Spring事件机制的简单例子

本例子模拟一个给多个人发送内容（类似于报纸新闻）的例子。
1、定义事件

package com.xvshu.hello;
import org.springframework.context.ApplicationEvent;
public class ContentEvent extends ApplicationEvent {
public ContentEvent(final String content) {
super(content);
}
}

非常简单，如果用户发送内容，只需要通过构造器传入内容，然后通过getSource即可获取。
 
2、定义无序监听器
之所以说无序，类似于AOP机制，顺序是无法确定的。

package com.xvshu.hello;
import org.springframework.context.ApplicationEvent;
import org.springframework.context.ApplicationListener;
import org.springframework.stereotype.Component;
@Component
public class UserOneListener implements ApplicationListener<ApplicationEvent> {
@Override
public void onApplicationEvent(final ApplicationEvent event) {
if(event instanceof ContentEvent) {
System.out.println("[UserOneListener]msg：" + event.getSource());
}
}
}

  
1、使用@Compoent注册Bean即可；
2、在实现中需要判断event类型是ContentEvent才可以处理；
 
更简单的办法是通过泛型指定类型，如下所示

package com.xvshu.hello;
import org.springframework.context.ApplicationListener;
import org.springframework.stereotype.Component;
@Component
public class UserTwoListener implements ApplicationListener<ContentEvent> {
@Override
public void onApplicationEvent(final ContentEvent event) {
System.out.println("[UserTwoListener]msg：" + event.getSource());
}
}

 
3、定义有序监听器 
实现SmartApplicationListener接口即可。
package com.xvshu.hello;
import org.springframework.context.ApplicationEvent;
import org.springframework.context.event.SmartApplicationListener;
import org.springframework.stereotype.Component;

@Component
public class UserThreeListener implements SmartApplicationListener {

@Override
public boolean supportsEventType(final Class<? extends ApplicationEvent> eventType) {
return eventType == ContentEvent.class;
}
@Override
public boolean supportsSourceType(final Class<?> sourceType) {
return sourceType == String.class;
}
@Override
public void onApplicationEvent(final ApplicationEvent event) {
System.out.println("UserThreeListener：" + event.getSource());
}
@Override
public int getOrder() {
return 1;
}
}


package com.xvshu.hello;
import org.springframework.context.ApplicationEvent;
import org.springframework.context.event.SmartApplicationListener;
import org.springframework.stereotype.Component;

@Component
public class UserFourListener implements SmartApplicationListener {

@Override
public boolean supportsEventType(final Class<? extends ApplicationEvent> eventType) {
return eventType == ContentEvent.class;
}

@Override
public boolean supportsSourceType(final Class<?> sourceType) {
return sourceType == String.class;
}

@Override
public void onApplicationEvent(final ApplicationEvent event) {
System.out.println("[UserFourListener]msg：" + event.getSource());
}

@Override
public int getOrder() {
return 2;
}
}

supportsEventType：用于指定支持的事件类型，只有支持的才调用onApplicationEvent；
supportsSourceType：支持的目标类型，只有支持的才调用onApplicationEvent；
getOrder：即顺序，越小优先级越高

4、测试 
4.1、配置文件
Java代码

<context:component-scan base-package="com.xvshu"/>

 
就一句话，自动扫描注解Bean。
 
4.2、测试类
package com.xvshu;
import com.xvshu.hello.ContentEvent;
import org.junit.Test;
import org.junit.runner.RunWith;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.context.ApplicationContext;
import org.springframework.test.context.ContextConfiguration;
import org.springframework.test.context.junit4.SpringJUnit4ClassRunner;

@RunWith(SpringJUnit4ClassRunner.class)
@ContextConfiguration(locations={"classpath:spring-config-hello.xml"})
public class HelloIT {

@Autowired
private ApplicationContext applicationContext;
@Test
public void testPublishEvent() {
applicationContext.publishEvent(new ContentEvent("news is update"));
}

}

接着会输出：

[UserFourListener]msg：news is updat
[UserThreeListener]msg：news is update
[UserTwoListener]msg：news is updat
[UserOneListener]msg：news is updat

一个简单的测试例子就演示完毕，而且我们使用spring的事件机制去写相关代码会非常简单。