基于Spring的发布订阅模式 EventListener

基于Spring的发布订阅模式

在我们使用spring开发应用时，经常会碰到要去解耦合一些依赖调用，比如我们在做代码的发布流程中，需要去通知相关的测试，开发人员关注发布中的错误信息。而且通知这个操作又不希望强耦合在主业务流程中，这个时候我们很容易就想到了观察者设计模式，而spring恰好提供了事件-监听机制，让我们看一下他们是具体怎么实现的吧。

事件-监听机制：

1. 首先是一种对象间的一对多的关系；最简单的如交通信号灯，信号灯是目标（一方），行人注视着信号灯（多方）；
2. 当目标发送改变（发布），观察者（订阅者）就可以接收到改变；
3. 观察者如何处理（如行人如何走，是快走/慢走/不走，目标不会管的），目标无需干涉；所以就松散耦合了它们之间的关系。

Spring提供的事件驱动模型/观察者抽象

其实整个模型就有三个角色，事件，目标（发布者），监听者，我们看一下spring中如何实现这三者

事件：

具体代表者是：ApplicationEvent：

1、 我们可以看到spring中ApplicationEvent该抽象类继承自JDK的EventObject。JDK要求所有事件将继承它，并通过source得到事件源。

package org.springframework.context;

import java.util.EventObject;

/**
 * Class to be extended by all application events. Abstract as it
 * doesn't make sense for generic events to be published directly.
 *
 * @author Rod Johnson
 * @author Juergen Hoeller
 */
public abstract class ApplicationEvent extends EventObject {

	/** use serialVersionUID from Spring 1.2 for interoperability */
	private static final long serialVersionUID = 7099057708183571937L;

	/** System time when the event happened */
	private final long timestamp;

	/**
	 * Create a new ApplicationEvent.
	 * @param source the object on which the event initially occurred (never {@code null})
	 */
	public ApplicationEvent(Object source) {
		super(source);
		this.timestamp = System.currentTimeMillis();
	}

	/**
	 * Return the system time in milliseconds when the event happened.
	 */
	public final long getTimestamp() {
		return this.timestamp;
	}

}

　　

目标(发布者)

具体代表者是具体代表者是：ApplicationEventPublisher及ApplicationEventMulticaster。ApplicationContext该接口继承了ApplicationEventPublisher，并在AbstractApplicationContext实现了具体代码，实际执行是委托给ApplicationEventMulticaster（可以认为是多播）：

ApplicationContext继承自ApplicationEventPublisher

public interface ApplicationContext extends EnvironmentCapable, ListableBeanFactory, HierarchicalBeanFactory,
		MessageSource, ApplicationEventPublisher, ResourcePatternResolver {
}

ApplicationEventPublisher定义了publishEvent方法

public interface ApplicationEventPublisher {

    /**
     * Notify all <strong>matching</strong> listeners registered with this
     * application of an application event. Events may be framework events
     * (such as RequestHandledEvent) or application-specific events.
     * @param event the event to publish
     * @see org.springframework.web.context.support.RequestHandledEvent
     */
    void publishEvent(ApplicationEvent event);

    /**
     * Notify all <strong>matching</strong> listeners registered with this
     * application of an event.
     * <p>If the specified {@code event} is not an {@link ApplicationEvent},
     * it is wrapped in a {@link PayloadApplicationEvent}.
     * @param event the event to publish
     * @since 4.2
     * @see PayloadApplicationEvent
     */
    void publishEvent(Object event);

}

在AbstractApplicationContext实现了具体代码,实际执行是委托给ApplicationEventMulticaster（可以认为是多播）

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 {
            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 {
            getApplicationEventMulticaster().multicastEvent(applicationEvent, eventType);
        }

        // 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);
            }
        }
    }

ApplicationContext自动到本地容器里找一个ApplicationEventMulticaster实现，如果没有自己new一个SimpleApplicationEventMulticaster。

public void multicastEvent(final ApplicationEvent event, ResolvableType eventType) {
        ResolvableType type = (eventType != null ? eventType : resolveDefaultEventType(event));
        for (final ApplicationListener<?> listener : getApplicationListeners(event, type)) {
            Executor executor = getTaskExecutor();
            if (executor != null) {
                executor.execute(new Runnable() {
                    @Override
                    public void run() {
                        invokeListener(listener, event);
                    }
                });
            }
            else {
                invokeListener(listener, event);
            }
        }
    }

大家可以看到如果给它一个executor（java.util.concurrent.Executor），它就可以异步支持发布事件了。

所以我们发送事件只需要通过ApplicationContext.publishEvent即可

监听器

具体代表者是：ApplicationListener

1、其继承自JDK的EventListener

package org.springframework.context;

import java.util.EventListener;

/**
 * Interface to be implemented by application event listeners.
 * Based on the standard {@code java.util.EventListener} interface
 * for the Observer design pattern.
 *
 * <p>As of Spring 3.0, an ApplicationListener can generically declare the event type
 * that it is interested in. When registered with a Spring ApplicationContext, events
 * will be filtered accordingly, with the listener getting invoked for matching event
 * objects only.
 *
 * @author Rod Johnson
 * @author Juergen Hoeller
 * @param <E> the specific ApplicationEvent subclass to listen to
 * @see org.springframework.context.event.ApplicationEventMulticaster
 */
public interface ApplicationListener<E extends ApplicationEvent> extends EventListener {

	/**
	 * Handle an application event.
	 * @param event the event to respond to
	 */
	void onApplicationEvent(E event);

}

　　

我们在spring中自己实现的demo:

1.定义事件

@Data
public class OrderCreateEvent extends ApplicationEvent {

    private String tradeOrderNo;
    private Long userId;

    public OrderCreateEvent(Object source, String tradeOrderNo, Long userId) {
        super(source);
        this.tradeOrderNo = tradeOrderNo;
        this.userId = userId;
    }

}

　　

2.实现目标(发布者)

public interface OrderPublisher {

    default void publish(ApplicationEvent event) {
        ApplicationContext context = SpringBeanUtil.getContext();
        context.publishEvent(event);
    }

}

　　

3.实现监听器

方式一

@Component
@Slf4j
public class OrderEventHandler {

    private static final Gson gson = new GsonBuilder().setDateFormat("yyyy-MM-dd HH:mm:ss").create();

    @Async
    @EventListener
    public void createHandle(OrderCreateEvent event) {
        RedisKey redisKey = new RedisKey("order", "create", event.getTradeOrderNo());
        if (redisTemplate.hasKey(redisKey.toString())) {
            return;
        }
        Order order = (Order) event.getSource();
        //调用 HSF 接口创建订单落 ES
        try {
            Boolean syncResult = orderSyncEsServiceProxy.createOrder(order);
            if (!syncResult) {
                log.error("同步订单 tradeOrderNo:[{}]，创建订单失败", order.getTradeOrderNo());
            }
        } catch (Throwable e) {
            log.error("同步订单 tradeOrderNo:[{}]，创建订单异常:", order.getTradeOrderNo(), e);
        }

        String messageId = mqProductConfig.sendMessage(
                mqPropertiesConfig.getGroupNameMap().get(MqGroupConstant.GroupType.GID_CREATE_ORDER),
                MqGroupConstant.Tag.CREATE_ORDER_TAG,
                event.getTradeOrderNo(), 60 * 30L);

        redisTemplate.opsForValue().set(redisKey.toString(), gson.toJson(event), 60 * 60 * 24, TimeUnit.SECONDS);

        // 锁定用户权益
        benefitServiceProxy.lockCouponBenefit(order);

        // 用户信息
        UserInfoDTO userInfoDTO =
                userServiceProxy.queryUserInfo(order.getUserId(), order.getSubOrders().get(0).getAddressId(),
                        order.getTradeChannel(), null);

        // 创建订单埋点
        youShuTrackService.track(TrackFactory.createOrderFactory(order, userInfoDTO), YouShuApiEnum.ORDER_ADD);
        log.error("[{}] OrderEventHandler.createHandle.event , messageId [{}] ", event.getTradeOrderNo(), messageId);
    }

    @Async
    @EventListener
    public void paidHandle(OrderPaidEvent event) {
        RedisKey redisKey = new RedisKey("order", "paid", event.getTradeOrderNo());
        if (redisTemplate.hasKey(redisKey.toString())) {
            return;
        }
        redisTemplate.opsForValue().set(redisKey.toString(), gson.toJson(event), 60 * 60 * 24, TimeUnit.SECONDS);

        // 拼团付款成功后 开团或者加团接口
        Order order = (Order) event.getSource();
        if (BusinessTypeEnum.AID_GROUP_ORDER.getCode().equals(order.getBizType()) ||
                BusinessTypeEnum.COMMUNITY_GROUP_ORDER.getCode().equals(order.getBizType())) {
            aidGroupServiceProxy.createAndJoinGroup(order);
        }

        // 使用用户权益
        benefitServiceProxy.useCouponBenefit(order);
    }

    @Async
    @EventListener
    public void confirmHandle(OrderConfirmEvent event) {
        RedisKey redisKey = new RedisKey("order", "confirm", event.getTradeOrderNo());
        if (redisTemplate.hasKey(redisKey.toString())) {
            return;
        }

        String messageId = mqProductConfig.sendMessage(
                mqPropertiesConfig.getGroupNameMap().get(MqGroupConstant.GroupType.GID_CONFIRM_ORDER),
                MqGroupConstant.Tag.CONFIRM_ORDER_TAG + evn,
                gson.toJson(event.getSource()), 0L);

        Map<String, String> eventMap = Maps.newHashMap();
        eventMap.put("event", gson.toJson(event));
        eventMap.put("source", gson.toJson(event.getSource()));
        eventMap.put("messageId", messageId);
        redisTemplate.opsForHash().putAll(redisKey.toString(), eventMap);
        redisTemplate.expire(redisKey.toString(), 60 * 60 * 24, TimeUnit.SECONDS);

        Order source = (Order) event.getSource();
        source.getSubOrders().forEach(subOrder -> {
            itemLimitHelper.addItemLimitNum(subOrder.getUserId(), subOrder.getBizItemId(),
                    subOrder.getBuyAmount().intValue(), subOrder.getTradeChannel(), source.getBizType());
        });

        // 订单 - 确单，埋点
        youShuTrackService.track(TrackFactory.updateOrderFactory(event.getTradeOrderNo(), TrackOrderStatusEnum.UN_TRANSPORT), YouShuApiEnum.ORDER_UPDATE);
        log.error("[{}]OrderEventHandler.confirmHandle success , messageId=[{}]", event.getTradeOrderNo(), messageId);
    }

    @Async
    @EventListener
    public void refundHandle(OrderRefundEvent event) {

        RefundOrderDTO refundOrderDTO = event.getRefundOrderDTO();
        log.info("[{}] OrderEventHandler.refundHandle", event.getTradeOrderNo());
        log.info("refundOrderDTO is{}", JSON.toJSONString(refundOrderDTO));
        RedisKey redisKey = new RedisKey("order", "refund", event.getTradeOrderNo());
        if (refundOrderDTO != null) {
            redisKey = new RedisKey("order", "refund", event.getTradeOrderNo(),
                    CollectionUtils.isEmpty(refundOrderDTO.getTradeSubOrderIdList()) ? "" :
                            Joiner.on(",").join(refundOrderDTO.getTradeSubOrderIdList()));
        }

        if (redisTemplate.hasKey(redisKey.toString())) {
            return;
        }

        RefundMqDTO refundMqDTO = new RefundMqDTO();
        refundMqDTO.setTradeOrderNo(event.getTradeOrderNo());
        if (refundOrderDTO != null) {
            refundMqDTO.setRefundFee(refundOrderDTO.getRefundFee());
            refundMqDTO.setSubOrderId(refundOrderDTO.getTradeSubOrderId());
            refundMqDTO.setSubOrderIdList(refundOrderDTO.getTradeSubOrderIdList());
        }

        String messageId = mqProductConfig.sendMessage(
                mqPropertiesConfig.getGroupNameMap().get(MqGroupConstant.GroupType.GID_REFUND_PAYMENT),
                MqGroupConstant.Tag.REFUND_PAYMENT,
                GsonUtils.gson().toJson(refundMqDTO), 0L);

        redisTemplate.opsForValue().set(redisKey.toString(), messageId, 3, TimeUnit.DAYS);

        Order order = (Order) event.getSource();

        //退款根据
        benefitServiceProxy.returnCouponBenefit(order);

        if (Objects.nonNull(refundOrderDTO) && Objects.nonNull(refundOrderDTO.getBenefitRefundFee())
                && refundOrderDTO.getBenefitRefundFee() > 0) {
            benefitServiceProxy.returnBenefitDiscountFee(order.getUserId(), order.getTradeOrderNo(),
                    refundOrderDTO.getTradeSubOrderIdList(), refundOrderDTO.getBenefitRefundFee());
        }
        //库存回退
        if (TradeChannelEnum.WECHAT_SUBSCRIPTION.getCode().equals(order.getTradeChannel())) {
            Date startDeliveryDate = order.getSubOrders().get(0).getSubOrderLine().getStartDeliveryDate();
            saleStockOptProxy.returnStock(SaleStockOptProxy.groupBizItemByOrder(order), startDeliveryDate);
        }

        //全部退款进行调用es更新兼容拼团退款
        if (Objects.isNull(refundOrderDTO) || CollectionUtils.isEmpty(refundOrderDTO.getTradeSubOrderIdList())) {
            orderSyncEsServiceProxy.changeOrderStatus(order.getTradeOrderNo(), OrderPayStatusEnum.CLOSED);
        }
        // 退款埋点
        youShuTrackService.track(TrackFactory.returnOrderFactory(order), YouShuApiEnum.ORDER_RETURN);
        log.error("[{}]OrderEventHandler.refundHandle success , messageId=[{}]", event.getTradeOrderNo(), messageId);
    }

    @Async
    @EventListener
    public void cancelHandle(OrderCancelEvent event) {
        log.info("[{}] OrderEventHandler.cancelHandle", event.getTradeOrderNo());
        RedisKey redisKey = new RedisKey("order", "cancel", event.getTradeOrderNo());
        if (redisTemplate.hasKey(redisKey.toString())) {
            return;
        }

        redisTemplate.opsForValue().set(redisKey.toString(), System.currentTimeMillis() + "", 3, TimeUnit.DAYS);

        Order order = (Order) event.getSource();

        //权益解锁
        benefitServiceProxy.unLockCouponBenefit(order);

        //库存回退
        if (TradeChannelEnum.WECHAT_SUBSCRIPTION.getCode().equals(order.getTradeChannel())) {
            log.info("startReturnStock : {}", JSON.toJSONString(SaleStockOptProxy.groupBizItemByOrder(order)));
            Date startDeliveryDate = order.getSubOrders().get(0).getSubOrderLine().getStartDeliveryDate();
            saleStockOptProxy.returnStock(SaleStockOptProxy.groupBizItemByOrder(order), startDeliveryDate);
        }

        String freezerNum = AttributesUtils.getAttrByKey(order.getAttributes(), "appoint_freezer");
        String freezerBoxNum = AttributesUtils.getAttrByKey(order.getAttributes(), "appoint_freezer_box");

        freezerOperationProxy.unlockBox(freezerNum, freezerBoxNum);

        // 接龙活动套餐库存
        if (BusinessTypeEnum.JIE_LONG_ORDER.getCode().equals(order.getBizType())) {
            Long storeId = order.getSubOrders().get(0).getStoreId();
            String comboId = AttributesUtils.getAttrByKey(order.getAttributes(), "combo_id");
            if (comboId == null) {
                log.error("Order content error {}", JSON.toJSONString(order));
                throw new BusinessException(OrderErrorCode.ITEM_NOT_EXISTS);
            }

            comboStoreServiceProxy.returnStock(Long.parseLong(comboId), storeId);
        }

        orderSyncEsServiceProxy.changeOrderStatus(order.getTradeOrderNo(), OrderPayStatusEnum.PAID_OUTTIME);

        // 订单 - 取消，埋点
        youShuTrackService.track(TrackFactory.updateOrderFactory(event.getTradeOrderNo(), TrackOrderStatusEnum.CANCEL_UN_PAY), YouShuApiEnum.ORDER_UPDATE);
        log.info("[{}]OrderEventHandler.cancelHandle success", event.getTradeOrderNo());
    }

}

好了，通过这3步，我们就可以在spring中愉快的实现事件-监听机制了。在我们需要发送事件时，只要调用 EventService的发送方法即可

@Slf4j
@Builder
@Data
@AllArgsConstructor
@NoArgsConstructor
public class Order extends BaseDO implements OrderPublisher {
    private Long orderId;
    private String bizType;
    private String tradeOrderNo;
    private Long totalFee;
    private Long actualPaidFee;
    private Long discountFee;
    private Long refundFee;
    private Date payTime;
    private Date refundTime;
    private Integer status;
    private Long userId;
    private String tradeChannel;
    private String attributes;
    private Long deliveryFee;
    private List<SubOrder> subOrders;
    private List<Promotion> promotions;

    public void create() {
        this.publish(new OrderCreateEvent(this, this.tradeOrderNo, this.userId));
    }

    public void confirm() {
        this.publish(new OrderConfirmEvent(this, this.tradeOrderNo, this.userId));
    }

    public void paid() {
        this.publish(new OrderPaidEvent(this, this.tradeOrderNo, this.userId));
    }

    public void refund(RefundOrderDTO subOrderId) {
        this.publish(new OrderRefundEvent(this, this.tradeOrderNo, this.userId,subOrderId));
    }

    public void canceled() {
        this.publish(new OrderCancelEvent(this, this.tradeOrderNo, this.userId));
    }

    public void finishPaid() {
        if (this.status == OrderPayStatusEnum.PAID_DONE.getValue() || this.status == OrderPayStatusEnum.PAID_DONE_SHIPPED.getValue()) {
            return;
        }
        if (this.status != OrderPayStatusEnum.UN_PAID.getValue()) {
            throw new BusinessException(OrderErrorCode.ORDER_STATUS_IS_ERROR);
        }
        this.status = OrderPayStatusEnum.PAID_DONE.getValue();
        this.payTime = new Date();
    }

    public void confirmOrder() {
        if (this.status == OrderPayStatusEnum.PAID_DONE_SHIPPED.getValue()) {
            return;
        }
        if (this.status == OrderPayStatusEnum.CLOSED.getValue()) {
            return;
        }
        if (this.status != OrderPayStatusEnum.PAID_DONE.getValue()) {
            throw new BusinessException(OrderErrorCode.ORDER_STATUS_IS_ERROR);
        }
        this.status = OrderPayStatusEnum.PAID_DONE_SHIPPED.getValue();
        subOrders.forEach(subOrder -> {
            if (subOrder.getStatus() != SubOrderStatusEnum.INIT.getValue()) {
                throw new BusinessException(OrderErrorCode.ORDER_STATUS_IS_ERROR);
            }
            subOrder.setStatus(SubOrderStatusEnum.WAIT.getValue());
        });
    }

    public void cancel() {
        if (this.status != OrderPayStatusEnum.UN_PAID.getValue()) {
            return;
        }
        if (this.status == OrderPayStatusEnum.PAID_OUTTIME.getValue()) {
            return;
        }
        this.status = OrderPayStatusEnum.PAID_OUTTIME.getValue();
    }

    public void complete(Long subOrderId) {
        subOrders.stream().filter(e -> e.getSubOrderId().equals(subOrderId)).forEach(subOrder -> {
            subOrder.setStatus(SubOrderStatusEnum.END.getValue());
        });

        if (subOrders.stream().allMatch(subOrder ->
                SubOrderStatusEnum.END.getValue().equals(subOrder.getStatus()) ||
                        SubOrderStatusEnum.TXP_CLOSE.getValue().equals(subOrder.getStatus())
        )) {
            this.status = OrderPayStatusEnum.SUCCESS.getValue();
        }
    }

    public void refundOrder(Long refundFee, Date refundDate) {
        if (this.status == OrderPayStatusEnum.UN_PAID.getValue()) {
            throw new BusinessException(OrderErrorCode.ORDER_STATUS_IS_ERROR);
        }
        if (this.status == OrderPayStatusEnum.CLOSED.getValue()) {
            throw new BusinessException(RefundErrorCode.ORDER_IS_REFUND);
        }
        refundOrder(refundFee, refundDate, null, null);
    }

}

　　

使用@EventListener还支持SPEL表达式

@EventListener(condition = "#jkRecordConfirmEvent.jkRecordConfirmEventDTO.cwConfirmAndReturnFlag")
@Async("asyncListenerExecutor")

　　

我们可以看到在监听器中，实现的方法使用了@Async注解。在spring3提供了@Aync注解来完成异步调用。我们可以使用这个新特性来完成异步调用。在实际项目中，我们一般也是把这两者结合来使用的，特别是监听事件是一件耗时过程时，这种方式降低了代码的耦合性，非常好用。