觀察者模式它的資料的變化是被動的。

觀察者模式在java中的實現：

package com.hxq.springcloud.springcloudconfigclient;

import org.springframework.context.ApplicationListener;
import org.springframework.context.annotation.AnnotationConfigApplicationContext;

public class SpringEventListenerDemo {
    public static void main(String[] args) {
        AnnotationConfigApplicationContext annotationConfigApplicationContext = new AnnotationConfigApplicationContext();

        //註冊監聽器
        annotationConfigApplicationContext.addApplicationListener(new ApplicationListener<MyApplicationEvent>() {
            /**
             * 監聽器得到事件
             * @param applicationEvent
             */
            @Override
            public void onApplicationEvent(MyApplicationEvent applicationEvent) {
                System.out.println("接收到事件："+applicationEvent.getSource());
            }
        });
        annotationConfigApplicationContext.refresh();
        //釋出事件
        annotationConfigApplicationContext.publishEvent(new MyApplicationEvent("hello world"));


    }
}

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