JAVA8 分组统计

超、凢脫俗 2022-05-22 00:09 575阅读 0赞

JAVA8使用stream()根据ID对List进行分组统计

Apple类:

/**
     * @version: V1.0
     * @author: fendo
     * @className: Apple
     * @packageName: com.xxx.xxxx.xxxx.xxxx
     * @description: 苹果
     * @data: 2018-06-11 11:15  
     **/
    public class Apple {
    
        /**
         * 主键
         */
        private String id;
    
        /**
         * 名称
         */
        private String name;
    
        /**
         * 价格
         */
        private BigDecimal price;
    
        /**
         * 总数
         */
        private Long count;
    
        /**
         * 类别
         */
        private String type;
    
        public Apple() {
    
        }
    
        public Apple(String id, String name, BigDecimal price, Long count) {
            this.id = id;
            this.name = name;
            this.price = price;
            this.count = count;
        }
    
        public String getId() {
            return id;
        }
    
        public void setId(String id) {
            this.id = id;
        }
    
        public String getName() {
            return name;
        }
    
        public void setName(String name) {
            this.name = name;
        }
    
        public BigDecimal getPrice() {
            return price;
        }
    
        public void setPrice(BigDecimal price) {
            this.price = price;
        }
    
        public Long getCount() {
            return count;
        }
    
        public void setCount(Long count) {
            this.count = count;
        }
    
        public String getType() {
            return type;
        }
    
        public void setType(String type) {
            this.type = type;
        }
    }

测试类:

public static void main(String[] args) {
    
            List<Apple> appleList = Lists.newArrayList();
            Apple apple1 = new Apple();
            apple1.setId("1");
            apple1.setName("fendo1");
            apple1.setCount((long) 10);
            apple1.setType("1");
            apple1.setPrice(new BigDecimal(20));
            appleList.add(apple1);
    
            Apple apple2 = new Apple();
            apple2.setId("2");
            apple2.setName("fendo2");
            apple2.setCount((long) 10);
            apple2.setType("1");
            apple2.setPrice(new BigDecimal(20));
            appleList.add(apple2);
    
            Apple apple6 = new Apple();
            apple6.setId("6");
            apple6.setName("fendo6");
            apple6.setCount((long) 30);
            apple6.setType("1");
            apple6.setPrice(new BigDecimal(20));
            appleList.add(apple6);
    
            Apple apple3 = new Apple();
            apple3.setId("3");
            apple3.setName("fendo3");
            apple3.setCount((long) 10);
            apple3.setType("2");
            apple3.setPrice(new BigDecimal(20));
            appleList.add(apple3);
    
            Apple apple4 = new Apple();
            apple4.setId("4");
            apple4.setName("fendo4");
            apple4.setCount((long) 10);
            apple4.setType("3");
            apple4.setPrice(new BigDecimal(20));
            appleList.add(apple4);
    
            Apple apple5 = new Apple();
            apple5.setId("5");
            apple5.setName("fendo5");
            apple5.setCount((long) 10);
            apple5.setType("4");
            apple5.setPrice(new BigDecimal(20));
            appleList.add(apple5);
    
            //分组
            Map<String,List<Apple>> map = appleList.stream().collect(Collectors.groupingBy(Apple::getType));
            for (Map.Entry<String, List<Apple>> entry : map.entrySet()) {
                System.out.println("分组" + JsonUtil.toJson(entry));
            }
    
            //分组求和
            Map<String, LongSummaryStatistics> collect = appleList.stream().collect(
                    Collectors.groupingBy(Apple::getType,
                            Collectors.summarizingLong(Apple::getCount)));
            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());
            }
    
        }

输出如下:

分组
    {
    	"key": "1",
    	"value": [{
    		"id": "1",
    		"name": "fendo1",
    		"price": 20,
    		"count": 10,
    		"type": "1"
    	}, {
    		"id": "2",
    		"name": "fendo2",
    		"price": 20,
    		"count": 10,
    		"type": "1"
    	}, {
    		"id": "6",
    		"name": "fendo6",
    		"price": 20,
    		"count": 30,
    		"type": "1"
    	}]
    }
    分组
    {
    	"key": "2",
    	"value": [{
    		"id": "3",
    		"name": "fendo3",
    		"price": 20,
    		"count": 10,
    		"type": "2"
    	}]
    }
    分组
    {
    	"key": "3",
    	"value": [{
    		"id": "4",
    		"name": "fendo4",
    		"price": 20,
    		"count": 10,
    		"type": "3"
    	}]
    }
    分组
    {
    	"key": "4",
    	"value": [{
    		"id": "5",
    		"name": "fendo5",
    		"price": 20,
    		"count": 10,
    		"type": "4"
    	}]
    }
    ----------------key----------------1
    求和:50
    求平均16.666666666666668
    求最大:30
    求最小:10
    求总数:3
    ----------------key----------------2
    求和:10
    求平均10.0
    求最大:10
    求最小:10
    求总数:1
    ----------------key----------------3
    求和:10
    求平均10.0
    求最大:10
    求最小:10
    求总数:1
    ----------------key----------------4
    求和:10
    求平均10.0
    求最大:10
    求最小:10
    求总数:1