Java对象，Map，List数组等相互转换大全（详细讲解）

Java对象转 JSON字符串

JAR包


    com.alibaba
    fastjson
    1.2.47

USER类

package com.example.demo.entity;

import lombok.AllArgsConstructor;
import lombok.Data;
import lombok.NoArgsConstructor;

//需要导入lombok
@Data
@AllArgsConstructor
@NoArgsConstructor
public class User {

    private String name;
    private int age;
    private String sex;

}

package com.kuang.controller;

import com.alibaba.fastjson.JSON;
import com.alibaba.fastjson.JSONObject;
import com.kuang.pojo.User;

import java.util.ArrayList;
import java.util.List;

public class FastJsonDemo {
   public static void main(String[] args) {
       //创建一个对象
       User user1 = new User("秦疆1号", 3, "男");
       User user2 = new User("秦疆2号", 3, "男");
       User user3 = new User("秦疆3号", 3, "男");
       User user4 = new User("秦疆4号", 3, "男");
       List list = new ArrayList();
       list.add(user1);
       list.add(user2);
       list.add(user3);
       list.add(user4);

       System.out.println("*******Java对象 转 JSON字符串*******");
       String str1 = JSON.toJSONString(list);
       System.out.println("JSON.toJSonString(list)==>"+str1);
       String str2 = JSON.toJSONString(user1);
       System.out.println("JSON.toJSonString(user1)==>"+str2);

       System.out.println("n****** JSON字符串 转 Java对象*******");
       User jp_user1=JSON.parseObject(str2,User.class);
       System.out.println("JSON.parseObject(str2,User.class)==>"+jp_user1);

       System.out.println("n****** Java对象 转 JSON对象 ******");
       JSONObject jsonObject1 = (JSONObject) JSON.toJSON(user2);
       System.out.println("(JSONObject) JSON.toJSON(user2)==>"+jsonObject1.getString("name"));

       System.out.println("n****** JSON对象 转 Java对象 ******");
       User to_java_user = JSON.toJavaObject(jsonObject1, User.class);
       System.out.println("JSON.toJavaObject(jsonObject1, User.class)==>"+to_java_user);
  }
}

输出为：

*******Java对象 转 JSON字符串*******
JSON.toJSONString(list)==>[{"age":3,"name":"秦疆1号","sex":"男"},{"age":3,"name":"秦疆2号","sex":"男"},{"age":3,"name":"秦疆3号","sex":"男"},{"age":3,"name":"秦疆4号","sex":"男"}]
JSON.toJSONString(user1)==>{"age":3,"name":"秦疆1号","sex":"男"}

****** JSON字符串 转 Java对象*******
JSON.parseObject(str2,User.class)==>User(name=秦疆1号, age=3, sex=男)

****** Java对象 转 JSON对象 ******
(JSONObject) JSON.toJSON(user2)==>秦疆2号

****** JSON对象 转 Java对象 ******
JSON.toJavaObject(jsonObject1, User.class)==>User(name=秦疆2号, age=3, sex=男)

JAVA对象转MAP

jar


            commons-beanutils
            commons-beanutils
            1.9.3

package com.example.demo.controller.Demo;


import com.alibaba.fastjson.JSON;
import com.alibaba.fastjson.JSONArray;
import com.alibaba.fastjson.JSONObject;
import com.example.demo.entity.User;

import java.lang.reflect.Field;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

public class demoTest3 {

    public static void main(String[] args) throws IllegalAccessException {
        //创建一个对象
        //JAVA中将对象转为Map类型
        User user = new User();
        user.setName("闫文超");
        user.setSex("男");
        user.setAge(16);

          Map map1 = beanToMap(user);
        System.out.println("n******  Java对象 转Map*******");
        System.out.println("Map" + map1);

        Map map2 = objectToMap2(user);
        System.out.println("n******  Java对象 转Map*******");
        System.out.println("JSON.parseObject(JSON.toJSonString(obj), Map.class)==>" + map2);



    }


    
    public static Map objectToMap2(Object obj) {
        return JSON.parseObject(JSON.toJSONString(obj), Map.class);
    }

    
    public static Map beanToMap(Object object) throws IllegalAccessException {
        Map map = new HashMap();
        Field[] fields = object.getClass().getDeclaredFields();
        for (Field field : fields) {
            field.setAccessible(true);
            map.put(field.getName(), field.get(object));
        }
        return map;
    }
    
}

Map转java对象

package com.example.demo.controller.Demo;


import com.example.demo.entity.User;
import org.apache.commons.beanutils.BeanUtils;

import java.beans.BeanInfo;
import java.beans.Introspector;
import java.beans.PropertyDescriptor;
import java.lang.reflect.Method;
import java.util.HashMap;
import java.util.Map;

public class demoTest3 {

    public static void main(String[] args) throws IllegalAccessException {

        User user = new User();
        Map map = new HashMap();
        map.put("name", "闫文超");
        map.put("sex", "男");
        map.put("age", 16);
        // 将map转换为java对象（bean）
        Object user1 = transMap2Bean(map, user);
        System.out.println("n****** Map转Java对象******");
        System.out.println("工具demo1"+user1);

        Object user2 = transMapBean(map, user);
        System.out.println("n****** Map转Java对象******");
        System.out.println("工具demo2"+user2);
    }

    
    public static User transMap2Bean(Map map, Object obj) {
        if (map == null || obj == null) {
            return null;
        }
        try {
            BeanUtils.populate(obj, map);
        } catch (Exception e) {
            e.printStackTrace();
        }

        return (User) obj;
    }


    public static User transMapBean(Map map, Object obj) {
        try {
            BeanInfo beanInfo = Introspector.getBeanInfo(obj.getClass());
            PropertyDescriptor[] propertyDescriptors = beanInfo.getPropertyDescriptors();
            for (PropertyDescriptor property : propertyDescriptors) {
                String key = property.getName();
                if (map.containsKey(key)) {
                    Object value = map.get(key);
                    // 得到property对应的setter方法
                    Method setter = property.getWriteMethod();
                    setter.invoke(obj, value);
                }
            }
        } catch (Exception e) {
            e.printStackTrace();
        }
        return (User) obj;
    }
}

List转map

package com.example.面向对象1;

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

public class listdemo {

    public static void main(String[] args) {
        List list = new ArrayList<>();
        list.add("aaa");
        list.add("bbb");
        list.add("ccc");
        Map map = list.stream().collect(Collectors.toMap(key -> key, value -> value));

        System.out.println(map);
    }

}

List和Map 的相互转换

package com.example.面向对象1;

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

public class listdemo {

    public static void main(String[] args) {
        List list = new ArrayList<>();
        list.add("aaa");
        list.add("bbb");
        list.add("ccc");
        //java的
        Map map1 = list.stream().collect(Collectors.toMap(key -> key, value -> value));
        System.out.println("n********list对象 转 map*******");
        System.out.println("stream=1=>" + map1);


        List list6 = new ArrayList<>();
        list6.add(new user(1, "a"));
        list6.add(new user(2, "b"));
        list6.add(new user(3, "c"));

// 遍历
        Map keyValueMap = new HashMap<>();
        for (user keyValue : list6) {
            keyValueMap.put(keyValue.getId(), keyValue.getName());
        }
        keyValueMap.forEach((k, v) -> System.out.println(k + " ==> " + v));

// Java8 Stream
        Map ma1p1 = list6.stream().collect(Collectors.toMap(user::getId, user::getName));
        System.out.println("n********list对象 转 map*******");
        System.out.println("stream=2=>" + ma1p1);


        //todo-----------------------------------------------------------------------------------------
        //map转list
        Map map = new HashMap<>();
        map.put(10, "apple");
        map.put(20, "orange");
        map.put(30, "banana");
        map.put(40, "watermelon");
        map.put(50, "dragonfruit");
        System.out.println("n******** map转 list 获取key值 *******");
        List result = new ArrayList(map.keySet());
        result.forEach(System.out::println);

        System.out.println("n******** map转 list 获取value值 *******");
        List result2 = new ArrayList(map.values());
        result2.forEach(System.out::println);


        Map map2 = new HashMap();
        map2.put("yan", "xi");
        map2.put("wen", "huan");
        map2.put("chao", "ni");
        List list1 = new ArrayList(map2.keySet());
        List list2 = new ArrayList(map2.values());
        System.out.println("n******** map转 list 获取key值 *******");
        System.out.println("map转list获取key的值==>"+list1);
        System.out.println("n******** map转 list 获取value值 *******");
        System.out.println("map转list获取value的值==>"+ list2);


    }


//    public Map> groupList(List students) {
//        Map> map = students.stream().collect(Collectors.groupingBy(Student::getName));
//        return map;
//    }
}

List和Array的转换

package com.example.面向对象1;

import java.util.*;

public class listdemo2 {



    public static void main(String[] args) {
        //  List转换为Array
        List list1 = new ArrayList<>();

        list1.add("AAAA");

        list1.add("BBBB");

        list1.add("CCCC");

        list1.add("DDDD");
        
        String[] array = list1.toArray(new String[list1.size()]);
        for (String animal : array) {
            System.out.println(animal);
        }

        //Array转换为List
        String[] countries = {"AAAA", "BBBB", "CCCC", "DDDD"};
        List list2 = Arrays.asList(countries);
        System.out.println(list2);
    }

}

Java对象，Map，List数组等相互转换大全（详细讲解）

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