浅谈Spring事件的使用

1、自定义事件

1.1、为什么要使用自定义事件

为了业务解耦

首先要了解几个概念

• 事件源：事件的触发者，发布事件（一般是广播）
• 事件
• 事件监听器：用于消费事件

比如一个注册业务，可能包含三个动作：注册、发送邮件提醒用户注册成功、发送优惠券，如果将这三个动作放在一个方法里执行，那耦合度就很大，如果发送邮件或发送优惠券等次要业务失败，会导致注册也跟着失败，这显然是灾难性的

如果利用事件机制，可以把用户注册当成一个事件，而发送邮件和发送优惠券当成两个监听器，用来监听用户注册事件，则可以避免以上问题

1.2、自定义事件实战

1.2.1、定义事件

import org.springframework.context.ApplicationEvent;

public class UserRegisterEvent extends ApplicationEvent {
    private String username;
    public UserRegisterEvent(Object source) {
        super(source);
    }

    public UserRegisterEvent(Object source,String username) {
        super(source);
        this.username = username;
    }

    public String getUsername() {
        return username;
    }

    public void setUsername(String username) {
        this.username = username;
    }
}

1.2.2、定义监听器（接口方式）

import com.asiainfo.com.springboottest.event.UserRegisterEvent;
import org.springframework.context.ApplicationListener;
import org.springframework.stereotype.Component;

@Component
@Order(1)
public class SendMailListener implements ApplicationListener<UserRegisterEvent> {
    @Override
    public void onApplicationEvent(UserRegisterEvent userRegisterEvent) {
        System.out.println("给用户["+userRegisterEvent.getUsername()+"]发送邮件成功！");
    }
}

1.2.3、定义监听器（注解方式）

import com.asiainfo.com.springboottest.event.UserRegisterEvent;
import org.springframework.context.event.EventListener;
import org.springframework.stereotype.Component;

@Component
public class UserRegisterListener {

    @EventListener
    @Order(2)
    public void sendMailListener(UserRegisterEvent userRegisterEvent) {
        System.out.println("给用户["+userRegisterEvent.getUsername()+"]发送邮件成功！");
    }
    @EventListener
    @Order(3)
    public void sendCouponsListener(UserRegisterEvent userRegisterEvent) {
        System.out.println("给用户["+userRegisterEvent.getUsername()+"]发送优惠券成功！");
    }
}

1.2.4、service层

import com.asiainfo.com.springboottest.annotation.PrintAccess;
import com.asiainfo.com.springboottest.annotation.RecordLog;
import com.asiainfo.com.springboottest.event.UserRegisterEvent;
import com.asiainfo.com.springboottest.service.IUserService;
import org.springframework.context.ApplicationEventPublisher;
import org.springframework.context.ApplicationEventPublisherAware;
import org.springframework.stereotype.Service;

import java.util.Date;

@Service
public class UserServiceImpl implements IUserService, ApplicationEventPublisherAware {
    private ApplicationEventPublisher applicationEventPublisher;

    @Override
    public void registerUser(String username) {
        System.out.println("用户["+username+"]注册成功!");
        //发布用户注册事件，事件源根据实际业务传参，不影响程序运行
        this.applicationEventPublisher.publishEvent(new UserRegisterEvent(applicationEventPublisher,username));
    }

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

1.2.5、支持异步

import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.context.event.ApplicationEventMulticaster;
import org.springframework.context.event.SimpleApplicationEventMulticaster;
import org.springframework.scheduling.concurrent.ThreadPoolExecutorFactoryBean;

import java.util.concurrent.Executor;

@Configuration
public class AsyncEventListenerConfig {

    @Bean
    public ApplicationEventMulticaster applicationEventMulticaster() {
        //创建一个事件广播器,spring内部默认用的也是SimpleApplicationEventMulticaster这个广播器
        SimpleApplicationEventMulticaster multicaster = new SimpleApplicationEventMulticaster();
        //给广播器提供一个线程池，通过这个线程池来调用事件监听器
        Executor executor = this.applicationEventMulticasterThreadPool().getObject();
        //设置异步执行器
        multicaster.setTaskExecutor(executor);
        return multicaster;
    }

    @Bean
    public ThreadPoolExecutorFactoryBean applicationEventMulticasterThreadPool() {
        ThreadPoolExecutorFactoryBean threadPoolExecutorFactory = new ThreadPoolExecutorFactoryBean();
        threadPoolExecutorFactory.setThreadNamePrefix("applicationEventMulticasterThreadPool-");
        threadPoolExecutorFactory.setCorePoolSize(5);
        return threadPoolExecutorFactory;
    }


}

2、spring自带事件

import com.asiainfo.com.springboottest.event.UserRegisterEvent;
import org.springframework.context.event.*;
import org.springframework.core.annotation.Order;
import org.springframework.stereotype.Component;

@Component
public class InnerEventListener {

    @EventListener
    public void contextRefreshedEventListener(ContextRefreshedEvent contextRefreshedEvent) {
        System.out.println("spring上下文刷新了！");
    }
    @EventListener
    public void contextStartedEventListener(ContextStartedEvent contextStartedEvent) {
        System.out.println("spring上下文开启了！");
    }
    @EventListener
    public void contextStoppedEventListener(ContextStoppedEvent contextStoppedEvent) {
        System.out.println("spring上下文停止了！");
    }
    @EventListener
    public void contextClosedEventListener(ContextClosedEvent ContextClosedEvent) {
        System.out.println("spring上下文关闭了！");
    }

}