java取出list中某几个属性组成一个新集合的几种方式

package org.springblade.test;
 
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import java.util.stream.Collectors;
 
public class Test {
 
    @org.junit.jupiter.api.Test
    public void aaa() {
        User user1 = new User("张三", 10, 1);
        User user2 = new User("李四 ", 11, 1);
        User user3 = new User("王五", 12, 0);
        List<User> users = new ArrayList<>();
        users.add(user1);
        users.add(user2);
        users.add(user3);
        //我这里都转为了List<Map<String, Object>>数组,也可以转换为一个新的实体类(自行创建)
        //使用forEach循环转化
        List<Map<String, Object>> infosFromForEach = new ArrayList<>();
        users.forEach(user -> {
            Map<String, Object> singleMap = new HashMap<>();
            singleMap.put("age", user.getAge());
            singleMap.put("gender", user.getGender());
            infosFromForEach.add(singleMap);
        });
        //使用for循环转化
        List<Map<String, Object>> infosFromFor = new ArrayList<>();
        for (User user : users) {
            Map<String, Object> singleMap = new HashMap<>();
            singleMap.put("age", user.getAge());
            singleMap.put("gender", user.getGender());
            infosFromFor.add(singleMap);
        }
        //使用stream流实现转换
        List<Map<String, Object>> collect = users.stream().map(user -> {
            Map<String, Object> singleMap = new HashMap<>();
            singleMap.put("age", user.getAge());
            singleMap.put("gender", user.getGender());
            return singleMap;
        }).collect(Collectors.toList());
    }
 
 
}
 
class User {
    //姓名
    private String name;
    //年龄
    private Integer age;
    //性别:0:女;1:男
    private Integer gender;
 
    public User() {
    }
 
    public User(String name, Integer age, Integer gender) {
        this.name = name;
        this.age = age;
        this.gender = gender;
    }
 
    public String getName() {
        return name;
    }
 
    public User setName(String name) {
        this.name = name;
        return this;
    }
 
    public Integer getAge() {
        return age;
    }
 
    public User setAge(Integer age) {
        this.age = age;
        return this;
    }
 
    public Integer getGender() {
        return gender;
    }
 
    public User setGender(Integer gender) {
        this.gender = gender;
        return this;
    }
}

List<User> userList = new ArrayList<>();
List<String> nameList= userList.stream().map(User::getName).collect(Collectors.toList());

//用逗号分割
StringJoiner stringJoiner = new StringJoiner(",");

userList.forEach(user -> {
	//将实体中的某个字段获取到 添加到stringJoiner
    stringJoiner.add(user.getName());
});

//最终得到的字符串
String toString = stringJoiner.toString();

//利用Guava的Joiner
String nameListStr = Joiner,on(",").join(nameList);

//利用Apache Commons的StringUtils
String nameListStr = StringUtils.join(nameList.toArray(), ",");

String str = "hudson,zhuang,lisa";
List<String> result = Arrays.asList(str.split(","));

//例如这里将User类的集合userList按照性别进行分组
Map<String, List<User>> groupBySex = new HashMap<>();
groupBySex = userList.stream().collect(Collectors.groupingBy(User::getSex));

//获得男性集合
List<User> manList = groupBySex.get("男");

//写循环
groupBySex.keySet().for