Java将多个list对象根据属性分组后合并成一个新的集合

package com.lqm.collection;

import java.util.*;
import java.util.stream.Collectors;

/**
 * @ProjectName: algorithm
 * @Package: com.*.collection
 * @ClassName: Test4
 * @Author: ***
 * @Description:
 * @Date: 2021/5/19 9:47
 * @Version: 1.0
 */
public class Test4 {

    public static void main(String[] args) {
        List<TimeCount> list1 = new ArrayList<>();
        TimeCount tc11 = new TimeCount("2021-01-06", 1);
        TimeCount tc12 = new TimeCount("2021-01-16", 1);
        list1.add(tc11);
        list1.add(tc12);

        List<TimeCount> list2 = new ArrayList<>();
        TimeCount tc21 = new TimeCount("2021-01-11", 1);
        TimeCount tc22 = new TimeCount("2021-01-14", 1);
        TimeCount tc23 = new TimeCount("2021-01-28", 1);
        TimeCount tc24 = new TimeCount("2021-01-29", 1);
        TimeCount tc25 = new TimeCount("2021-01-30", 1);
        list2.add(tc21);
        list2.add(tc22);
        list2.add(tc23);
        list2.add(tc24);
        list2.add(tc25);

        List<TimeCount> list3 = new ArrayList<>();
        TimeCount tc31 = new TimeCount("2021-01-06", 1);
        TimeCount tc32 = new TimeCount("2021-01-11", 1);
        TimeCount tc33 = new TimeCount("2021-01-28", 1);
        TimeCount tc34 = new TimeCount("2020-01-30", 1);
        list3.add(tc31);
        list3.add(tc32);
        list3.add(tc33);
        list3.add(tc34);


        Map<String, List> map = new HashMap<>();
        for (String s : list1.stream().map(o -> o.getTime()).collect(Collectors.toList())) {
            map.put(s, null);
        }
        for (String s : list2.stream().map(o -> o.getTime()).collect(Collectors.toList())) {
            map.put(s, null);
        }
        for (String s : list3.stream().map(o -> o.getTime()).collect(Collectors.toList())) {
            map.put(s, null);
        }

        for (String s : map.keySet()) {
            List result = new ArrayList();
            List<TimeCount> t1 = list1.stream().filter(o -> o.getTime().equals(s)).collect(Collectors.toList());


            if (t1.size() == 0) {
                result.add(0);
            } else {
                result.add(t1.get(0).getCount());
            }

            List<TimeCount> t2 = list2.stream().filter(o -> o.getTime().equals(s)).collect(Collectors.toList());
            if (t2.size() == 0) {
                result.add(0);
            } else {
                result.add(t2.get(0).getCount());
            }

            List<TimeCount> t3 = list3.stream().filter(o -> o.getTime().equals(s)).collect(Collectors.toList());
            if (t3.size() == 0) {
                result.add(0);
            } else {
                result.add(t3.get(0).getCount());
            }
            map.put(s, result);
        }

　　　　 //按照map中的key进行升序排序
        Map<String, List> sortedMap = map.entrySet().stream()
                .sorted(Map.Entry.comparingByKey())
                .collect(
                        Collectors.toMap(
                                Map.Entry::getKey,
                                Map.Entry::getValue,
                                (oldVal, newVal) -> oldVal,
                                LinkedHashMap::new
                        )
                );

        sortedMap.forEach((k, v) -> System.out.println("key:" + k + "value:" + v));

    }


}

package com.lqm.collection;

/**
 * @ProjectName: algorithm
 * @Package: com.*.collection
 * @ClassName: TimeCount
 * @Author: ***
 * @Description:
 * @Date: 2021/5/19 10:07
 * @Version: 1.0
 */
public class TimeCount {

    private String time;
    private Integer count;

    public TimeCount(String time, Integer count) {
        this.time = time;
        this.count = count;
    }
    public String getTime() {
        return time;
    }

    public void setTime(String time) {
        this.time = time;
    }

    public Integer getCount() {
        return count;
    }

    public void setCount(Integer count) {
        this.count = count;
    }
    @Override
    public String toString() {
        return "TimeCount{" +
                "time='" + time + '\'' +
                ", count=" + count +
                '}';
    }
}

输出结果：

key:2020-01-30value:[0, 0, 1]
key:2021-01-06value:[1, 0, 1]
key:2021-01-11value:[0, 1, 1]
key:2021-01-14value:[0, 1, 0]
key:2021-01-16value:[1, 0, 0]
key:2021-01-28value:[0, 1, 1]
key:2021-01-29value:[0, 1, 0]
key:2021-01-30value:[0, 1, 0]