List,Map,实体类,字符串相互转换

添加依赖

 <dependency>
     <groupId>com.alibaba</groupId>
     <artifactId>fastjson</artifactId>
     <version>1.2.7</version>
 </dependency>

List,实体类字符串想换转换

package Map;

import com.alibaba.fastjson.*;
import dto.Person;

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


public class JsonUtils {


    public static void main(String[] args) {
        List<Person> list = new ArrayList<Person>();
        Person person1 = new Person();
        person1.setName("张三");
        person1.setAge(18);
        list.add(person1);

        Map<String, String> map = new HashMap<>();
        map.put("张三", "男");
        map.put("李四", "男");
        map.put("王五", "女");


        //实体类转String
        String str = JSON.toJSONString(person1);
        //list转为String
        String strList = JSON.toJSONString(list);
        String str2 = JSONObject.toJSONString(list);
        String str3 = JSONArray.toJSONString(list);
        // map转String
        String mapStr = JSON.toJSONString(map);


        //String转实体类
        Person person = JSON.parseObject(str, Person.class);
        //String转Json对象
        JSONObject jsonObject = JSONObject.parseObject(str);
        //String转为list
        List<Person> list1 = JSON.parseArray(strList, Person.class);
        List<Person> list2 = JSONObject.parseArray(str, Person.class);
        List<Person> list3 = JSONArray.parseArray(str, Person.class);
        //String转JsonArray对象
        JSONArray jsonArray = JSONArray.parseArray(strList);
        //String转map
        Map<String, String> map1 = JSON.parseObject(mapStr,Map.class);
    }

}

List,Map相互转换(java8 stream流)

List转Map

/**

 * List -> Map

 * toMap 如果集合对象有重复的key，会报错Duplicate key ....

 *  可以用 (k1,k2)->k1 来设置，如果有重复的key,则保留key1,舍弃key2

 */

Map<String, Person> appleMap = list1.stream().collect(Collectors.toMap(Person::getName, a -> a, (k1, k2) -> k1));

Map转List

/**
* Map -> List
*/
List<Integer> result1 = map.keySet().stream().collect(Collectors.toList());
List<String> result2 = map.values().stream().collect(Collectors.toList());