Java8将List对象转换Map

基于Java8的函数式编程概念，去实现List<Object>转换Map<String,Object>

public class DemoMian2 {
    public static void main(String[] args) {
        List<Users> usersList = new ArrayList();
        Users users = new Users();
        users.setId(1L);
        users.setName("张三");
        users.setSex("男");
        users.setCity("深圳");
        usersList.add(users);

        Users users2 = new Users();
        users2.setId(2L);
        users2.setName("张三");
        users2.setSex("男");
        users2.setCity("上海");
        usersList.add(users2);

        Users users3 = new Users();
        users3.setId(3L);
        users3.setName("张三");
        users3.setSex("男");
        users3.setCity("深圳");
        usersList.add(users3);

        Users users4 = new Users();
        users4.setId(4L);
        users4.setName("张三");
        users4.setSex("男");
        users4.setCity("上海");
        usersList.add(users4);

        Map<Long, Users> collect = usersList.stream().collect(Collectors.toMap(Users::getId, Users -> Users));
        collect.forEach((key, value) -> System.out.println(key + "-" + value));

    }

}
/*
1-Users{id=1, name='张三', sex='男', city='深圳'}
2-Users{id=2, name='张三', sex='男', city='上海'}
3-Users{id=3, name='张三', sex='男', city='深圳'}
4-Users{id=4, name='张三', sex='男', city='上海'}
*/

注意：需要转换的key不能重复，如果出现重复的话，会报错已存在key

Exception in thread "main" java.lang.IllegalStateException: Duplicate key 
Users{id=3, name='张三', sex='男', city='深圳'}

处理重复key可以使用如下模式：

package com.mars;

import java.util.*;
import java.util.function.Function;
import java.util.stream.Collectors;

/**
 * TODO
 *
 * @Author: Yizq
 * @Date: 2020/10/27 1:49 下午
 */
public class DemoMian2 {
    public static void main(String[] args) {
        List<Users> usersList = new ArrayList();
        Users users = new Users();
        users.setId(1L);
        users.setName("张三");
        users.setSex("男");
        users.setCity("深圳");
        usersList.add(users);

        Users users2 = new Users();
        users2.setId(2L);
        users2.setName("张三");
        users2.setSex("男");
        users2.setCity("上海");
        usersList.add(users2);

        Users users3 = new Users();
        users3.setId(3L);
        users3.setName("张三");
        users3.setSex("男1");
        users3.setCity("深圳");
        usersList.add(users3);

        Users users4 = new Users();
        users4.setId(3L);
        users4.setName("张三");
        users4.setSex("男2");
        users4.setCity("上海");
        usersList.add(users4);

        Map<Long, Users> collect = usersList.stream().collect(Collectors.toMap(Users::getId, Function.identity(), (key1, key2) -> key2));

        collect.forEach((key, value) -> System.out.println(key + "-" + value));

    }

}
/*
1-Users{id=1, name='张三', sex='男', city='深圳'}
2-Users{id=2, name='张三', sex='男', city='上海'}
3-Users{id=3, name='张三', sex='男2', city='上海'}
*/

使用这种方式，在处理过程中会将存在的key进行覆盖

标签：Map,Users,usersList,张三,List,users4,users2,users3,Java8
来源： https://www.cnblogs.com/xianbeier/p/14068382.html