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 methodspublic 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() {}@Overridepublic 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