import com.alibaba.fastjson.JSON;
import com.alibaba.fastjson.JSONArray;
import com.alibaba.fastjson.JSONObject;

import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

public class TestJSON {
    public static void main(String[] args) {

        /*
           最常见的key对应一个String的。
           例如：（"card_id": "233bcbf407e87789b8e471f251774f95"）
         */
        Map<String, Object> map = new HashMap<>();
        map.put("card_id", "233bcbf407e87789b8e471f251774f95");

         /*
           key 对应 Object的。
           例如："time_range": {
                                "betin_time": "2020-05-20T13:29:35.120+08:00",
                                "end_time": "2020-05-21T13:29:35.120+08:00"
                              }
          */
        Map<String, Object> map1 = new HashMap<>();
        map1.put("betin_time", "2020-05-20T13:29:35.120+08:00");
        map1.put("end_time", "2020-05-21T13:29:35.120+08:00");
        // map转String
        String object = JSON.toJSONString(map1);
        map.put("time_range", object);

        /*
           key 对应 array的。
           "objectives" : [
              {
              "unit" : "次",
              "name" : "一周购买三次商品",
              "count" : 1,
              "description" : "特价商品",
              "objective_id" : "1234"
              },
              {
              "unit" : "次",
              "name" : "一周购买六次商品",
              "count" : 2,
              "description" : "优惠商品",
              "objective_id" : "5678"
              }
            ]
         */
        Map<String, Object> map2 = new HashMap<>();
        map2.put("unit", "次");
        map2.put("name", "一周购买三次商品");
        map2.put("count", 1);
        map2.put("description", "特价商品");
        map2.put("objective_id", "1234");
        String s2 = JSON.toJSONString(map2);
        Map<String, Object> map3 = new HashMap<>();
        map3.put("unit", "次");
        map3.put("name", "一周购买六次商品");
        map3.put("count", 2);
        map3.put("description", "优惠商品");
        map3.put("objective_id", "5678");
        String s3 = JSON.toJSONString(map3);
        List array = new ArrayList<>();
        array.add(s2);
        array.add(s3);
        map.put("objectives", array);

        // 整个map转String
        String mmm = JSON.toJSONString(map);
        System.out.println("map = " + mmm);
        // String转JSONObject
        JSONObject jsonObject = JSON.parseObject(mmm);
        System.out.println("time_range = " + jsonObject.get("time_range"));
        JSONObject json = JSON.parseObject(jsonObject.get("time_range").toString());
        System.out.println("betin_time = " + json.get("betin_time"));
        System.out.println("end_time = " + json.get("end_time"));
        // String转JSONArray
        JSONArray objectives = JSON.parseArray(jsonObject.get("objectives").toString());
        for (int i = 0; i < objectives.size(); i++) {
            System.out.println("objectives中的第" + i + "个unit = " + JSON.parseObject(objectives.get(i).toString()).get("unit"));
            System.out.println("objectives中的第" + i + "个name = " + JSON.parseObject(objectives.get(i).toString()).get("name"));
            System.out.println("objectives中的第" + i + "个count = " + JSON.parseObject(objectives.get(i).toString()).get("count"));
            System.out.println("objectives中的第" + i + "个description = " + JSON.parseObject(objectives.get(i).toString()).get("description"));
            System.out.println("objectives中的第" + i + "个objective_id = " + JSON.parseObject(objectives.get(i).toString()).get("objective_id"));
            System.out.println("===========================商品分割线=================================");
        }
    }
}

Map与JSON中的各种互转