第四十八讲-事件监听器
第四十八讲-事件监听器
Spring当中有一个非常好的机制，就是事件。事件可以实现组件之间的解耦。本讲我们来看一下事件监听器的使用
1. 事件监听器实现1-实现ApplicationListener接口
如下面的代码:
// 事件解耦例子
@Configuration
public class A48_1 {
public static void main(String[] args) {
AnnotationConfigApplicationContext context = new AnnotationConfigApplicationContext(A48_1.class);
context.getBean(MyService.class).doBusiness();
context.close();
}
// 自定义一个事件，需要继承Spring提供的ApplicationEvent
static class MyEvent extends ApplicationEvent {
public MyEvent(Object source) { // source 事件源； 事件源是类名+方法名
super(source);
}
}
@Component
static class MyService {
private static final Logger log = LoggerFactory.getLogger(MyService.class);
// 想要发布一个事件，就要准备一个事件发布器
@Autowired
private ApplicationEventPublisher publisher;
public void doBusiness() {
log.debug("主线业务");
// 主线业务完成后需要做一些支线业务，如发现短信和发送邮箱，下面是问题代码
// 事件源
publisher.publishEvent(new MyEvent("MyService.doBusiness()"));
}
}
@Component
// 发送短信事件监听器
// 自定义事件监听器(事件消费者)需要实现Spring提供的ApplicationListener接口
static class SmsApplicationListener implements ApplicationListener<MyEvent> {
private static final Logger log = LoggerFactory.getLogger(SmsApplicationListener.class);
@Override
public void onApplicationEvent(MyEvent event) {
log.debug("发送短信");
}
}
// 发送邮箱事件监听器 --> 该监听器只会关注自己感兴趣的事件(在泛型中定义)
@Component
static class EmailApplicationListener implements ApplicationListener<MyEvent> {
private static final Logger log = LoggerFactory.getLogger(EmailApplicationListener.class);
@Override // 事件发生时执行的方法
public void onApplicationEvent(MyEvent event) {
log.debug("发送邮件");
}
}
}
2. 通过@EventListener方法
接下来我们再通过@EventListener方法来监听事件,此外我们发现主线业务，发送邮件，发送短信这三件事是同一个线程串行执行的，因此呢，我们改为异步的形式来实现：
@Configuration
public class A48_2 {
public static void main(String[] args) {
AnnotationConfigApplicationContext context = new AnnotationConfigApplicationContext(A48_2.class);
context.getBean(MyService.class).doBusiness();
context.close();
}
static class MyEvent extends ApplicationEvent {
public MyEvent(Object source) {
super(source);
}
}
@Component
static class MyService {
private static final Logger log = LoggerFactory.getLogger(MyService.class);
@Autowired
private ApplicationEventPublisher publisher;
public void doBusiness() {
log.debug("主线业务");
// 主线业务完成后需要做一些支线业务，下面是问题代码
publisher.publishEvent(new MyEvent("MyService.doBusiness()"));
}
}
@Component
static class SmsService {
private static final Logger log = LoggerFactory.getLogger(SmsService.class);
@EventListener // 监听事件,对MyService发布的事件感兴趣
public void listener(MyEvent myEvent) {
log.debug("发送短信");
}
}
@Component
static class EmailService {
private static final Logger log = LoggerFactory.getLogger(EmailService.class);
@EventListener // 监听事件,对MyService发布的事件感兴趣
public void listener(MyEvent myEvent) {
log.debug("发送邮件");
}
}
@Bean
public ThreadPoolTaskExecutor executor() {
ThreadPoolTaskExecutor executor = new ThreadPoolTaskExecutor();
executor.setCorePoolSize(3);
executor.setMaxPoolSize(10);
executor.setQueueCapacity(100);
return executor;
}
@Bean
public SimpleApplicationEventMulticaster applicationEventMulticaster(ThreadPoolTaskExecutor executor) {
SimpleApplicationEventMulticaster multicaster = new SimpleApplicationEventMulticaster();
multicaster.setTaskExecutor(executor);
return multicaster;
}
}
3. @EventListener的原理
接下来我们来研究一下@EventListener注解解析的原理，这里呢我们自定义一个注解，用来取代Spring提供的@EventListener注解来演示一遍:
package com.cherry.springa47;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.context.ApplicationEvent;
import org.springframework.context.ApplicationEventPublisher;
import org.springframework.context.ApplicationListener;
import org.springframework.context.annotation.AnnotationConfigApplicationContext;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.context.event.EventListener;
import org.springframework.context.event.SimpleApplicationEventMulticaster;
import org.springframework.scheduling.concurrent.ThreadPoolTaskExecutor;
import org.springframework.stereotype.Component;
import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.util.concurrent.ThreadPoolExecutor;
@Configuration
public class A48_2 {
public static void main(String[] args) {
AnnotationConfigApplicationContext context = new AnnotationConfigApplicationContext(A48_2.class);
for (String beanName : context.getBeanDefinitionNames()) {
Object bean = context.getBean(beanName);
// 获取该类的所有方法
for (Method method : bean.getClass().getDeclaredMethods()) {
// 判断哪个类上加上了@SmsService注解
if (method.isAnnotationPresent(MyListener.class)) {
ApplicationListener listener = new ApplicationListener() {
@Override
public void onApplicationEvent(ApplicationEvent event) {
System.out.println(event);
// 获取方法的参数类型信息(监听器方法需要的事件类型)
Class<?> eventType = method.getParameterTypes()[0];
// 判断类型是否匹配 --> 筛选事件类型
if (eventType.isAssignableFrom(event.getClass())) {
try {
method.invoke(bean, event); //反射调用
} catch (Exception e) {
e.printStackTrace();
}
}
}
};
// 让我们自己写的监听器加入到Spring容器中
context.addApplicationListener(listener);
}
}
}
context.getBean(MyService.class).doBusiness();
context.close();
}
static class MyEvent extends ApplicationEvent {
public MyEvent(Object source) {
super(source);
}
}
@Component
static class MyService {
private static final Logger log = LoggerFactory.getLogger(MyService.class);
@Autowired
private ApplicationEventPublisher publisher;
public void doBusiness() {
log.debug("主线业务");
// 主线业务完成后需要做一些支线业务，下面是问题代码
publisher.publishEvent(new MyEvent("MyService.doBusiness()"));
}
}
@Component
static class SmsService {
private static final Logger log = LoggerFactory.getLogger(SmsService.class);
@MyListener // 监听事件,对MyService发布的事件感兴趣
public void listener(MyEvent myEvent) {
log.debug("发送短信");
}
}
@Component
static class EmailService {
private static final Logger log = LoggerFactory.getLogger(EmailService.class);
@MyListener // 监听事件,对MyService发布的事件感兴趣
public void listener(MyEvent myEvent) {
log.debug("发送邮件");
}
}
@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.METHOD)
@interface MyListener {
}
@Bean
public ThreadPoolTaskExecutor executor() {
ThreadPoolTaskExecutor executor = new ThreadPoolTaskExecutor();
executor.setCorePoolSize(3);
executor.setMaxPoolSize(10);
executor.setQueueCapacity(100);
return executor;
}
@Bean
public SimpleApplicationEventMulticaster applicationEventMulticaster(ThreadPoolTaskExecutor executor) {
SimpleApplicationEventMulticaster multicaster = new SimpleApplicationEventMulticaster();
multicaster.setTaskExecutor(executor);
return multicaster;
}
}
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