如何在不使用 Gson 进行类型转换的情况下将嵌套的 json 转换为 Map

Question

I am trying to understand/learn how to pull data from a weather API, i have successfully done that and i got a Json file filled with data. I managed with gson put the information into a Map.

But it also has nested json for key main were i'm pulling out value into what may by explicit typecasting.

The thing i would like to ask, is if there is a neater way of doing this and so that i don't need to do explicit type casting nested json into Map

Map<String, Object> resultMap = new Gson().fromJson(jsonString, new TypeToken<HashMap<String, Object>>() {
            }.getType());

            for (Map.Entry<String, Object> entry : resultMap.entrySet()) {
                System.out.println(entry);
            }

            System.out.println(resultMap.get("temp"));
            Map<String, Object> mainMap = (Map<String, Object>) resultMap.get("main");
            System.out.println("Temp: " + mainMap.get("temp"));

This is my output in the console:

rain={}
visibility=10000.0
timezone=7200.0
main={temp=8.1, pressure=1007.0, humidity=93.0, temp_min=7.0, temp_max=10.0}
clouds={all=75.0}
sys={type=1.0, id=1788.0, country=SE, sunrise=1.571203601E9, sunset=1.571240388E9}
dt=1.571249075E9
coord={lon=18.06, lat=59.33}
weather=[{id=301.0, main=Drizzle, description=drizzle, icon=09n}]
name=Stockholm
cod=200.0
id=2673730.0
base=stations
wind={speed=3.6, deg=40.0}
null
Temp: 8.1

Answer 1

I would say you can convert the json string into Map<String, JsonElement> so that you have so methods to find nested object is JsonObject or JsonArray . So in the blow example main is key with JsonObject as value

main: {
        temp:8.1, 
        pressure:1007.0, 
        humidity=93.0, 
        temp_min=7.0, 
        temp_max=10.0
      }

You can parse the value into Map by using fromJson

Map<String, Object> resultMap = new Gson().fromJson(jsonString, new TypeToken<Map<String, Object>>() {
        }.getType());

        for (Map.Entry<String, Object> entry : resultMap.entrySet()) {
            System.out.println(entry);
        }

        System.out.println(resultMap.get("temp"));
        Map<String, Object> mainMap = new Gson().fromJson(resultMap.get("main").toString(), new TypeToken<Map<String, Object>>() {
        }.getType());
        System.out.println("Temp: " + mainMap.get("temp"));