Spring及SpringBoot的事件监听Demo案例

前置

推送事件并实现监听。

项目源码地址：https://gitee.com/changluJava/demo-exer/tree/master/SpringDemo/spring-event

基础概念

在spring中，包含有事件机制，首先有一个发布事件A，接着有一个监听器B可以自动去监听这个发布事件的发布，在整个过程有3个对象：

事件本身，其实就是一个对象，这个对象对应的类要继承spring的ApplicationEvent，这样才能被spring识别。
发布事件的对象，一般都是使用ApplicationContext的publishEvent方法来发布；（对于springboot，可以通过注入形式获取）
接收（或者叫监听）事件的对象，使用onApplicationEvent方法或者使用@EventListener注解的方法；

对于SpringBoot项目，如何获取到Spring容器？

@Autowired
private ApplicationContext applicationContext;

Spring事件监听：基础实战案例

前提准备

配置spring依赖：

<dependencies>
    <dependency>
        <groupId>org.springframework</groupId>
        <artifactId>spring-context</artifactId>
        <version>5.3.2</version>
    </dependency>
</dependencies>

①自定义Spring配置类：SpringConfig

package com.changlu.config;

import org.springframework.context.annotation.ComponentScan;
import org.springframework.context.annotation.Configuration;

/**
 * @description  Spring配置类
 * @author changlu
 * @date 3/28/2024 3:10 PM
 * @version 1.0
 */
@Configuration
@ComponentScan("com.changlu")
public class SpringConfig {
}

②事件定义：MyEvent

自定义的事件需要继承ApplicationEvent，才能够作为一个事件：

package com.changlu;
import org.springframework.context.ApplicationEvent;

/**
 * @description  MyEvent 事件
 * @author changlu
 * @date 3/28/2024 3:10 PM
 * @version 1.0
 */
public class MyEvent extends ApplicationEvent {

    private String name;

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

    public String getName() {
        return name;
    }
}

③事件监听器：MyEventListener

实现指定的ApplicationListener监听器接口，并且配置好之前定义的事件：

package com.changlu;

import org.springframework.context.ApplicationListener;
import org.springframework.stereotype.Component;

/**
 * @author changlu
 * @version 1.0
 * @description MyEvent事件Listener监听器
 * @date 2024/03/28 15:06
 */
@Component
public class MyEventListener implements ApplicationListener<MyEvent> {
    @Override
    public void onApplicationEvent(MyEvent event) {
        //可以拿到这个对象，可以使用到其中的相应的事件对象
        System.out.println("名字叫做：" + event.getName());
    }
}

测试类Main

初始化spring容器，接着我们在容器中发布一个事件：

package com.changlu;

import com.changlu.config.SpringConfig;
import org.springframework.context.ApplicationContext;
import org.springframework.context.annotation.AnnotationConfigApplicationContext;

/**
 * @author changlu
 * @version 1.0
 * @description 手动获取spring容器，接着发布事件
 * @date 2024/03/28 14:44
 */
public class Main {
    public static void main(String[] args) {
        ApplicationContext context = new AnnotationConfigApplicationContext(SpringConfig.class);
        //发布事件，指定的事件为：EventTest
        context.publishEvent(new MyEvent(context, "changlu"));
    }
}

效果：可以看到当我们进行发布的时候，此时就会在相应的监听器中执行相应的业务逻辑。

SpringBoot的Application事件监听的实现方案

基础知识

SpringBoot Application共支持6种事件监听，按顺序分别是：

ApplicationEnvironmentPreparedEvent：在Spring已经准备好上下文但是上下文尚未创建的时候触发
ApplicationPreparedEvent：在Bean定义加载之后、刷新上下文之前触发
ApplicationStartedEvent：在刷新上下文之后、调用application命令之前触发
ApplicationStartingEvent：在Spring最开始启动的时候触发
ApplicationReadyEvent：在调用applicaiton命令之后触发
ApplicationFailedEvent：在启动Spring发生异常时触发

另外：

ApplicationRunner和CommandLineRunner的执行在第五步和第六步之间
Bean的创建在第三步和第四步之间
在启动类中，执行SpringApplication.run()方法后的代码，会在第六步后执行

前提准备

①环境与准备事件监听器：ApplicationEnvironmentPreparedEventListener

package com.changlu.listeners;

import org.springframework.boot.context.event.ApplicationEnvironmentPreparedEvent;
import org.springframework.context.ApplicationListener;

/**
 * @author changlu
 * @version 1.0
 * @description ApplicationEnvironmentPreparedEvent 事件监听器
 * @date 2024/03/28 15:37
 */
//@Component
public class ApplicationEnvironmentPreparedEventListener implements ApplicationListener<ApplicationEnvironmentPreparedEvent> {
    @Override
    public void onApplicationEvent(ApplicationEnvironmentPreparedEvent event) {
        System.out.println("============>>>>> ApplicationEnvironmentPreparedEvent is trigged");
        System.out.println(event.getTimestamp());
        System.out.println("============>>>>> End");
    }
}

②应用预准备事件监听器：ApplicationPreparedEventListener

package com.changlu.listeners;

import org.springframework.boot.context.event.ApplicationPreparedEvent;
import org.springframework.context.ApplicationListener;

/**
 * @author changlu
 * @version 1.0
 * @description ApplicationPreparedEvent 事件监听器
 * @date 2024/03/28 15:41
 */
//@Component
public class ApplicationPreparedEventListener implements ApplicationListener<ApplicationPreparedEvent> {
    @Override
    public void onApplicationEvent(ApplicationPreparedEvent event) {
        System.out.println("============>>>>> applicationPreparedEvent is trigged");
        System.out.println(event.getTimestamp());
        System.out.println("============>>>>> End");
    }
}

③应用启动事件监听器：ApplicationStartedEventListener（刷新上下文后）

package com.changlu.listeners;

import org.springframework.boot.context.event.ApplicationStartedEvent;
import org.springframework.context.ApplicationListener;

/**
 * @author changlu
 * @version 1.0
 * @description ApplicationStartedEvent 事件监听器
 * @date 2024/03/28 15:42
 */
//@Component
public class ApplicationStartedEventListener implements ApplicationListener<ApplicationStartedEvent> {
    @Override
    public void onApplicationEvent(ApplicationStartedEvent event) {
        System.out.println("============>>>>> applicationStartedEvent is trigged");
        System.out.println(event.getTimestamp());
        System.out.println("============>>>>> End");
    }
}

④应用启动事件中监听器：ApplicationStartingEventListener

package com.changlu.listeners;

import org.springframework.boot.context.event.ApplicationStartedEvent;
import org.springframework.context.ApplicationListener;

/**
 * @author changlu
 * @version 1.0
 * @description ApplicationStartedEvent 事件监听器
 * @date 2024/03/28 15:35
 */
//@Component
public class ApplicationStartingEventListener implements ApplicationListener<ApplicationStartedEvent> {
    @Override
    public void onApplicationEvent(ApplicationStartedEvent event) {
        System.out.println("============>>>>> applicationStartingEvent is trigged");
        System.out.println(event.getTimestamp());
        System.out.println("============>>>>> End");
    }
}

⑤应用准备事件监听器：ApplicationReadyEventListener

package com.changlu.listeners;

import org.springframework.boot.context.event.ApplicationReadyEvent;
import org.springframework.context.ApplicationListener;

/**
 * @author changlu
 * @version 1.0
 * @description ApplicationReadyEvent 事件监听器
 * @date 2024/03/28 15:43
 */
//@Component
public class ApplicationReadyEventListener implements ApplicationListener<ApplicationReadyEvent> {
    @Override
    public void onApplicationEvent(ApplicationReadyEvent event) {
        System.out.println("============>>>>> applicationReadyEvent is trigged");
        System.out.println(event.getTimestamp());
        System.out.println("============>>>>> End");
    }
}

⑥应用失败监听器：ApplicationFailedEventListener

package com.changlu.listeners;

import org.springframework.boot.context.event.ApplicationFailedEvent;
import org.springframework.context.ApplicationListener;

/**
 * @author changlu
 * @version 1.0
 * @description ApplicationFailedEvent 事件监听器
 * @date 2024/03/28 15:44
 */
//@Component
public class ApplicationFailedEventListener implements ApplicationListener<ApplicationFailedEvent> {
    @Override
    public void onApplicationEvent(ApplicationFailedEvent event) {
        System.out.println("============>>>>> ApplicationFailedEvent is trigged");
        System.out.println(event.getTimestamp());
        System.out.println("============>>>>> End");
    }
}

启动器添加监听器

package com.changlu;

import com.changlu.listeners.*;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;

/**
 * @author changlu
 * @version 1.0
 * @description SpringBoot启动类
 * @date 2024/03/28 15:33
 */
@SpringBootApplication
public class SpringBootEvent {
    public static void main(String[] args) {
        SpringApplication springApplication = new SpringApplication(SpringBootEvent.class);
        springApplication.addListeners(new ApplicationEnvironmentPreparedEventListener());
        springApplication.addListeners(new ApplicationFailedEventListener());
        springApplication.addListeners(new ApplicationPreparedEventListener());
        springApplication.addListeners(new ApplicationReadyEventListener());
        springApplication.addListeners(new ApplicationStartedEventListener());
        springApplication.addListeners(new ApplicationStartingEventListener());
        springApplication.run(args);
    }
}

若是将这么多事件以注解形式创建bean到容器当中，此时springboot启动的时候只会触发这三个事件监听器：

说明：在我司项目中主要使用到了ApplicationStartedEvent事件，只需要知道它是在在刷新上下文之后、调用application命令之前触发（此时应该是所有的bean实例都已经加载完成了）。

参考资料

[1]. spring的事件机制onApplicationEvent（非注解）和@EventListener（注解）：https://blog.csdn.net/jeffersonchern/article/details/125559289

整理者：长路时间：2024.3.28

前置

基础概念

Spring事件监听：基础实战案例

前提准备

①自定义Spring配置类：SpringConfig

②事件定义：MyEvent

③事件监听器：MyEventListener

测试类Main

SpringBoot的Application事件监听的实现方案

基础知识

前提准备

①环境与准备事件监听器：ApplicationEnvironmentPreparedEventListener

②应用预准备事件监听器：ApplicationPreparedEventListener

③应用启动事件监听器：ApplicationStartedEventListener（刷新上下文后）

④应用启动事件中监听器：ApplicationStartingEventListener

⑤应用准备事件监听器：ApplicationReadyEventListener

⑥应用失败监听器：ApplicationFailedEventListener

启动器添加监听器

参考资料

评论区请在客户端页面查看