本地异步处理，采用事件机制 可以使 代码解耦，更易读。事件机制实现模式是 观察者模式（或发布订阅模式），主要分为三部分：发布者、监听者、事件。
Guava EventBus
Guava EventBus实现是观察者模式，用法很简单，先上代码。
/** * Desc: 事件对象 */@Data@NoArgsConstructor@AllArgsConstructorpublic class HelloEvent { private String eventName;} @Data@NoArgsConstructorpublic class WorldEvent extends HelloEvent { private int eventNo; public WorldEvent(String name, int no) { setEventName(name); setEventNo(no); }} /** * Desc: 事件监听器，可以监听多个事件。处理方法添加 @Subscribe 注解即可。 */public class GeventListener { /** * 监听 HelloEvent 类型及其父类型（Object）的事件 */ @Subscribe public void processEvent(HelloEvent event){ System.out.println("process hello event, name:" + event.getEventName()); } /** * 监听 WorldEvent 类型及其父类型（HelloEvent 和 Object）的事件 */ @Subscribe public void processWorldEvent(WorldEvent event) { System.out.println("process world eventV1, no:" + event.getEventNo() + ", name:" + event.getEventName()); } /** * 注册多个监听器 监听同一事件 * @param event */ @Subscribe public void processWorldEventV2(WorldEvent event) { System.out.println("process world eventV2, no:" + event.getEventNo() + ", name:" + event.getEventName()); } @Subscribe public void processObject(Object object) { System.out.println("process common event, class:" + object.getClass().getSimpleName()); }} public class GuavaTest { public static void main(String[] args) { EventBus eventBus = new EventBus(); GeventListener listener = new GeventListener(); eventBus.register(listener); eventBus.post(new HelloEvent("hello")); eventBus.post(new WorldEvent("world", 23333)); }}
结果如下：
//HelloEvent被两个监听器处理（HelloEvent类及Object类的监听器）process hello event, name:helloprocess common event, class:HelloEvent//WorldEvent被四个监听器处理（两个自己的，两个父类的）process world eventV1, no:23333, name:worldprocess world eventV2, no:23333, name:worldprocess hello event, name:worldprocess common event, class:WorldEvent
由上可知：Guava EventBus把类当做事件，是以class为key注册和管理事件的，value是事件监听器的method；事件监听器只处理某一类（及其父类）事件。
事件注册与发布
//com.google.common.eventbus.EventBus#register public void register(Object object) { //key为Class， value为EventSubscriber(Object target, Method method)【集合】。注意这里Multimap 为HashMultimap， 即HashMap<K, Collection<V>> Multimap<Class<?>, EventSubscriber> methodsInListener = finder.findAllSubscribers(object); subscribersByTypeLock.writeLock().lock(); try { subscribersByType.putAll(methodsInListener); } finally { subscribersByTypeLock.writeLock().unlock(); } }//com.google.common.eventbus.EventBus#post public void post(Object event) { //找到event类及其所有父类 Set<Class<?>> dispatchTypes = flattenHierarchy(event.getClass()); boolean dispatched = false; for (Class<?> eventType : dispatchTypes) { subscribersByTypeLock.readLock().lock(); try { //找到所有事件订阅者（事件监听器） Set<EventSubscriber> wrappers = subscribersByType.get(eventType); if (!wrappers.isEmpty()) { dispatched = true; for (EventSubscriber wrapper : wrappers) { //事件入队列 enqueueEvent(event, wrapper); } } } finally { subscribersByTypeLock.readLock().unlock(); } }//如果没有订阅者订阅此类消息，则为 DeadEvent if (!dispatched && !(event instanceof DeadEvent)) { post(new DeadEvent(this, event)); } dispatchQueuedEvents(); }
事件隔离
多个EventBus可以隔离事件。
public class AnotherListener { /** * 监听 WorldEvent 类型及其父类型（HelloEvent 和 Object）的事件 */ @Subscribe public void processAnotherWorldEvent(WorldEvent event) { System.out.println("process another world event, no:" + event.getEventNo() + ", name:" + event.getEventName()); }}public class GuavaTest { public static void main(String[] args) { EventBus eventBus = new EventBus(); GeventListener listener = new GeventListener(); eventBus.register(listener); eventBus.post(new HelloEvent("hello")); EventBus anotherEventBus = new EventBus(); AnotherListener anotherListener = new AnotherListener(); anotherEventBus.register(anotherListener); anotherEventBus.post(new WorldEvent("AnotherWorld", 666)); }}
结果是
//eventBus结果与之前相同process hello event, name:hello//anotherEventBus 发布的事件，只被其注册的监听器处理process common event, class:HelloEventprocess another world event, no:666, name:AnotherWorld
适用场景：
- 按照类区分事件 订阅 事件簇 支持自定义event，可以根据event自己写分发器 事件隔离
spring event
spring 新版事件机制也比较简单，看代码。
/** * 继承 ApplicationEvent 的事件 */@Datapublic class HelloEvent extends ApplicationEvent { private String eventName; public HelloEvent(String eventName) { super(eventName); setEventName(eventName); }}/** * 自定义事件 */@Data@NoArgsConstructor@AllArgsConstructorpublic class CustomerEvent { private String name; private Boolean isCustomer;}/** * 监听器类，spring也支持一个类中监听多个事件 */@Component("springListener")public class SpringListener { /** * 监听所有ApplicationEvent类型 及其子类型 的事件 */ @EventListener public void processApplicationEvent(ApplicationEvent event) { System.out.println("process common event, class:" + event.getClass().getSimpleName()); } /** * 监听 HelloEvent类型 事件 */ @EventListener public void processHelloEvent(HelloEvent event) { System.out.println("process helloEvent, name:" + event.getEventName()); } /** * 监听 CustomerEvent 类型事件，但是需要满足condition条件,即isCustomer=true */ @EventListener(condition = "#event.isCustomer") public void processCustomerEvent(CustomerEvent event) { System.out.println("process customer CustomerEvent, name:" + event.getName()); } /** * 监听 CustomerEvent 类型事件，但是需要满足condition条件,即name="miaomiao" */ @EventListener(condition = "#event.getName().equals('miaomiao')") public void processMiaoMiaoEvent(CustomerEvent event) { System.out.println("process miaomiao's CustomerEvent, name:" + event.getName()); } /** * 支持异步处理事件 */ @Async @EventListener public void processAsyncCustomerEvent(CustomerEvent event) { System.out.println("Async process CustomerEvent, name:" + event.getName()); }}//执行类，测试入口@SpringBootApplication@ComponentScan(basePackages = {"com.example.manyao.async"})public class DemoApplication { public static void main(String[] args) throws TException { SpringApplication.run(DemoApplication.class, args); ApplicationContext context = new ClassPathXmlApplicationContext("applicationContext.xml"); String[] names = context.getBeanDefinitionNames(); for(int i=0; i<names.length; i++) { System.out.println(names[i]); } System.out.println("++++++++++"); context.publishEvent(new HelloEvent("helloEvent")); context.publishEvent(new CustomerEvent("customer", true)); context.publishEvent(new CustomerEvent("miaomiao", false)); }}
结果是
//以下是spring上下文event，继承自 ApplicationContextEvent。 用于用户参与上下文生命周期的入口。因为是ApplicationEvent子类型，所以，由processApplicationEvent处理。process common event, class:ContextRefreshedEventprocess common event, class:EmbeddedServletContainerInitializedEventprocess common event, class:ApplicationReadyEventprocess common event, class:ContextRefreshedEvent//以下是上下文中的beanspringListenerorg.springframework.context.annotation.internalConfigurationAnnotationProcessororg.springframework.context.annotation.internalAutowiredAnnotationProcessororg.springframework.context.annotation.internalRequiredAnnotationProcessororg.springframework.context.annotation.internalCommonAnnotationProcessororg.springframework.context.event.internalEventListenerProcessororg.springframework.context.event.internalEventListenerFactory++++++++++//HelloEvent 继承 ApplicationEvent，会被processApplicationEvent处理process common event, class:HelloEvent//监听 HelloEvent类型 的 processHelloEvent 处理process helloEvent, name:helloEvent//非 ApplicationEvent 的事件，则为 PayloadApplicationEventprocess common event, class:PayloadApplicationEvent//isCustomer=true,符合processCustomerEvent处理条件process customer CustomerEvent, name:customer//监听CustomerEvent类型，处理结果Async process CustomerEvent, name:customerprocess common event, class:PayloadApplicationEvent//符合processMiaoMiaoEvent条件process miaomiao's CustomerEvent, name:miaomiaoAsync process CustomerEvent, name:miaomiao//spring 上下文事件process common event, class:ContextClosedEvent
spring 上下文事件
上述例子中的
ContextRefreshedEvent，EmbeddedServletContainerInitializedEvent，ApplicationReadyEvent，ContextRefreshedEvent，ContextClosedEvent 等事件，都是spring上下文事件。可以通过监听这些事件，参与到spring生命周期中去。这种无侵入性交互方式，在做平台服务时，是一种很好的方式。
注册监听器
org.springframework.context.event.EventListenerMethodProcessor#processBean 将所有注解EventListener的方法，存入上下文的applicationListeners中。Listener的封装类为ApplicationListenerMethodAdapter(String beanName, Class<?> targetClass, Method method)。
org.springframework.context.support.AbstractApplicationContext#refresh 中调用 initApplicationEventMulticaster 初始化事件发布管理器applicationEventMulticaster，然后调用registerListeners() 注册监听器。
发布事件
spring 起初只支持 ApplicationEvent类型事件，后来优化之后，支持自定义事件。自定义事件的处理，默认为PayloadApplicationEvent，相当于EventBus的DeadEvent。
//org.springframework.context.support.AbstractApplicationContext#publishEvent(java.lang.Object, org.springframework.core.ResolvableType) protected void publishEvent(Object event, ResolvableType eventType) { Assert.notNull(event, "Event must not be null"); if (logger.isTraceEnabled()) { logger.trace("Publishing event in " + getDisplayName() + ": " + event); } // Decorate event as an ApplicationEvent if necessary ApplicationEvent applicationEvent; if (event instanceof ApplicationEvent) { applicationEvent = (ApplicationEvent) event; } else { //若不是ApplicationEvent类型，则使用PayloadApplicationEvent封装 applicationEvent = new PayloadApplicationEvent<Object>(this, event); if (eventType == null) { eventType = ((PayloadApplicationEvent)applicationEvent).getResolvableType(); } } // Multicast right now if possible - or lazily once the multicaster is initialized if (this.earlyApplicationEvents != null) { this.earlyApplicationEvents.add(applicationEvent); } else {//核心操作，初始化 event getApplicationEventMulticaster().multicastEvent(applicationEvent, eventType); } //调用父类，发布事件 // Publish event via parent context as well... if (this.parent != null) { if (this.parent instanceof AbstractApplicationContext) { ((AbstractApplicationContext) this.parent).publishEvent(event, eventType); } else { this.parent.publishEvent(event); } } }
执行事件
@Override public void multicastEvent(final ApplicationEvent event, ResolvableType eventType) { ResolvableType type = (eventType != null ? eventType : resolveDefaultEventType(event)); //获取事件的监听器集合，并逐个触发执行监听器 for (final ApplicationListener<?> listener : getApplicationListeners(event, type)) { //异步的话，就放在线程池中执行 Executor executor = getTaskExecutor(); if (executor != null) { executor.execute(new Runnable() { @Override public void run() { invokeListener(listener, event); } }); } else { //本线程调用 invokeListener(listener, event); } } }
可以看到，spring的事件机制更复杂，但是功能同样强大。
适用场景：
- 按照类区分事件 订阅 事件簇 支持自定义event 按照condition过滤同类型事件
比较EventBus与Spring Event
使用方式比较
EventBus 任意对象 EventBus EventBus#post 是 注解Subscribe方法 手动注册EventBus#register Spring Event 任意对象 ApplicationEventPublisher ApplicationEventPublisher#publishEvent 支持同步异步 注解EventListener方法 系统注册
使用场景比较
EventBus Class 是 是 否 是 简单 Spring Event Class 是 是 是 否 复杂
更多关于EventBus与Spring Event文章大家可查看下面的相关链接
本文标题: EventBus与Spring Event区别详解(EventBus 事件机制,Spring Event事件机制)
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