Java8 Stream针对List先分组再求和、最大值、最小值、平均值等

痛定思痛。 2023-10-10 13:56 40阅读 0赞

**解题思路**：JAVA8使用[stream][]()根据类型对List进行分组统计。

**核心功能代码片段**：

//分组求和
            Map<String, LongSummaryStatistics> collect = list.stream().collect(
                    Collectors.groupingBy(Fruit::getType,
                            Collectors.summarizingLong(Fruit::getTotal)));
            for (Map.Entry<String, LongSummaryStatistics> entry : collect.entrySet()) {
                LongSummaryStatistics longSummaryStatistics = entry.getValue();
                System.out.println("----------------key----------------" + entry.getKey());
                System.out.println("求和:" + longSummaryStatistics.getSum());
                System.out.println("求平均" + longSummaryStatistics.getAverage());
                System.out.println("求最大:" + longSummaryStatistics.getMax());
                System.out.println("求最小:" + longSummaryStatistics.getMin());
                System.out.println("求总数:" + longSummaryStatistics.getCount());
            }

**演示功能代码**：

package com.zzg.test;
    
    import java.math.BigDecimal;
    import java.util.ArrayList;
    import java.util.List;
    import java.util.LongSummaryStatistics;
    import java.util.Map;
    import java.util.stream.Collectors;
    
    import cn.hutool.json.JSONUtil;
    
    /**
     * 基于Java8 分组再统计
     * @author zzg
     *
     */
    public class GroupByStatissticsTest {
    	
    	static List<Fruit> initDate(){
    		List<Fruit> list = new ArrayList<Fruit>();
    		
    		Fruit one = new Fruit();
    		one.setName("苹果一级");
    		one.setSid("1");
    		one.setPrice(new BigDecimal("123456.98").setScale(BigDecimal.ROUND_HALF_UP, 2) );
    		one.setTotal(1100L);
    		one.setType("1");
    		
    		
    		Fruit two = new Fruit();
    		two.setName("苹果二级");
    		two.setSid("2");
    		two.setPrice(new BigDecimal("123546.98").setScale(BigDecimal.ROUND_HALF_UP, 2) );
    		two.setTotal(89L);
    		two.setType("1");
    		
    		Fruit three = new Fruit();
    		three.setName("苹果三级");
    		three.setSid("3");
    		three.setPrice(new BigDecimal("987.98").setScale(BigDecimal.ROUND_HALF_UP, 2) );
    		three.setTotal(1039L);
    		three.setType("1");
    		
    		Fruit four = new Fruit();
    		four.setName("梨子一级");
    		four.setSid("4");
    		four.setPrice(new BigDecimal("97.98").setScale(BigDecimal.ROUND_HALF_UP, 2) );
    		four.setTotal(39L);
    		four.setType("2");
    		
    		Fruit five = new Fruit();
    		five.setName("梨子二级");
    		five.setSid("5");
    		five.setPrice(new BigDecimal("970.98").setScale(BigDecimal.ROUND_HALF_UP, 2) );
    		five.setTotal(399L);
    		five.setType("2");
    		
    		Fruit six = new Fruit();
    		six.setName("西瓜一级");
    		six.setSid("6");
    		six.setPrice(new BigDecimal("1970.98").setScale(BigDecimal.ROUND_HALF_UP, 2) );
    		six.setTotal(2399L);
    		six.setType("3");
    		
    		list.add(one);
    		list.add(two);
    		list.add(three);
    		list.add(four);
    		list.add(five);
    		list.add(six);
    		return list;
    	}
    
    	public static void main(String[] args) {
    		// TODO Auto-generated method stub
    		List<Fruit> list = initDate();
    		
    		  //分组
            Map<String,List<Fruit>> map = list.stream().collect(Collectors.groupingBy(Fruit::getType));
            for (Map.Entry<String, List<Fruit>> entry : map.entrySet()) {
                System.out.println("分组" + JSONUtil.toJsonStr(entry));
            }
            
          //分组求和
            Map<String, LongSummaryStatistics> collect = list.stream().collect(
                    Collectors.groupingBy(Fruit::getType,
                            Collectors.summarizingLong(Fruit::getTotal)));
            for (Map.Entry<String, LongSummaryStatistics> entry : collect.entrySet()) {
                LongSummaryStatistics longSummaryStatistics = entry.getValue();
                System.out.println("----------------key----------------" + entry.getKey());
                System.out.println("求和:" + longSummaryStatistics.getSum());
                System.out.println("求平均" + longSummaryStatistics.getAverage());
                System.out.println("求最大:" + longSummaryStatistics.getMax());
                System.out.println("求最小:" + longSummaryStatistics.getMin());
                System.out.println("求总数:" + longSummaryStatistics.getCount());
            }
    
    
    	}
    	
    	static class Fruit{
    		private String sid;
    		private String name;
    		private String type;
    		private Long total;
    		private BigDecimal price;
    		public String getSid() {
    			return sid;
    		}
    		public void setSid(String sid) {
    			this.sid = sid;
    		}
    		public String getName() {
    			return name;
    		}
    		public void setName(String name) {
    			this.name = name;
    		}
    		public String getType() {
    			return type;
    		}
    		public void setType(String type) {
    			this.type = type;
    		}
    		public Long getTotal() {
    			return total;
    		}
    		public void setTotal(Long total) {
    			this.total = total;
    		}
    		public BigDecimal getPrice() {
    			return price;
    		}
    		public void setPrice(BigDecimal price) {
    			this.price = price;
    		}
    		
    		
    		
    	}
    
    }

**效果截图**：

![watermark_type_d3F5LXplbmhlaQ_shadow_50_text_Q1NETiBA5Zyo5aWL5paX55qE5aSn6YGT_size_20_color_FFFFFF_t_70_g_se_x_16][]

[stream]: https://so.csdn.net/so/search?q=stream&spm=1001.2101.3001.7020
[watermark_type_d3F5LXplbmhlaQ_shadow_50_text_Q1NETiBA5Zyo5aWL5paX55qE5aSn6YGT_size_20_color_FFFFFF_t_70_g_se_x_16]: https://img-blog.csdnimg.cn/a7f4cbcb09c545b3a56374730fc342c9.png?x-oss-process=image/watermark,type_d3F5LXplbmhlaQ,shadow_50,text_Q1NETiBA5Zyo5aWL5paX55qE5aSn6YGT,size_20,color_FFFFFF,t_70,g_se,x_16