Redis抢单预热的实现示例

<dependencies>
        <!-- 放在最前面依赖，依据依赖的最短路径原则，
             将不在使用spring-data中的slf4j，否则
             会引发冲突-->
        <dependency>
            <groupId>ch.qos.logback</groupId>
            <artifactId>logback-classic</artifactId>
            <version>1.3.8</version>
        </dependency>

        <!-- spring data框架，提供了对redis的整合支持，
             内部支持lettuce以及Jedis客户端-->
        <dependency>
            <groupId>org.springframework.data</groupId>
            <artifactId>spring-data-redis</artifactId>
            <version>2.5.6</version>
        </dependency>

        <dependency>
            <groupId>javax.servlet</groupId>
            <artifactId>javax.servlet-api</artifactId>
            <version>4.0.1</version>
            <scope>provided</scope>
        </dependency>

        <dependency>
            <groupId>org.springframework</groupId>
            <artifactId>spring-webmvc</artifactId>
            <version>5.3.29</version>
        </dependency>

        <dependency>
            <groupId>org.springframework</groupId>
            <artifactId>spring-jdbc</artifactId>
            <version>5.3.29</version>
        </dependency>

        <dependency>
            <groupId>org.springframework</groupId>
            <artifactId>spring-tx</artifactId>
            <version>5.3.29</version>
        </dependency>

        <dependency>
            <groupId>com.alibaba</groupId>
            <artifactId>druid</artifactId>
            <version>1.2.3</version>
        </dependency>

        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <version>8.0.32</version>
        </dependency>

        <dependency>
            <groupId>io.lettuce</groupId>
            <artifactId>lettuce-core</artifactId>
            <version>6.2.2.RELEASE</version>
        </dependency>

        <dependency>
            <groupId>org.projectlombok</groupId>
            <artifactId>lombok</artifactId>
            <version>1.18.12</version>
        </dependency>

        <dependency>
            <groupId>junit</groupId>
            <artifactId>junit</artifactId>
            <version>4.12</version>
        </dependency>

        <dependency>
            <groupId>com.fasterxml.jackson.core</groupId>
            <artifactId>jackson-databind</artifactId>
            <version>2.11.2</version>
        </dependency>

        <dependency>
            <groupId>org.mybatis</groupId>
            <artifactId>mybatis</artifactId>
            <version>3.5.6</version>
        </dependency>

        <dependency>
            <groupId>org.mybatis</groupId>
            <artifactId>mybatis-spring</artifactId>
            <version>2.0.6</version>
        </dependency>
    </dependencies>

public interface GoodsDao {

    /**
     * 查询参与活动的商品
     * @return
     */
    List<Goods> listProduct();

    /**
     * 减库存
     * @param id
     * @return
     */
    void decrStock(int id);
}

public interface OrderService {
    /**
     * 下单
     * @param id
     */
    void placeOrder(int id);
}

public interface GoodsService {

    /**
     * 扣减库存
     * @param id
     */
    void decrStock(int id);
}

@Service
@Slf4j
@RequiredArgsConstructor
@Transactional(rollbackFor = RuntimeException.class)
public class GoodsServiceImpl implements GoodsService {

    private final GoodsDao goodsDao;

    private final RedisTemplate<String, Object> redisTemplate;

    /**
     * 缓存预热
     */
    @PostConstruct
    public void initProductCache() {
        goodsDao.listProduct().forEach(goods -> {
            //将商品数量加入redis缓存
            String key = GoodsEnum.PREFIX.value() + goods.getId();
            redisTemplate.opsForValue().set(key, goods.getStock(), Duration.ofMinutes(60));
        });
    }

    @Override
    public void decrStock(int id) {
        goodsDao.decrStock(id);
    }
}

@Service
@Slf4j
@RequiredArgsConstructor
@Transactional
public class OrderServiceImpl implements OrderService {

    private final RedisTemplate<String, Object> redisTemplate;

    private final OrderDao orderDao;

    private final GoodsDao goodsDao;

    /**
     * 下单
     * @param id
     */
    @Override
    public void placeOrder(int id) {
        //扣减库存
        decrCacheStock(id);
        //生成订单
        createOrder(id);
        //同步数据库的库存
        goodsDao.decrStock(id);
    }

    /**
     * 在缓存中扣减库存
     * @param id
     */
    private void decrCacheStock(int id) {
        //扣减库存(原子减)，并返回剩余库存量
        long stock = redisTemplate.opsForValue().decrement(GoodsEnum.PREFIX.value() + id);
        //如果redis中库存为0，则抛出异常告诉用户已经售罄
        if(stock < 0) {
            //在并发时redis扣减后的库存为负数，因此要将redis自增回来
            redisTemplate.opsForValue().increment(GoodsEnum.PREFIX.value() + id);
            throw new OrderException(ErrorMessageEnum.SELL_OUT);
        }
    }

    /**
     * 生成订单
     * @param gid
     */
    private Order createOrder(int gid) {
        try {
            Order order = new Order();
            //用户ID
            order.setUserId(1);
            //商品ID
            order.setGoodsId(gid);
            //0表示未支付
            order.setStatus(0);
            orderDao.save(order);
            return order;
        } catch (Exception e) {
            log.error(e.getMessage(), e);
            throw new RuntimeException(e);
        }
    }
}

@RestController
@RequiredArgsConstructor
public class OrderController extends BaseController{

    private final OrderService orderService;

    @PostMapping("/seckill")
    public ResultVO placeOrder(Integer gid) {
        orderService.placeOrder(2);
        return success();
    }
}