【设计模式】基于责任链模式的参数校验

介绍

责任链模式（Chain of Responsibility Pattern）是一种行为设计模式，可以通过将一系列处理器按顺序链接起来，使得每个处理器都有机会处理请求，从而实现请求的传递和处理。

此处我们用一个创建订单的例子 在创建订单前进行各种的前置校验

接口定义

public interface OrderCreateValidator {
    /**
     * 设置下一个校验器
     *
     * @param nextValidator
     */
    public void setNext(OrderCreateValidator nextValidator);

    /**
     * 返回下一个校验器
     *
     * @return
     */
    public OrderCreateValidator getNext();

    /**
     * 校验
     *
     * @param request
     * @throws OrderException 订单异常
     */
    public void validate(OrderCreateRequest request) throws OrderException;
}

根实现类

public abstract class BaseOrderCreateValidator implements OrderCreateValidator {

    protected OrderCreateValidator nextValidator;

    @Override
    public void setNext(OrderCreateValidator nextValidator) {
        this.nextValidator = nextValidator;
    }

    @Override
    public OrderCreateValidator getNext() {
        return nextValidator;
    }

    /**
     * 校验
     *
     * @param request
     * @throws Exception
     */
    @Override
    public void validate(OrderCreateRequest request) throws OrderException {
        doValidate(request);

        if (nextValidator != null) {
            nextValidator.validate(request);
        }
    }

    /**
     * 校验方法的具体实现
     *
     * @param request
     * @throws OrderException
     */
    protected abstract void doValidate(OrderCreateRequest request) throws OrderException;
}

具体校验器的实现

用户校验器

public class UserValidator extends BaseOrderCreateValidator {

    private UserFacadeService userFacadeService;

    @Override
    public void doValidate(OrderCreateRequest request) throws OrderException {
        String buyerId = request.getBuyerId();
        UserQueryRequest userQueryRequest = new UserQueryRequest(Long.valueOf(buyerId));
        UserQueryResponse<UserInfo> userQueryResponse = userFacadeService.query(userQueryRequest);
        if (userQueryResponse.getSuccess() && userQueryResponse.getData() != null) {
            UserInfo userInfo = userQueryResponse.getData();
            if (userInfo.getUserRole() != null && !userInfo.getUserRole().equals(UserRole.CUSTOMER)) {
                throw new OrderException(BUYER_IS_PLATFORM_USER);
            }
            //判断买家状态
            if (userInfo.getState() != null && !userInfo.getState().equals(UserStateEnum.ACTIVE.name())) {
                throw new OrderException(BUYER_STATUS_ABNORMAL);
            }
            //判断买家状态
            if (userInfo.getState() != null && !userInfo.getCertification()) {
                throw new OrderException(BUYER_NOT_AUTH);
            }
        }
    }

    public UserValidator(UserFacadeService userFacadeService) {
        this.userFacadeService = userFacadeService;
    }

    public UserValidator() {
    }
}

商品校验器

public class GoodsValidator extends BaseOrderCreateValidator {

    private GoodsFacadeService goodsFacadeService;

    @Override
    protected void doValidate(OrderCreateRequest request) throws OrderException {
        BaseGoodsVO baseGoodsVO = goodsFacadeService.getGoods(request.getGoodsId(), request.getGoodsType());

        // 如果商品不是可售状态，则返回失败
        // PS：可售状态为什么要包含SOLD_OUT呢？因为商品查询的接口中去查询了 Redis 的最新库存，而 Redis 的库存在下单时可能已经扣减过刚好为0了，所以这里要包含 SOLD_OUT
        if (baseGoodsVO.getState() != GoodsState.SELLING && baseGoodsVO.getState() != GoodsState.SOLD_OUT) {
            throw new OrderException(GOODS_NOT_AVAILABLE);
        }

        if (baseGoodsVO.getPrice().compareTo(request.getItemPrice()) != 0) {
            throw new OrderException(GOODS_PRICE_CHANGED);
        }
    }

    public GoodsValidator(GoodsFacadeService goodsFacadeService) {
        this.goodsFacadeService = goodsFacadeService;
    }

    public GoodsValidator() {
    }
}

预定校验器

public class GoodsBookValidator extends BaseOrderCreateValidator {

    private GoodsFacadeService goodsFacadeService;

    @Override
    protected void doValidate(OrderCreateRequest request) throws OrderException {
        BaseGoodsVO baseGoodsVO = goodsFacadeService.getGoods(request.getGoodsId(), request.getGoodsType());
        if(baseGoodsVO.canBook()){
            Boolean hasBooked = goodsFacadeService.isGoodsBooked(request.getGoodsId(), request.getGoodsType(), request.getBuyerId());

            if (!hasBooked) {
                throw new OrderException(GOODS_NOT_BOOKED);
            }
        }
    }

    public GoodsBookValidator(GoodsFacadeService goodsFacadeService) {
        this.goodsFacadeService = goodsFacadeService;
    }

    public GoodsBookValidator() {
    }
}

库存校验器

public class GoodsBookValidator extends BaseOrderCreateValidator {

    private GoodsFacadeService goodsFacadeService;

    @Override
    protected void doValidate(OrderCreateRequest request) throws OrderException {
        BaseGoodsVO baseGoodsVO = goodsFacadeService.getGoods(request.getGoodsId(), request.getGoodsType());
        if(baseGoodsVO.canBook()){
            Boolean hasBooked = goodsFacadeService.isGoodsBooked(request.getGoodsId(), request.getGoodsType(), request.getBuyerId());

            if (!hasBooked) {
                throw new OrderException(GOODS_NOT_BOOKED);
            }
        }
    }

    public GoodsBookValidator(GoodsFacadeService goodsFacadeService) {
        this.goodsFacadeService = goodsFacadeService;
    }

    public GoodsBookValidator() {
    }
}

责任链的编排

实现配置类

@Configuration
public class OrderCreateValidatorConfig {

    @Autowired
    private GoodsValidator goodsValidator;

    @Autowired
    private UserValidator userValidator;

    @Autowired
    private GoodsBookValidator goodsBookValidator;

    @Bean
    public OrderCreateValidator orderValidatorChain() {
        userValidator.setNext(goodsValidator);
        goodsValidator.setNext(goodsBookValidator);
        return userValidator;
    }
}

使用

 //责任链模式 订单创建前的参数校验
 orderPreValidatorChain.validate(orderCreateRequest);