校园外卖系统源码开发实战：商户端、骑手端、后台端三端架构拆解

前端层：
- 商户端（Vue/UniApp）
- 骑手端（UniApp/Flutter）
- 管理后台（Vue + Element）

网关层：
- Nginx + API Gateway

服务层：
- 用户服务
- 订单服务
- 商品服务
- 调度服务
- 支付服务

数据层：
- MySQL
- Redis
- MQ（RabbitMQ/Kafka）

// 下单时预扣库存
public boolean deductStock(Long productId, Integer quantity) {
    String key = "stock:" + productId;
    Long stock = redisTemplate.opsForValue().decrement(key, quantity);

    if (stock < 0) {
        redisTemplate.opsForValue().increment(key, quantity);
        return false;
    }

    // 发送MQ异步落库
    mqSender.sendStockMessage(productId, quantity);
    return true;
}

@RabbitListener(queues = "stock.queue")
public void updateStock(StockMessage msg) {
    productMapper.updateStock(msg.getProductId(), msg.getQuantity());
}

public Rider dispatch(Order order) {
    List<Rider> riders = riderService.getOnlineRiders();

    return riders.stream()
        .sorted(Comparator.comparing(r ->
            distance(r.getLat(), r.getLng(),
                     order.getShopLat(), order.getShopLng())))
        .findFirst()
        .orElse(null);
}

public double distance(double lat1, double lng1,
                       double lat2, double lng2) {
    double radLat1 = Math.toRadians(lat1);
    double radLat2 = Math.toRadians(lat2);
    double a = radLat1 - radLat2;
    double b = Math.toRadians(lng1 - lng2);

    double s = 2 * Math.asin(Math.sqrt(
        Math.pow(Math.sin(a/2),2) +
        Math.cos(radLat1)*Math.cos(radLat2)
        *Math.pow(Math.sin(b/2),2)));

    return s * 6378137;
}

public enum OrderStatus {
    CREATED,
    PAID,
    MERCHANT_ACCEPTED,
    COOKING,
    WAITING_RIDER,
    DELIVERING,
    COMPLETED,
    CANCELED
}

public void changeStatus(Order order, OrderStatus targetStatus) {
    if(!validTransition(order.getStatus(), targetStatus)){
        throw new RuntimeException("非法状态流转");
    }
    order.setStatus(targetStatus);
    orderMapper.update(order);
}

public BigDecimal calculateSettlement(Order order) {
    BigDecimal commissionRate = new BigDecimal("0.10");
    BigDecimal commission = order.getAmount().multiply(commissionRate);

    return order.getAmount().subtract(commission);
}

@Scheduled(cron = "0 0 2 * * ?")
public void generateSettlement() {
    settlementService.generateWeekly();
}

@OnMessage
public void onMessage(String message, Session session) {
    session.getBasicRemote().sendText("新订单提醒");
}