案例1：自定义多播器和多线程有什么关系？
自定义多播器
自定义多播器如下所示，其实和我们自定义其他的不太一样，因为其他的自定义不会有value值，为什么此处必须要有value = "applicationEventMulticaster"？？？
代码语言：javascript复制@Component(value = "applicationEventMulticaster")
public class Myulticaster extends SimpleApplicationEventMulticaster{
public MyMulticaster () {
setTaskExecutor(Executors.newSingleThreadExecutor());
}
}答案在源码中
AbstractApplicationContext的initApplicationEventMulticaster()方法用于初始化Multicaster，Spring已经把多播器的名字写在源码中
代码语言：javascript复制public static final String APPLICATION_EVENT_MULTICASTER_BEAN_NAME = "applicationEventMulticaster";
protected void initApplicationEventMulticaster() {
ConfigurableListableBeanFactory beanFactory = getBeanFactory();
//如果beanFactory中有applicationEventMulticaster的bean,就把该Bean赋值给this.applicationEventMulticaster
if (beanFactory.containsLocalBean(APPLICATION_EVENT_MULTICASTER_BEAN_NAME)) {
this.applicationEventMulticaster =
beanFactory.getBean(APPLICATION_EVENT_MULTICASTER_BEAN_NAME, ApplicationEventMulticaster.class);
}
}
else {
//否则就创建一个SimpleApplicationEventMulticaster
this.applicationEventMulticaster = new SimpleApplicationEventMulticaster(beanFactory);
beanFactory.registerSingleton(APPLICATION_EVENT_MULTICASTER_BEAN_NAME, this.applicationEventMulticaster);
}
}案例
下面是自定义的listener
代码语言：javascript复制@Component
public class MyApplicationListener implements ApplicationListener<ApplicationEvent> {
@Override
public void onApplicationEvent(ApplicationEvent event) {
System.out.println("-----------MyApplicationListener-------------");
try { TimeUnit.SECONDS.sleep(3); } catch (Exception e) { e.printStackTrace(); } finally { }
System.out.println("-----------MyApplicationListener over-------------");
}
}当不不自定义多播器的时候，上面listener是同步执行的，如果定义了多波器，是异步执行的。
源码
https://github.com/cbeann/Demooo/blob/master/spring-demo/src/main/java/ioc/AppMyulticasterDemo.java
案例2:异步@Async
代码语言：javascript复制@Service
public class EmailService {
@Async
public void sendEmail() {
System.out.println("---start--");
try {
TimeUnit.SECONDS.sleep(5);
} catch (Exception e) {
e.printStackTrace();
} finally {
}
System.out.println("---end--");
}
}调用EmailService.sendEmail（）的时候是异步，也是用了线程池
源码
https://github.com/cbeann/Demooo/blob/master/springboot-demo/src/main/java/com/example/theadpool/App.java
参考
SpringIOC源码解析之--如何实现多播器的异步多播的（ApplicationEventMulticaster）_pengweismile的专栏-CSDN博客
