用Stream流方式合并两个list集合（部分对象属性重合）

一、合并出共有部分

package com.xu.demo.test;

import java.util.Arrays;
import java.util.List;
import java.util.stream.Collectors;

public class ListMergeTest1 {

    public static void main(String[] args) {
        List<User> list1 = Arrays.asList(new User(1, "Alice"), new User(2, "Bob"), new User(4, "Ronnie"));
        List<User> list2 = Arrays.asList(new User(2, "Bobby"), new User(3, "Charlie"), new User(5, "Trump"));

        List<User> mergedList = list1.stream()
                .flatMap(user1 -> list2.stream()
                        .filter(user2 -> user1.getId() == user2.getId())
                        .map(user2 -> {
                            User newUser = new User();
                            newUser.setId(user2.getId());
                            newUser.setName(user2.getName());
                            return newUser;
                        })
                )
                .collect(Collectors.toList());

        mergedList.forEach(System.out::println);
    }

}

class User {
    private int id;
    private String name;

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

    // Getter and Setter methods
    public int getId() {
        return id;
    }

    public String getName() {
        return name;
    }

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

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

    public User() {
    }

    @Override
    public String toString() {
        return "User{" +
                "id=" + id +
                ", name='" + name + '\'' +
                '}';
    }
}

运行结果：注意流处理中return的位置

二、合并到某一List（假如保留到第一个List）

package com.xu.demo.test;

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

public class ListMergeTest2 {

    public static void main(String[] args) {

        List<Map<String,Object>> list1 = new ArrayList<>();
        Map<String,Object> data=new HashMap<>();
        data.put("userId","100001");
        data.put("userName","唐僧");
        list1.add(data);
        data=new HashMap<>();
        data.put("userId","100002");
        data.put("userName","八戒");
        list1.add(data);

        List<Map<String,Object>> list2 = new ArrayList<>();
        data=new HashMap<>();
        data.put("userId","100001");
        data.put("gender","男");
        data.put("age",20);
        list2.add(data);
        data=new HashMap<>();
        data.put("userId","100002");
        data.put("gender","雄");
        data.put("age",1000);
        list2.add(data);

        System.out.println(list1);
        System.out.println(list2);

        //使用stream流把list1和list2根据属性userId合并一个list集合
        list1.stream().map(m1 -> {
            list2.stream().filter(m2 -> m1.get("userId").equals(m2.get("userId"))).forEach( m2 -> {
                m1.put("gender", m2.get("gender"));
                m1.put("age", m2.get("age"));
            });
            return m1;
        }).collect(Collectors.toList());

        System.out.println(list1);
        System.out.println(list2);
    }

}

运行结果如下：注意流处理中return的位置