第四十九讲-事件发布器

第四十九讲-事件发布器

本讲我们来学习一下事件发布器，考虑一下如我们自己定义一个事件发布器需要考虑哪些问题？

事件发布器对应的接口我们见过，即ApplicationEventMulticaster，我们一直用的是Spring提供的对该接口的实现SimpleApplicationEventMulticaster。

我们现在自己写一个ApplicationEventMulticaster的实现。

@Configuration
public class A49 {
    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) {
                System.out.println(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   获取所有监听器对象并收集起来，然后对每一个事件做一个遍历并发布事件
                // 判断该监听器实现了哪些接口并获取所有的泛型 --> 泛型也就是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);
                    }


                    // 调用原始的listener的onApplicationEvent方法
                    public void onApplicationEvent(ApplicationEvent event) {
                        // 使用线程池处理事件
                        executor.submit(() -> listener.onApplicationEvent(event));
                    }
                };

                listeners.add(genericApplicationListener);
            }

            // 发布事件
            public void multicastEvent(ApplicationEvent event, ResolvableType eventType) {
                for (GenericApplicationListener listener : listeners) {
                    // 检查事件是否是监听器支持的类型
                    if (listener.supportsEventType(ResolvableType.forClass(event.getClass()))) {
                        // 发布事件
                        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) {

        }
    }
}