新建表

create table if not exists order_info (
    id varchar(32) not null default '',
    user_id int not null default 0,
    item_id int not null default 0,
    item_price double(10, 2) not null default 0,
    amount int not null default 0,
    order_price double(10, 2) default 0,
    primary key (id)
);

create table if not exists sequence_info (
    name varchar(64) not null default '',
    current_value int not null default 0,
    step int not null default 1,
    primary key (name)
);
insert into sequence_info (name, current_value, step) values ('order_info', 1, 1);

新增 OrderModel

public class OrderModel {
    private String id;
    private Integer userId;
    private Integer itemId;
    private BigDecimal itemPrice;
    private Integer amount;
    private BigDecimal orderPrice;

    public String getId() {
        return id;
    }

    public void setId(String id) {
        this.id = id;
    }

    public Integer getUserId() {
        return userId;
    }

    public void setUserId(Integer userId) {
        this.userId = userId;
    }

    public Integer getItemId() {
        return itemId;
    }

    public void setItemId(Integer itemId) {
        this.itemId = itemId;
    }

    public BigDecimal getItemPrice() {
        return itemPrice;
    }

    public void setItemPrice(BigDecimal itemPrice) {
        this.itemPrice = itemPrice;
    }

    public Integer getAmount() {
        return amount;
    }

    public void setAmount(Integer amount) {
        this.amount = amount;
    }

    public BigDecimal getOrderPrice() {
        return orderPrice;
    }

    public void setOrderPrice(BigDecimal orderPrice) {
        this.orderPrice = orderPrice;
    }
}

新增 ItemService

public interface ItemService {

    ItemModel createItem(ItemModel itemModel) throws BusinessException;

    List<ItemModel> listItem();

    ItemModel getItemById(Integer id);

    boolean decreaseStock(Integer itemId, Integer amount);

    void increaseSales(Integer itemId, Integer amount) throws BusinessException;
}

新增 ItemServiceImpl

@Service
public class ItemServiceImpl implements ItemService {

    @Autowired
    private ValidatorImpl validator;

    @Autowired
    private ItemDOMapper itemDOMapper;

    @Autowired
    private ItemStockDOMapper itemStockDOMapper;

    @Override
    @Transactional
    public ItemModel createItem(ItemModel itemModel) throws BusinessException {

        ValidationResult result = validator.validate(itemModel);
        if(result.isHasErrors()){
            throw new BusinessException(EmBusinessError.PARAMETER_VALIDATION_ERROR, result.getErrMsg());
        }

        ItemDO itemDO = convertFromModel(itemModel);
        itemDOMapper.insertSelective(itemDO);

        itemModel.setId(itemDO.getId());

        ItemStockDO itemStockDO = convertItemStockFromModel(itemModel);
        itemStockDOMapper.insertSelective(itemStockDO);

        return getItemById(itemModel.getId());
    }

    @Override
    public List<ItemModel> listItem() {
        List<ItemDO> itemDOList = itemDOMapper.listItem();

        List<ItemModel> itemModelList = itemDOList.stream().map(itemDO -> {
            ItemStockDO itemStockDO = itemStockDOMapper.selectByItemId(itemDO.getId());
            ItemModel itemModel = convertFromDataObject(itemDO, itemStockDO);
            return itemModel;
        }).collect(Collectors.toList());

        return itemModelList;
    }

    @Override
    public ItemModel getItemById(Integer id) {
        ItemDO itemDO = itemDOMapper.selectByPrimaryKey(id);
        if(itemDO == null){
            return null;
        }

        ItemStockDO itemStockDO = itemStockDOMapper.selectByItemId(itemDO.getId());

        ItemModel itemModel = convertFromDataObject(itemDO, itemStockDO);

        return itemModel;
    }

    private ItemDO convertFromModel(ItemModel itemModel){
        if(itemModel == null){
            return null;
        }

        ItemDO itemDO = new ItemDO();
        BeanUtils.copyProperties(itemModel, itemDO);

        itemDO.setPrice(itemModel.getPrice().doubleValue());

        return itemDO;
    }

    private ItemStockDO convertItemStockFromModel(ItemModel itemModel){
        if(itemModel == null){
            return null;
        }

        ItemStockDO itemStockDO = new ItemStockDO();
        itemStockDO.setItemId(itemModel.getId());
        itemStockDO.setStock(itemModel.getStock());

        return itemStockDO;
    }

    private ItemModel convertFromDataObject(ItemDO itemDO, ItemStockDO itemStockDO){
        if(itemDO == null){
            return null;
        }

        ItemModel itemModel = new ItemModel();
        BeanUtils.copyProperties(itemDO, itemModel);

        itemModel.setPrice(new BigDecimal(itemDO.getPrice()));

        itemModel.setStock(itemStockDO.getStock());

        return itemModel;
    }

    @Override
    @Transactional
    public boolean decreaseStock(Integer itemId, Integer amount) {

        int affectedRow = itemStockDOMapper.decreaseStock(itemId, amount);

        return affectedRow > 0;
    }

    @Override
    @Transactional
    public void increaseSales(Integer itemId, Integer amount) throws BusinessException {
        itemDOMapper.increaseSales(itemId, amount);
    }
}

新增 OrderController

@Controller("order")
@RequestMapping("/order")
@CrossOrigin(allowCredentials = "true", allowedHeaders = "*")
public class OrderController extends BaseController {

    @Autowired
    private OrderService orderService;
    @Autowired
    private HttpServletRequest httpServletRequest;

    @RequestMapping(value = "/createorder", method = {RequestMethod.POST}, consumes = {CONTENT_TYPE_FORMED})
    @ResponseBody
    public CommonReturnType createOrder(@RequestParam(name="itemId") Integer itemId,
                                        @RequestParam(name="amount") Integer amount)
            throws BusinessException {

        Boolean isLogin = (Boolean)httpServletRequest.getSession().getAttribute("LOGIN");
        if(isLogin == null || !isLogin.booleanValue()){
            throw new BusinessException(EmBusinessError.USER_NOT_LOGIN);
        }

        UserModel userModel = (UserModel)httpServletRequest.getSession().getAttribute("LOGIN_USER");

        OrderModel orderModel = orderService.createOrder(userModel.getId(), itemId, amount);

        return CommonReturnType.create(null);
    }
}

源码：spring-boot-seckill