Java8新特性 List集合根据map的key相同去重

package com.ndsoft.single;

import com.alibaba.fastjson.JSON;

import java.util.ArrayList;
import java.util.List;
import java.util.Map;
import java.util.stream.Collectors;

public class JavaList8 {
    public static void main(String[] args) {
        User user1 = new User(1, "张三", "no1", 27);
        User user2 = new User(2, "李四", "no2", 15);
        User user3 = new User(3, "王五", "no1", 24);
        User user4 = new User(4, "赵六", "no3", 15);
        User user5 = new User(5, "李七", "no1", 29);
        User user6 = new User(6, "钱八", "no3", 18);
        User user7 = new User(7, "孙九", "no1", 25);
        User user8 = new User(8, "周八", "no2", 19);
        User user9 = new User(8, "周八", "no2", 19);

        List<User> list = new ArrayList<>();
        list.add(user1);
        list.add(user2);
        list.add(user3);
        list.add(user4);
        list.add(user5);
        list.add(user6);
        list.add(user7);
        list.add(user8);
        list.add(user9);

        // List转map：把list里面的元素拿出来作为map的value，自己定义key
        // a->a, (k1,k2)->k1: 如果有重复的key就返回第一个
        Map<Integer, User> map1 = list.stream().collect(Collectors.toMap(User::getId, a -> a, (k1, k2) -> k1));
        // map 转 list
        List<User> collect = map1.entrySet().stream().map(e -> e.getValue()).collect(Collectors.toList());
        collect.stream().map((p) -> {
            String user = JSON.toJSONString(p);
            return user;
        }).distinct().forEach(System.out::println);

    }
}
class User {
    private int id;
    private String name;
    private String classNo;
    private int age;
    public User() {

    }
    public User(int id, String name, String classNo, int age) {
        this.id = id;
        this.name = name;
        this.classNo = classNo;
        this.age = age;
    }

    public int getId() {
        return id;
    }

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

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public String getClassNo() {
        return classNo;
    }

    public void setClassNo(String classNo) {
        this.classNo = classNo;
    }

    public int getAge() {
        return age;
    }

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