spring 46 事件发布器

演示

点击查看代码

 public static void main(String[] args) {
        AnnotationConfigApplicationContext context = new AnnotationConfigApplicationContext(A49.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; // applicationContext

        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 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");
        }
    }

    @Component
    static class EmailApplicationListener implements ApplicationListener<MyEvent> {
        private static final Logger log = LoggerFactory.getLogger(EmailApplicationListener.class);

        @Override
        public void onApplicationEvent(MyEvent event) {
            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 ApplicationEventMulticaster applicationEventMulticaster(ConfigurableApplicationContext context, ThreadPoolTaskExecutor executor) {
        return new AbstractApplicationEventMulticaster() {
            private List<GenericApplicationListener> listeners = new ArrayList<>();

            // 收集监听器
            public void addApplicationListenerBean(String name) {
                ApplicationListener listener = context.getBean(name, ApplicationListener.class);
                System.out.println(listener);
                // 获取该监听器支持的事件类型
                ResolvableType type = ResolvableType.forClass(listener.getClass()).getInterfaces()[0].getGeneric();
                System.out.println(type);

                // 将原始的 listener 封装为支持事件类型检查的 listener
                GenericApplicationListener genericApplicationListener = new GenericApplicationListener() {
                    // 是否支持某事件类型                真实的事件类型
                    public boolean supportsEventType(ResolvableType eventType) {
                        return type.isAssignableFrom(eventType);
                    }

                    public void onApplicationEvent(ApplicationEvent event) {
                        executor.submit(() -> listener.onApplicationEvent(event));
                    }
                };

                listeners.add(genericApplicationListener);
            }

            // 发布事件
            public void multicastEvent(ApplicationEvent event, ResolvableType eventType) {
                for (GenericApplicationListener listener : listeners) {
                    if (listener.supportsEventType(ResolvableType.forClass(event.getClass()))) {
                        listener.onApplicationEvent(event);
                    }
                }
            }
        };
    }

    abstract static class AbstractApplicationEventMulticaster implements ApplicationEventMulticaster {

        @Override
        public void addApplicationListener(ApplicationListener<?> listener) {

        }

        @Override
        public void addApplicationListenerBean(String listenerBeanName) {

        }

        @Override
        public void removeApplicationListener(ApplicationListener<?> listener) {

        }

        @Override
        public void removeApplicationListenerBean(String listenerBeanName) {

        }

        @Override
        public void removeApplicationListeners(Predicate<ApplicationListener<?>> predicate) {

        }

        @Override
        public void removeApplicationListenerBeans(Predicate<String> predicate) {

        }

        @Override
        public void removeAllListeners() {

        }

        @Override
        public void multicastEvent(ApplicationEvent event) {

        }

        @Override
        public void multicastEvent(ApplicationEvent event, ResolvableType eventType) {

        }
    }
}

// 演示事件发布器实现要点
public class TestEventPublisher {
    public static void main(String[] args) {
        GenericApplicationContext context = new GenericApplicationContext();
        context.registerBean("applicationEventMulticaster", MyApplicationEventMulticaster.class);
        context.refresh();

        context.publishEvent(new Object());
        context.publishEvent("aaaa");
        context.publishEvent(new Bean1());
    }

    interface Inter {

    }

    static class Bean1 implements Inter{

    }

    static class MyApplicationEventMulticaster implements ApplicationEventMulticaster {

        private List<ApplicationListener> listeners = new ArrayList<>();

        {
            listeners.add(new GenericApplicationListener() {
                @Override
                public void onApplicationEvent(ApplicationEvent event) {
                    if (event instanceof PayloadApplicationEvent payloadApplicationEvent) {
                        System.out.println(payloadApplicationEvent.getPayload());
                    }
                }

                @Override
                public boolean supportsEventType(ResolvableType eventType) {
                    System.out.println(eventType);
                    // eventType --> PayloadApplicationEvent<Object>, PayloadApplicationEvent<String>
                    return (Inter.class.isAssignableFrom(eventType.getGeneric().toClass()));
                }
            });
        }

        @Override
        public void addApplicationListener(ApplicationListener<?> listener) {

        }

        @Override
        public void addApplicationListenerBean(String listenerBeanName) {

        }

        @Override
        public void removeApplicationListener(ApplicationListener<?> listener) {

        }

        @Override
        public void removeApplicationListenerBean(String listenerBeanName) {

        }

        @Override
        public void removeApplicationListeners(Predicate<ApplicationListener<?>> predicate) {

        }

        @Override
        public void removeApplicationListenerBeans(Predicate<String> predicate) {

        }

        @Override
        public void removeAllListeners() {

        }

        @Override
        public void multicastEvent(ApplicationEvent event) {
            multicastEvent(event, null);
        }

        @SuppressWarnings("all")
        @Override
        public void multicastEvent(ApplicationEvent event, ResolvableType eventType) {
            listeners.stream().filter(applicationListener -> {
                        if (eventType == null) {
                            return false;
                        }
                        if (applicationListener instanceof GenericApplicationListener genericApplicationListener) {
                            return genericApplicationListener.supportsEventType(eventType);
                        }
                        return false;
                    })
                    .forEach(applicationListener -> {
                        applicationListener.onApplicationEvent(event);
                    });
        }
    }
}

小结💡

事件发布器模拟实现

1. addApplicationListenerBean 负责收集容器中的监听器
   • 监听器会统一转换为 GenericApplicationListener 对象，以支持判断事件类型
2. multicastEvent 遍历监听器集合，发布事件
   • 发布前先通过 GenericApplicationListener.supportsEventType 判断支持该事件类型才发事件
   • 可以利用线程池进行异步发事件优化
3. 如果发送的事件对象不是 ApplicationEvent 类型，Spring 会把它包装为 PayloadApplicationEvent 并用泛型技术解析事件对象的原始类型
   • 视频中未讲解