java8 集合 多字段 分组 统计个数

1.user实体

package com.demo.dto;

public class User {
    private Integer id;

    private String userName;

    private String password;

    private Integer age;
    
    private long c;
    

    public User() {
        super();
        // TODO Auto-generated constructor stub
    }

    public User(Integer id, String userName, String password, Integer age) {
        super();
        this.id = id;
        this.userName = userName;
        this.password = password;
        this.age = age;
    }

    public Integer getId() {
        return id;
    }

    public void setId(Integer id) {
        this.id = id;
    }

    public String getUserName() {
        return userName;
    }

    public void setUserName(String userName) {
        this.userName = userName == null ? null : userName.trim();
    }

    public String getPassword() {
        return password;
    }

    public void setPassword(String password) {
        this.password = password == null ? null : password.trim();
    }

    public Integer getAge() {
        return age;
    }

    public void setAge(Integer age) {
        this.age = age;
    }

    public long getC() {
        return c;
    }

    public void setC(long l) {
        this.c = l;
    }

    @Override
    public String toString() {
        return "User [id=" + id + ", userName=" + userName + ", password=" + password + ", age=" + age + ", c=" + c
                + "]";
    }
    public static void main(String[] args) {
        
        User u1=new User(1, "aa", "aap", 23);
        User u2=new User(2, "aa", "aap", 23);
        User u3=new User(3, "bb", "aap", 23);
        User u4=new User(4, "cc", "aap", 23);
        User u5=new User(5, "cc", "aap", 23);
        User u6=new User(6, "cc", "aap", 23);
        User u7=new User(7, "aa", "aap", 24);
        List<User> list=new ArrayList<User>();
        list.add(u1);list.add(u2);list.add(u7);list.add(u3);list.add(u4);list.add(u5);list.add(u6);
//原有list(根据第二个字段:userName和第四个字段:age 统计重复的记录数)
//jdk8的方法统计个数:
Map<String, Map<Integer, Long>> map = list.stream().collect(Collectors.groupingBy(User::getUserName,Collectors.groupingBy(User::getAge,Collectors.counting())));
//jdk8以下:
        Map<String,Map<Integer,Long>> map=new HashMap<String,Map<Integer,Long>>();
        for (User user1 : list) {
                Map<Integer, Long> value=new HashMap<Integer,Long>();
                long count=0;
                if(map.containsKey(user1.getUserName())){
                    continue;
                }
                for(int i=0;i<list.size();i++){
                    if(user1.getUserName().equals(list.get(i).getUserName())&&user1.getAge()==list.get(i).getAge()){
                        count+=1;
                        value.put(user1.getAge(),count);
                        map.put(user1.getUserName(), value);
                    }else if(user1.getUserName().equals(list.get(i).getUserName())&&user1.getAge()!=list.get(i).getAge()){
                        value.put(list.get(i).getAge(),Long.valueOf(1));
                        map.put(user1.getUserName(), value);
                    }
                }
        }
        map.forEach((k, v) -> {
            System.out.println(k+">>>>"+v);
        });
        List<User> list2=new ArrayList<User>();
        list.forEach(user ->{
            map.forEach((k, v) -> {
                if(k==user.getUserName()){
                    Long remove = v.remove(user.getAge());
                    user.setC(null==remove?0:remove);
                }
            });
            list2.add(user);
        });
        //遍历最后想要的结果(User中c为统计后的个数，方便前台遍历集合时单元格合并行)
        list2.forEach(u ->{
            System.out.println(u);
        });
        
    }
}

备注：运行结果如下

cc>>>>{23=3}
bb>>>>{23=1}
aa>>>>{23=2, 24=1}
User [id=1, userName=aa, password=aap, age=23, c=2]
User [id=2, userName=aa, password=aap, age=23, c=0]
User [id=7, userName=aa, password=aap, age=24, c=1]
User [id=3, userName=bb, password=aap, age=23, c=1]
User [id=4, userName=cc, password=aap, age=23, c=3]
User [id=5, userName=cc, password=aap, age=23, c=0]
User [id=6, userName=cc, password=aap, age=23, c=0]

此处是为了实现如下效果：