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 {
    
    
    @Autowired
    private OrderStatisticsMapper orderStatisticsMapper;

    @Override
    public 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 OrderStatisticsVo
        for (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 {
    
    
    @Autowired
    private OrderStatisticsMapper orderStatisticsMapper;

    @Override
    public 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 {
    
    
    @Autowired
    private OrderStatisticsMapper orderStatisticsMapper;

    @Override
    public 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;
    }
}