EventBus监听模式实例

目录

先定义一个注解

自定义一个EventBus

EventBus启动配置

定义事件类型实体, 和对应的监听操作

发布事件

小结

---

先定义一个注解

/**
 * eventbus开启注解，只有开启了该注解的类的方法才可用Subscribe注解监听event事件
 * @author zsd
 */
@Documented
@Retention(RetentionPolicy.RUNTIME)
@Target({ElementType.TYPE})
@Component
public @interface EventHandler {

}

自定义一个EventBus

@Slf4j
public class EventBus implements InitializingBean {

    private org.greenrobot.eventbus.EventBus publisher;

    private TransactionTemplate transactionTemplate;

    private PlatformTransactionManager platformTransactionManager;

    public EventBus(org.greenrobot.eventbus.EventBus publisher, PlatformTransactionManager platformTransactionManager) {
        this.platformTransactionManager = platformTransactionManager;
        this.publisher = publisher;
    }

    public void register(Object bean) {
        publisher.register(bean);
    }

    public void unregister(Object bean){
        publisher.unregister(bean);
    }

    public void publishAfterTransaction(Serializable message) {
        if (TransactionSynchronizationManager.isSynchronizationActive()
                && transactionTemplate != null) {
            TransactionSynchronizationManager.registerSynchronization(
                    new TransactionSynchronizationAdapter() {
                        @Override
                        public void afterCompletion(int status) {
                            if (status == TransactionSynchronization.STATUS_COMMITTED) {
                                transactionTemplate.execute(
                                        status1 -> {
                                            EventBus.this.publish(message);
                                            return null;
                                        });
                            }
                        }
                    });
        } else {
            EventBus.this.publish(message);
        }
    }

    public void publish(Serializable message) {
        if(log.isDebugEnabled()) {
            log.debug("发送事件:{}", message);
        }
        publisher.post(message);
    }


    @Override
    public void afterPropertiesSet(){
        if (platformTransactionManager != null) {
            DefaultTransactionDefinition defaultTransactionDefinition =
                    new DefaultTransactionDefinition();
            defaultTransactionDefinition.setPropagationBehavior(
                    TransactionDefinition.PROPAGATION_REQUIRES_NEW);
            transactionTemplate =
                    new TransactionTemplate(platformTransactionManager, defaultTransactionDefinition);
        } else {
            log.warn("spring事务管理器不存在，publishAfterTransactionCommitted方法不会绑定到事务中!");
        }
    }

}

EventBus启动配置

@Configuration
@Setter
@Slf4j
public class EventBusAutoConfiguration implements ApplicationContextAware {

    private ApplicationContext applicationContext;

    @Resource
    private ExecutorService executorService;

    @Autowired(required = false)
    private PlatformTransactionManager platformTransactionManager;

    @Override
    public void setApplicationContext(ApplicationContext applicationContext) throws BeansException {
        this.applicationContext = applicationContext;
    }

    @Bean
    public EventBus eventBus(){
        EventBusBuilder eventBusBuilder = org.greenrobot.eventbus.EventBus.builder().executorService(executorService);
        org.greenrobot.eventbus.EventBus eBus = eventBusBuilder.build();
        EventBus eventBus = new EventBus(eBus, platformTransactionManager);
        eventBus.afterPropertiesSet();
        return eventBus;
    }


    @Configuration
    @AutoConfigureAfter(EventBusAutoConfiguration.class)
    public static class EventHandlerConfig {
        @Autowired
        private EventBus eventBus;

        @PostConstruct
        public void afterPropertiesSet(){
            Map<String, Object> beansWithAnnotation =
                    SpringApplicationContextHolder.getApplicationContext().getBeansWithAnnotation(EventHandler.class);
            for (Object o : beansWithAnnotation.values()) {
                eventBus.register(o);
                log.info("注册事件处理器:{}", o.getClass().getName());
            }
        }

        @PreDestroy
        public void destroy(){
            Map<String, Object> beansWithAnnotation =
                    SpringApplicationContextHolder.getApplicationContext().getBeansWithAnnotation(EventHandler.class);
            for (Object o : beansWithAnnotation.values()) {
                eventBus.unregister(o);
                log.info("销毁事件处理器:{}", o.getClass().getName());
            }
        }
    }
}

---

接下来是如何使用

定义事件类型实体, 和对应的监听操作

@EventHandler
@Slf4j
public class OrderEventListener {

    @Subscribe
    public void onOrderCreate(OrderCreateEvent event) {
        log.info("onOrderCreate : {}", event);
    }

    @Subscribe
    public void onOrderUpdate(OrderUpdateEvent event) {
        log.info("onOrderUpdate : {}", event);
    }

    @Subscribe(threadMode = ThreadMode.ASYNC)
    public void onOrderDelete(OrderDeleteEvent event) {
        log.info("onOrderDelete : {}", event);
    }

    @Getter
    @AllArgsConstructor
    public static class OrderCreateEvent implements Serializable {

        private static final long serialVersionUID = -7018526633366219070L;

        public String name;

    }

    @Getter
    @AllArgsConstructor
    public static class OrderDeleteEvent implements Serializable {

        private static final long serialVersionUID = -1514539831268656303L;

    }

    @Getter
    @AllArgsConstructor
    public static class OrderUpdateEvent implements Serializable {

        private static final long serialVersionUID = 3668604429118137965L;

    }

}

发布事件

@Service
public class MyService {
    @Autowired
    private EventBus eventBus;

    public void getNames(){
        OrderEventListener.OrderCreateEvent event = new OrderEventListener.OrderCreateEvent("zsd");
        eventBus.publish(event);
    }
}

小结

一种内存中的发布订阅模式,或者监听器模式, 重在解耦