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开发中遇到的场景描述

• 使用 Echars 做订单金额统计, 横纵坐标分别要用到两组数据. 采用OrderStatisticsVo 返回, 但是要查询的表, 查完后需要对数据进行处理,分别是两个集合
• OrderStatisticsVo

@Data
@Schema(description = "统计结果实体类")
public class OrderStatisticsVo {@Schema(description = "日期数据集合")private List<String> dateList ;@Schema(description = "总金额数据集合")private List<BigDecimal> amountList ;
}

• 但是mapper查询进行封装的实体类属性为

@Data
public class OrderStatistics extends BaseEntity {private Date orderDate;private BigDecimal totalAmount;private Integer totalNum;
}

• 我的mapper

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN" "http://mybatis.org/dtd/mybatis-3-mapper.dtd" >
<mapper namespace="com.chen.manager.mapper.OrderStatisticsMapper"><select id="getOrderStatisticsData" resultType="com.chen.model.entity.order.OrderStatistics">select * from order_statistics<where>is_deleted=0<if test="createTimeBegin!=null and createTimeBegin!=''">and create_time >=#{createTimeBegin}</if><if test="createTimeEnd!=null and createTimeEnd!=''">and create_time &lt;=#{createTimeEnd}</if></where></select>
</mapper>

• services 层的代码,调用mapper去查询 OrderStatistics 实体类
  然后对数据进行封装.

  传统的写法

@Service
public class OrderInfoServiceImpl implements OrderInfoService {@Autowiredprivate OrderStatisticsMapper orderStatisticsMapper;@Overridepublic OrderStatisticsVo getOrderStatisticsData(OrderStatisticsDto orderStatisticsDto) {//返回的vo对象OrderStatisticsVo orderStatisticsVo = new OrderStatisticsVo();List<OrderStatistics> orderStatisticsList=orderStatisticsMapper.getOrderStatisticsData(orderStatisticsDto);//null处理if(CollectionUtil.isEmpty(orderStatisticsList)){throw new MyException(229,"所选时间没有数据");}//    普通的写法ArrayList<String> dataList = new ArrayList<>();ArrayList<BigDecimal> amountList = new ArrayList<>();//  封装 OrderStatisticsVofor (OrderStatistics orderStatistics : orderStatisticsList) {//准备封装数据dataList.add(DateUtil.format(orderStatistics.getOrderDate(),"yyyy-MM-dd"));amountList.add(orderStatistics.getTotalAmount());}//封装返回的数据orderStatisticsVo.setAmountList(amountList);orderStatisticsVo.setDateList(dataList);return orderStatisticsVo;}
}

用stream流中的方法 map 进行处理

演变过程 (看了好理解)

@Service
public class OrderInfoServiceImpl implements OrderInfoService {@Autowiredprivate OrderStatisticsMapper orderStatisticsMapper;@Overridepublic OrderStatisticsVo getOrderStatisticsData(OrderStatisticsDto orderStatisticsDto) {//返回的vo对象OrderStatisticsVo orderStatisticsVo = new OrderStatisticsVo();List<OrderStatistics> orderStatisticsList=orderStatisticsMapper.getOrderStatisticsData(orderStatisticsDto);//null处理if(CollectionUtil.isEmpty(orderStatisticsList)){throw new MyException(229,"所选时间没有数据");}//用 stream流的写发  map用于返回值类型不一样//没有省略代码//        List<Object> dateList = orderStatisticsList.stream().map(new Function<OrderStatistics, Object>() {
//            @Override
//            public Object apply(OrderStatistics orderStatistics) {
//                String date = DateUtil.format(orderStatistics.getOrderDate(), "yyyy-MM-dd");
//                return date;
//            }
//        }).collect(Collectors.toList());//使用箭头函数的形式//        List<String> dataList = orderStatisticsList.stream().map(orderStatistics -> {
//            String date = DateUtil.format(orderStatistics.getOrderDate(), "yyyy-MM-dd");
//
//            return date;
//        }).collect(Collectors.toList());//如果就一行可以 省略 return
//        List<String> dataList = orderStatisticsList.stream().map(orderStatistics ->
//                DateUtil.format(orderStatistics.getOrderDate(), "yyyy-MM-dd")).collect(Collectors.toList());//最终方案直接把结果追加到vo中orderStatisticsVo.setDateList(orderStatisticsList.stream().map(orderStatistics ->DateUtil.format(orderStatistics.getOrderDate(), "yyyy-MM-dd")).collect(Collectors.toList()));//同理处理amount
//        List<BigDecimal> amount = orderStatisticsList.stream().map(orderStatistics -> {
//            BigDecimal totalAmount = orderStatistics.getTotalAmount();
//            return totalAmount;
//        }).collect(Collectors.toList());orderStatisticsVo.setAmountList(orderStatisticsList.stream().map(orderStatistics -> orderStatistics.getTotalAmount()).collect(Collectors.toList()));return orderStatisticsVo;}
}

最简写法

@Service
public class OrderInfoServiceImpl implements OrderInfoService {@Autowiredprivate OrderStatisticsMapper orderStatisticsMapper;@Overridepublic OrderStatisticsVo getOrderStatisticsData(OrderStatisticsDto orderStatisticsDto) {//返回的vo对象OrderStatisticsVo orderStatisticsVo = new OrderStatisticsVo();// 根据时间条件查询List<OrderStatistics> orderStatisticsList=orderStatisticsMapper.getOrderStatisticsData(orderStatisticsDto);//null处理if(CollectionUtil.isEmpty(orderStatisticsList)){throw new MyException(229,"所选时间没有数据");}//封装vo对象//处理dateList 属性orderStatisticsVo.setDateList(orderStatisticsList.stream().map(orderStatistics ->DateUtil.format(orderStatistics.getOrderDate(), "yyyy-MM-dd")).collect(Collectors.toList()));//同理处理amountList 属性orderStatisticsVo.setAmountList(orderStatisticsList.stream().map(orderStatistics -> orderStatistics.getTotalAmount()).collect(Collectors.toList()));return orderStatisticsVo;}
}