Spring ContextRefreshedEvent事件

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遇到的单词
infrastructure ： 基础设施
arbitrary : 任何的，所有的

介绍

本文主要在观察者模式的基础上研究Spring中的事件机制

ApplicationListener监听以下4个事件：ContextStartedEvent，ContextRefreshedEvent，ContextStartedEvent，ContextClosedEvent

实现对ApplicationContext刷新或初始化时的监听，测试中未出现加载两次的情况，如果需要加入event.getApplicationContext().getParent()判断

监听ContextRefreshedEvent

@Component
public class ContextEnvent implements ApplicationListener<ContextRefreshedEvent> {
    @Override
    public void onApplicationEvent(ContextRefreshedEvent event) {
        System.out.println("Spring Refreshed");
    }
}

自从Spring 4.2以后，可以使用@EventListener注解实现，相信用过Spring-Kafka的读者不会陌生这种写法

@Component
public class AnnotateContextEvent{
    @EventListener
    public void handleRefresh(ContextRefreshedEvent event){
        System.out.println("Spring Refreshed by annotated approach");
    }
}

自定义事件

实现起来很简单，接下来尝试下Spring中的自定义事件

自定义事件需要继承ApplicationEvent，这个类并没有什么深意，只是简单封装EventObject加入了时间戳

Step 1 : 定义事件——被观察者

public class CustomerEvent extends ApplicationEvent{

    private String name;

    public CustomerEvent(Object source, String name) {
        super(source);
        this.name = name;
    }

    public String getName() {
        return name;
    }
}

Step 2 : 定义监听器——观察者

@Component
public class CustomerListener implements ApplicationListener<CustomerEvent>{
    @Override
    public void onApplicationEvent(CustomerEvent event) {
        System.out.println("CustomerListener listening： CustomerEvent has been triggered, event name is " + event.getName());
    }
}

Step 3 : 多了一步事件发布

@Component
public class CustomEventPublisher implements ApplicationEventPublisherAware {

    private ApplicationEventPublisher publisher;

    public void publish(){
        CustomerEvent customerEvent = new CustomerEvent(this,"click");
        publisher.publishEvent(customerEvent);
    }

    @Override
    public void setApplicationEventPublisher(ApplicationEventPublisher applicationEventPublisher) {
        this.publisher = applicationEventPublisher;
    }

}

测试

@SpringBootApplication
public class SpringBootDocApplication {

	public static void main(String[] args) {
		SpringApplication.run(SpringBootDocApplication.class, args)
                .getBean(CustomEventPublisher.class).publish();
	}
}

控制台输出

1	CustomerListener listening： CustomerEvent has been triggered, event name is click

如果再加入一个监听者呢？是否能通知到

@Component
public class ExtraListener implements ApplicationListener<CustomerEvent> {
    @Override
    public void onApplicationEvent(CustomerEvent event) {
        System.out.println("ExtraListener listening： CustomerEvent has been triggered, event name is " + event.getName());
    }
}

结果

1 2	CustomerListener listening： CustomerEvent has been triggered, event name is click ExtraListener listening： CustomerEvent has been triggered, event name is click