实战与原理：如何基于RocketMQ实现分布式事务？

@Override
public String payment(String orderSn) {
    // todo 集成支付宝支付
    // 支付流水号
    String outOrderNo = IdUtils.get32UUID();
    TradeOrder tradeOrder = Optional.ofNullable(tradeOrderService.getByOrderSn(orderSn)).orElseThrow(() -> new BusinessException("订单编号不存在"));

    // 如果订单处于待支付状态
    if (Objects.equals(tradeOrder.getStatus(), OrderStatusEnum.WAITING_PAYMENT.getStatus())) {

        OrderPaidEvent orderPaidEvent = new OrderPaidEvent(orderSn, outOrderNo);

        TransactionSendResult sendResult = enhanceTemplate.sendTransaction("TRADE-ORDER", "ORDER-PAID");

        if (SendStatus.SEND_OK == sendResult.getSendStatus() && sendResult.getLocalTransactionState() == LocalTransactionState.COMMIT_MESSAGE) {
            return tradeOrder.getOrderSn();
        } else {
            throw new BusinessException("支付失败...");
        }
    } else {
        throw new BusinessException("订单已支付，请勿重复提交...");
    }
}

@Component
@Slf4j
public class OrderPaidTransactionConsumer implements RocketMQLocalTransactionListener {
    
    @Resource
    private TransactionTemplate transactionTemplate;
    @Resource
    private TradeOrderService tradeOrderService;
    
   
  /**
     * 执行本地事务
     * 将订单状态修改成已支付
     */
    @Override
    public RocketMQLocalTransactionState executeLocalTransaction(Message message, Object o) {
        
        final OrderPaidEvent orderPaidEvent = JsonUtils.byte2Obj((byte[]) message.getPayload(), OrderPaidEvent.class);
        try {
            // 放到同一个本地事务中
            this.transactionTemplate.executeWithoutResult(status -> {
                String orderSn = orderPaidEvent.getOrderSn();
                // 修改成待发货
                tradeOrderService.changeOrderStatus(orderSn, OrderStatusEnum.AWAITING_SHIPMENT);
            });
            return RocketMQLocalTransactionState.COMMIT;
        } catch (Exception e) {
            log.error("修改订单状态失败", e);
            // ROLLBACK 则回滚消息，rocketmq将废弃这条消息
            return RocketMQLocalTransactionState.ROLLBACK;
            // 如果是UNKNOWN, 则触发回查
        }

    }

    /**
     * 检查本地事务执行状态
     * 消息回查时，对于正在进行中的事务不要返回Rollback或Commit结果，应继续保持Unknown的状态。
     */
    @Override
    public RocketMQLocalTransactionState checkLocalTransaction(Message message) {
        final OrderPaidEvent orderPaidEvent = JsonUtils.byte2Obj((byte[]) message.getPayload(), OrderPaidEvent.class);

        String orderSn = orderPaidEvent.getOrderSn();
        TradeOrder tradeOrder = tradeOrderService.getByOrderSn(orderSn);
        // 如果已经修改成待发货说明本地事务执行成功，此时消费端可以直接消费
        if (Objects.equals(tradeOrder.getStatus(), OrderStatusEnum.AWAITING_SHIPMENT.getStatus())) {
            return RocketMQLocalTransactionState.COMMIT;
        } else {
            // 这里查不到的时候返回 UNKNOWN在于，有可能事务还没有提交，回查就开始了
            return RocketMQLocalTransactionState.UNKNOWN;
        }
    }
}

@Component
@Slf4j
@RocketMQMessageListener(consumerGroup = "dailymart_inventory_group", topic = "TRADE-ORDER", selectorExpression = "ORDER-PAID")
public class InventoryDeductionConsumer extends EnhanceMessageHandler<OrderPaidEvent> implements RocketMQListener<OrderPaidEvent> {
    
    @Resource
    private InventoryDomainService inventoryDomainService;
    
    @Override
    public void onMessage(OrderPaidEvent orderPaidEvent) {
        super.dispatchMessage(orderPaidEvent);
    }
    
    @Override
    protected void handleMessage(OrderPaidEvent orderPaidEvent) throws Exception {
        // 执行库存扣减逻辑
        String orderSn = orderPaidEvent.getOrderSn();
        inventoryDomainService.deductionInventory(orderSn);
    }
}