一、购物车模块复用

主要是判断库存，以及购物车中每个商品状态、价格等包装

//判断库存并返回处理后的结果private CartVo getCartVoLimit(Integer userId){CartVo cartVo = new CartVo();List<Cart> cartList = cartMapper.selectCartByUserId(userId);//用来装配CartProductVoList<CartProductVo> cartProductVoList = Lists.newArrayList();//购物车总价BigDecimal cartTotalPrice = new BigDecimal("0");if (CollectionUtils.isNotEmpty(cartList)){//遍历每一个购物车，计算购物车中的每个产品数量。总价，库存等，用CartProductVo封装for (Cart cartItem : cartList){CartProductVo cartProductVo = new CartProductVo();cartProductVo.setUserId(userId);cartProductVo.setId(cartItem.getId());cartProductVo.setProductId(cartItem.getProductId());//cartProductVo.setQuantity();//cartProductVo.setProductTotalPrice();
Product product = productMapper.selectByPrimaryKey(cartItem.getProductId());if (product != null){cartProductVo.setProductMainImage(product.getMainImage());cartProductVo.setProductSubtitle(product.getSubtitle());cartProductVo.setProductName(product.getName());cartProductVo.setProductPrice(product.getPrice());cartProductVo.setProductStatus(product.getStatus());cartProductVo.setProductStock(product.getStock());//判断库存int buyLimitCount = 0;if (product.getStock() >= cartItem.getQuantity()){//库存充足buyLimitCount = cartItem.getQuantity();cartProductVo.setLimitQuantity(Const.Cart.LIMIT_NUM_SUCCESS);}else {//库存不足buyLimitCount = product.getStock();cartProductVo.setLimitQuantity(Const.Cart.LIMIT_NUM_FAIL);//购物车更新库存Cart updateCart = new Cart();updateCart.setId(cartItem.getId());updateCart.setQuantity(buyLimitCount);cartMapper.updateByPrimaryKeySelective(updateCart);}cartProductVo.setQuantity(buyLimitCount);//总价=产品价格*购物车该产品数量
                    cartProductVo.setProductTotalPrice(BigDecimalUtil.mul(product.getPrice().doubleValue(),cartProductVo.getQuantity()));cartProductVo.setProductChecked(cartItem.getChecked());}if (cartItem.getChecked() == Const.Cart.CHECKED){//如果已经勾选,增加到整个的购物车总价中cartTotalPrice = BigDecimalUtil.add(cartTotalPrice.doubleValue(),cartProductVo.getProductTotalPrice().doubleValue());}cartProductVoList.add(cartProductVo);}}cartVo.setCartTotalPrice(cartTotalPrice);cartVo.setCartProductVoList(cartProductVoList);cartVo.setImageHost(PropertiesUtil.getProperty("ftp.server.http.prefix"));cartVo.setAllChecked(this.isAllChecked(userId));return cartVo;}

二、浮点型商业运算精度丢失问题---使用BigDecimal

package com.mmall.util;import java.math.BigDecimal;/*** @author GenshenWang.nomico* @date 2018/4/17.*/
public class BigDecimalUtil {private BigDecimalUtil(){}public static BigDecimal add(double v1, double v2){BigDecimal b1 = new BigDecimal(Double.toString(v1));BigDecimal b2 = new BigDecimal(Double.toString(v2));return b1.add(b2);}public static BigDecimal sub(double v1, double v2){BigDecimal b1 = new BigDecimal(Double.toString(v1));BigDecimal b2 = new BigDecimal(Double.toString(v2));return b1.subtract(b2);}public static BigDecimal mul(double v1, double v2){BigDecimal b1 = new BigDecimal(Double.toString(v1));BigDecimal b2 = new BigDecimal(Double.toString(v2));return b1.multiply(b2);}public static BigDecimal div(double v1, double v2){BigDecimal b1 = new BigDecimal(Double.toString(v1));BigDecimal b2 = new BigDecimal(Double.toString(v2));//保留两位小数，四舍五入return b1.divide(b2, 2, BigDecimal.ROUND_HALF_UP);}
}

三、IFNULL

  <select id="selectCartProductCount" parameterType="int" resultType="int">select IFNULL(sum(quantity),0) as count from mmall_cart where user_id = #{userId} and</select>