苍穹外卖的购物车userId为null，解决方法

一、在WebMvcConfiguration文件里要注意的两个点   
1、private JwtTokenUserInterceptor jwtTokenUserInterceptor;这段代码别写错。

2、 .addPathPatterns("/user/**") 之前在视频里面有一条弹幕说前面user不要加"/",虽然可以暂时让小程序显示出页面内容，但在购物车这里暴露出问题了，拦截器拦截不到/user前缀的接口了，所以还是要加上的。

    @Autowired
    private JwtTokenAdminInterceptor jwtTokenAdminInterceptor;
    @Autowired
    private JwtTokenUserInterceptor jwtTokenUserInterceptor;

    /**
     * 注册自定义拦截器
     *
     * @param registry
     */
    protected void addInterceptors(InterceptorRegistry registry) {
        log.info("开始注册自定义拦截器...");
        registry.addInterceptor(jwtTokenAdminInterceptor)
                .addPathPatterns("/admin/**")
                .excludePathPatterns("/admin/employee/login");
        registry.addInterceptor(jwtTokenUserInterceptor)
                .addPathPatterns("/user/**")
                .excludePathPatterns("/user/user/login")
                .excludePathPatterns("/user/shop/status");
    }

二、JwtTokenUserInterceptor文件里要注意的

1.   Long userId = Long.valueOf(claims.get(JwtClaimsConstant.USER_ID).toString());其中的JwtClaimsConstant.USER_ID这段代码。因为代码是从JwtTokenAdminInterceptor复制过来的，这段代码JwtClaimsConstant.EMP_ID没注意改成USER_ID就导致user_id为null

public class JwtTokenUserInterceptor implements HandlerInterceptor {

    @Autowired
    private JwtProperties jwtProperties;

    /**
     * 校验jwt
     *
     * @param request
     * @param response
     * @param handler
     * @return
     * @throws Exception
     */
    public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception {
        //判断当前拦截到的是Controller的方法还是其他资源
        if (!(handler instanceof HandlerMethod)) {
            //当前拦截到的不是动态方法，直接放行
            return true;
        }
        //1、从请求头中获取令牌
        String token = request.getHeader(jwtProperties.getUserTokenName());

        //2、校验令牌
        try {
            log.info("jwt校验:{}", token);
            Claims claims = JwtUtil.parseJWT(jwtProperties.getUserSecretKey(), token);
            Long userId = Long.valueOf(claims.get(JwtClaimsConstant.USER_ID).toString());
            log.info("当前用户id：", userId);
            BaseContext.setCurrentId(userId);
            //3、通过，放行
            return true;
        } catch (Exception ex) {
            //4、不通过，响应401状态码
            response.setStatus(401);
            return false;
        }
    }
}

三、ShoppingCartServiceImpl文件

1、注意是 shoppingCart.setUserId(userId);不是setId

    public void addShoppingCart(ShoppingCartDTO shoppingCartDTO) {
        //判断当前加入购物车的商品是否已存在
        ShoppingCart shoppingCart = new ShoppingCart();
        BeanUtils.copyProperties(shoppingCartDTO,shoppingCart);
        Long userId = BaseContext.getCurrentId();
        shoppingCart.setUserId(userId);
        List<ShoppingCart> list = shoppingCartMapper.list(shoppingCart);
        //如果存在，则增加数量
        if(list != null && list.size() > 0){
            ShoppingCart cart = list.get(0);
            cart.setNumber(cart.getNumber() + 1);
            shoppingCartMapper.updateNumberById(cart);
        }else{
            //如果不存在，需要插入一条购物车数据
            Long dishId = shoppingCartDTO.getDishId();
            if(dishId != null){
                Dish dish = dishMapper.getById(dishId);
                shoppingCart.setName(dish.getName());
                shoppingCart.setImage(dish.getImage());
                shoppingCart.setAmount(dish.getPrice());

                shoppingCart.setNumber(1);
                shoppingCart.setCreateTime(LocalDateTime.now());
            }else{
                Long setmealId = shoppingCartDTO.getSetmealId();
                Setmeal setmeal = setmealMapper.getById(setmealId);
                shoppingCart.setName(setmeal.getName());
                shoppingCart.setImage(setmeal.getImage());
                shoppingCart.setAmount(setmeal.getPrice());
            }
            shoppingCart.setNumber(1);
            shoppingCart.setCreateTime(LocalDateTime.now());
            shoppingCartMapper.insert(shoppingCart);
        }
        //则添加到购物车，数量默认为1
    }