核心：避免超卖问题，保证一人一单 

业务逻辑

代码步骤分析

全部代码

@Service
public class VoucherOrderServiceImpl extends ServiceImpl<VoucherOrderMapper, VoucherOrder> implements IVoucherOrderService {

    @Resource
    private ISeckillVoucherService seckillVoucherService;
    @Resource
    private RedisIdWorker redisIdWorker;
    @Resource
    private StringRedisTemplate stringRedisTemplate;
    @Resource
    private RedissonClient redissonClient;

    @Override
    public Result seckillVoucher(Long voucherId) {
        //1 查询优惠券信息
        SeckillVoucher seckillVoucher = seckillVoucherService.getById(voucherId);
        //2 判断秒杀是否开始
        LocalDateTime now = LocalDateTime.now(); //现在时间
        LocalDateTime beginTime = seckillVoucher.getBeginTime(); //开始时间
        LocalDateTime endTime = seckillVoucher.getEndTime(); //结束时间
        if (now.isBefore(beginTime)) {
            return Result.fail("秒杀还未开始");
        }
        //3 判断秒杀是否结束
        if (now.isAfter(endTime)) {
            return Result.fail("秒杀已结束");
        }

        //4 判断库存是否充足
        int stock = (int) seckillVoucher.getStock();
        if (stock == 0 && stock <= 0) {
            return Result.fail("库存不足");
        }

        //确保一人一单 用户ID和代金券ID联合查询
        Long userId = UserHolder.getUser().getId();
        //先获取锁 再提交事务
        //synchronized (userId.toString().intern()) {

        //创建锁对象
        //SimpleRedisLock simpleRedisLock = new SimpleRedisLock("order:" + userId, stringRedisTemplate);
        RLock lock = redissonClient.getLock("lock:order:" + userId);
        //获取锁
        boolean isLock = lock.tryLock();
        //判断是否获取锁成功
        if (!isLock){
            //获取锁失败 返回错误或失败
            return Result.fail("不允许重复下单");
        }
        try {
            //获取事务的代理对象
            IVoucherOrderService proxy = (IVoucherOrderService) AopContext.currentProxy();
            return proxy.creatVoucherOrder(voucherId);
        } finally {
            //释放锁
            lock.unlock();
        }
        //}//事务提交之后在释放锁
    }

    /**
     * 这里对于加锁做出一些解释：如果锁加在整个方法上，那么就会导
     *  致锁的粒度过大，导致每个进程进来都会锁住，所以要控制锁的粒度
     */

    @Transactional
    public Result creatVoucherOrder(Long voucherId) {
        Long userId = UserHolder.getUser().getId();
        Integer count = query().eq("user_id", userId).eq("voucher_id", voucherId).count();
        if (count > 0) {
            return Result.fail("用户已经购买过了");
        }
        //5 扣减库存-
        boolean success = seckillVoucherService.update()
                .setSql("stock = stock -1 ")  //乐观锁
                .eq("voucher_id", voucherId).gt("stock", 0) //判断库存是否大于0: where id = ? and stock > 0
                .update();
        if (!success) {
            return Result.fail("库存不足");
        }
        //6 创建订单
        //6.1 订单ID
        VoucherOrder voucherOrder = new VoucherOrder();
        long orderid = RedisIdWorker.nextId("order");
        voucherOrder.setVoucherId(orderid);
        //6.2 用户ID
        voucherOrder.setUserId(userId);
        //6.3 代金券ID
        voucherOrder.setVoucherId(voucherId);
        save(voucherOrder);
        //7 返回订单id
        return Result.ok(orderid);
    }

}