can re/start any stopped application after receiving this event.
3ContextStoppedEvent
This event is published when the ApplicationContext is stopped using the stop() method on the ConfigurableApplicationContext interface. You can do required housekeep work after receiving this event.
4ContextClosedEvent
This event is published when the ApplicationContext is closed using the close() method on theConfigurableApplicationContext interface. A closed context reaches its end of life; it cannot be refreshed or restarted.
5RequestHandledEvent
This is a web-specific event telling all beans that an HTTP request has been serviced.

Spring事件处理是单线程的，所以如果一个事件被发布，直至及除非所有的接收器得到的消息，该进程被阻塞并且流程将不会继续。因此，应注意在设计应用程序时，如果事件处理被使用。

 

监听上下文事件：

要监听上下文事件，一个bean应该实现ApplicationListener接口，只有一个方法onApplicationEvent()。因此，让我们写一个例子，看看如何传播的事件，以及如何可以把代码来执行基于某些事件所需的任务。

让我们使用Eclipse IDE，然后按照下面的步骤来创建一个Spring应用程序：

步骤描述
1Create a project with a name SpringExample and create a package com.zhishitu under the src folder in the created project.
2Add required Spring libraries using Add External JARs option as explained in the Spring Hello World Example chapter.
3Create Java classes HelloWorld, CStartEventHandler, CStopEventHandler and MainAppunder the com.zhishitu package.
4Create Beans configuration file Beans.xml under the src folder.
5The final step is to create the content of all the Java files and Bean Configuration file and run the application as explained below.

这里是HelloWorld.java 文件的内容：

package com.zhishitu;

public class HelloWorld {
   private String message;

   public void setMessage(String message){
      this.message  = message;
   }

   public void getMessage(){
      System.out.println("Your Message : " + message);
   }
}
知识兔

以下是CStartEventHandler.java文件的内容：

package com.zhishitu;

import org.springframework.context.ApplicationListener;
import org.springframework.context.event.ContextStartedEvent;

public class CStartEventHandler 
   implements ApplicationListener<ContextStartedEvent>{

   public void onApplicationEvent(ContextStartedEvent event) {
      System.out.println("ContextStartedEvent Received");
   }
}
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以下是CStopEventHandler.java文件的内容：

package com.zhishitu;

import org.springframework.context.ApplicationListener;
import org.springframework.context.event.ContextStoppedEvent;

public class CStopEventHandler 
   implements ApplicationListener<ContextStoppedEvent>{

   public void onApplicationEvent(ContextStoppedEvent event) {
      System.out.println("ContextStoppedEvent Received");
   }
}
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以下是MainApp.java文件的内容：

package com.zhishitu;

import org.springframework.context.ConfigurableApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;

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();
   }
}
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以下是配置文件beans.xml文件：

<?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.zhishitu.HelloWorld">
       <property name="message" value="Hello World!"/>
   </bean>

   <bean id="cStartEventHandler" 
         class="com.zhishitu.CStartEventHandler"/>

   <bean id="cStopEventHandler" 
         class="com.zhishitu.CStopEventHandler"/>

</beans>
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创建源程序和bean配置文件完成，让我们运行应用程序。如果一切顺利，这将打印以下信息：

ContextStartedEvent Received
Your Message : Hello World!
ContextStoppedEvent Received
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如果喜欢，你可以发布自己的自定义事件，以后你可以捕捉相同处理那些自定义事件动作。如果你有兴趣在编写自己的自定义事件，可以查看 Spring自定义事件

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