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分布式锁

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如何使用锁解决超卖问题？

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示例如下所示：

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@Service
@Slf4j
public class OrderService {

    @Resource
    private OrderMapper orderMapper;
    @Resource
    private OrderItemMapper orderItemMapper;
    @Resource
    private ProductMapper productMapper;
    //购买商品id
    private int purchaseProductId = 100100;
    //购买商品数量
    private int purchaseProductNum = 1;
    @Autowired
    private PlatformTransactionManager platformTransactionManager;
    @Autowired
    private TransactionDefinition transactionDefinition;

    private Lock lock = new ReentrantLock();


//    @Transactional(rollbackFor = Exception.class)
    public Integer createOrder() throws Exception{
        Product product = null;

        lock.lock();
        try {
            TransactionStatus transaction1 = platformTransactionManager.getTransaction(transactionDefinition);
            product = productMapper.selectByPrimaryKey(purchaseProductId);
            if (product==null){
                platformTransactionManager.rollback(transaction1);
                throw new Exception("购买商品："+purchaseProductId+"不存在");
            }

            //商品当前库存
            Integer currentCount = product.getCount();
            System.out.println(Thread.currentThread().getName()+"库存数："+currentCount);
            //校验库存
            if (purchaseProductNum > currentCount){
                platformTransactionManager.rollback(transaction1);
                throw
                        new Exception("商品"+purchaseProductId+"仅剩"+currentCount+"件，无法购买");
            }

            productMapper.updateProductCount(purchaseProductNum,"xxx",new Date(),product.getId());
            platformTransactionManager.commit(transaction1);
        }finally {
            lock.unlock();
        }

        TransactionStatus transaction = platformTransactionManager.getTransaction(transactionDefinition);
        Order order = new Order();
        order.setOrderAmount(product.getPrice().multiply(new BigDecimal(purchaseProductNum)));
        order.setOrderStatus(1);//待处理
        order.setReceiverName("xxx");
        order.setReceiverMobile("13311112222");
        order.setCreateTime(new Date());
        order.setCreateUser("xxx");
        order.setUpdateTime(new Date());
        order.setUpdateUser("xxx");
        orderMapper.insertSelective(order);

        OrderItem orderItem = new OrderItem();
        orderItem.setOrderId(order.getId());
        orderItem.setProductId(product.getId());
        orderItem.setPurchasePrice(product.getPrice());
        orderItem.setPurchaseNum(purchaseProductNum);
        orderItem.setCreateUser("xxx");
        orderItem.setCreateTime(new Date());
        orderItem.setUpdateTime(new Date());
        orderItem.setUpdateUser("xxx");
        orderItemMapper.insertSelective(orderItem);
        platformTransactionManager.commit(transaction);
        return order.getId();
    }

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