多线程在Spring中的使用

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"？？？

@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

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

@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

@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​​