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# spring event 介绍

发表于 2022-01-30 分类于 Java ， Spring 阅读次数： 阅读次数： Disqus：

spring框架中如果想使用一些一部操作，除了依赖第三方中间件的消息队列，还可以用spring自己的event，简单介绍下使用方法
首先我们可以建一个event，继承ApplicationEvent

    public class CustomSpringEvent extends ApplicationEvent {

        private String message;

        public CustomSpringEvent(Object source, String message) {
            super(source);
            this.message = message;
        }
        public String getMessage() {
            return message;
        }
    }

这个 ApplicationEvent 其实也比较简单，内部就一个 Object 类型的 source，可以自行扩展，我们在自定义的这个 Event 里加了个 Message ，只是简单介绍下使用

    public abstract class ApplicationEvent extends EventObject {
        private static final long serialVersionUID = 7099057708183571937L;
        private final long timestamp;

        public ApplicationEvent(Object source) {
            super(source);
            this.timestamp = System.currentTimeMillis();
        }

        public ApplicationEvent(Object source, Clock clock) {
            super(source);
            this.timestamp = clock.millis();
        }

        public final long getTimestamp() {
            return this.timestamp;
        }
    }

然后就是事件生产者和监听消费者

    @Component
    public class CustomSpringEventPublisher {

        @Resource
        private ApplicationEventPublisher applicationEventPublisher;

        public void publishCustomEvent(final String message) {
            System.out.println("Publishing custom event. ");
            CustomSpringEvent customSpringEvent = new CustomSpringEvent(this, message);
            applicationEventPublisher.publishEvent(customSpringEvent);
        }
    }

这里的 ApplicationEventPublisher 是 Spring 的方法接口

    @FunctionalInterface
    public interface ApplicationEventPublisher {
        default void publishEvent(ApplicationEvent event) {
            this.publishEvent((Object)event);
        }

        void publishEvent(Object var1);
    }

具体的是例如 `org.springframework.context.support.AbstractApplicationContext#publishEvent(java.lang.Object, org.springframework.core.ResolvableType)` 中的实现，后面可以展开讲讲

事件监听者：

    @Component
    public class CustomSpringEventListener implements ApplicationListener<CustomSpringEvent> {
        @Override
        public void onApplicationEvent(CustomSpringEvent event) {
            System.out.println("Received spring custom event - " + event.getMessage());
        }
    }

这里的也是 spring 的一个方法接口

    @FunctionalInterface
    public interface ApplicationListener<E extends ApplicationEvent> extends EventListener {
        void onApplicationEvent(E var1);

        static <T> ApplicationListener<PayloadApplicationEvent<T>> forPayload(Consumer<T> consumer) {
            return (event) -> {
                consumer.accept(event.getPayload());
            };
        }
    }

然后简单包个请求

    @RequestMapping(value = "/event", method = RequestMethod.GET)
    @ResponseBody
    public void event() {
        customSpringEventPublisher.publishCustomEvent("hello sprint event");
    }

就能看到接收到消息了。