spring事件公布

spring事件接口和注解

1.spring事件中，能够公布原生的对象具体，也能够通过继承ApplicationEvent实现事件类。

  1. ApplicationListener<E extends ApplicationEvent> 接口
    所有被spring托管的bean中，实现了该接口的类.
  2. @EventListener(Clazz)
    间接公布原生对象，该对象不须要继承ApplicationEvent接口。在监听该事件时，间接应用注解标注本人承受的类型即可。
@Component@Scope("prototype")public class PersonEvent {    @EventListener(Person.class)    @Order(1)    public void printPerson(Person person) throws Exception{        System.out.println(person.toString());    }    @Setter    @Getter    @ToString    public static class Person {        private String name;        private int age;        private String address;        public Person(String name, int age, String address) {            this.name = name;            this.age = age;            this.address = address;        }    }}=======private ApplicationContext applicationContext;@Test public void test(){    PersonEvent.Person person = new PersonEvent.Person("test", 3031, "wuhan");    applicationContext.publishEvent(person);}

2.异步事件和同步事件

spring事件的公布流程，ApplicationContext 继承 ApplicationEventPublisher接口，提供对外的公布接口。AbstractApplictionContext外部提供了一个applicationEventMulticaster。在容器refresh时，会执行initApplicationEventMulticaster；

 protected void initApplicationEventMulticaster() {        ConfigurableListableBeanFactory beanFactory = this.getBeanFactory();        if (beanFactory.containsLocalBean("applicationEventMulticaster")) {            this.applicationEventMulticaster = (ApplicationEventMulticaster)beanFactory.getBean("applicationEventMulticaster", ApplicationEventMulticaster.class);            if (this.logger.isTraceEnabled()) {                this.logger.trace("Using ApplicationEventMulticaster [" + this.applicationEventMulticaster + "]");            }        } else {            this.applicationEventMulticaster = new SimpleApplicationEventMulticaster(beanFactory);            beanFactory.registerSingleton("applicationEventMulticaster", this.applicationEventMulticaster);            if (this.logger.isTraceEnabled()) {                this.logger.trace("No 'applicationEventMulticaster' bean, using [" + this.applicationEventMulticaster.getClass().getSimpleName() + "]");            }        }    }

spring外部提供SimpleApplicationEventMulticaster外部的线程池没有初始化，所以spring的事件默认是同步事件。如果想要实现异步事件也很简略。间接向spring容器注册一个SimpleApplicationEventMulticaster即可。留神bean的名称为applicationEventMulticaster

@Bean(name = "applicationEventMulticaster")        public ApplicationEventMulticaster simpleApplicationEventMulticaster() {            SimpleApplicationEventMulticaster eventMulticaster                    = new SimpleApplicationEventMulticaster();            SimpleAsyncTaskExecutor simpleAsyncTaskExecutor = new SimpleAsyncTaskExecutor();            simpleAsyncTaskExecutor.setConcurrencyLimit(20);            eventMulticaster.setTaskExecutor(simpleAsyncTaskExecutor);            return eventMulticaster;        }

SimpleApplicationEventMulticaster事件散发器的散发流程

  public void multicastEvent(ApplicationEvent event, @Nullable ResolvableType eventType) {        ResolvableType type = eventType != null ? eventType : this.resolveDefaultEventType(event);        Executor executor = this.getTaskExecutor();        Iterator var5 = this.getApplicationListeners(event, type).iterator();        while(var5.hasNext()) {            ApplicationListener<?> listener = (ApplicationListener)var5.next();            if (executor != null) {                executor.execute(() -> {                    this.invokeListener(listener, event);                });            } else {                this.invokeListener(listener, event);            }        }    }

从代码中看出，只有配置了异步线程池，所有的事件都会异步执行。

存在可能的集中需要问题

  1. 同步事件时，事件监听有特定的执行程序怎么解决

    应用spring在解决监听listener时会进行sort, AnnotationAwareOrderComparator.sort(allListeners);所以能够通过@Order注解实现

  2. 如果不想所有的事件都异步执行，有些异步，有些同步怎么解决

    本人笼罩SimpleApplicationEventMulticaster的multicastEvent散发办法，比方将异步事件类型退出全局的map,在其中的就走异步，否则走同步。