How to get names of objects contained in JSON with Java?

A colleague helped me here ... I got the result I wanted with this function:

package buscaJson;

import java.io.*;
import org.json.*;

import org.json.simple.JSONObject;
import org.json.simple.parser.JSONParser;
import org.json.simple.parser.ParseException;

public class BuscaAtributos {

public static void main(String[] args) throws JSONException, IOException {

        JSONParser parser = new JSONParser();

         try {

                Object obj = parser.parse(new FileReader("teste.json"));

                JSONObject jsonObject = (JSONObject) obj;
                System.out.println(jsonObject.keySet()); 

            } catch (FileNotFoundException e) {
                e.printStackTrace();
            } catch (IOException e) {
                e.printStackTrace();
            } catch (ParseException e) {
                e.printStackTrace();
            }
    }
}

Result obtained:

[batteryCharge, temperature, id, luminousFlux]

You can use Gson :

    <dependency>
        <groupId>com.google.code.gson</groupId>
        <artifactId>gson</artifactId>
        <version>2.8.0</version>
    </dependency>

If you want to convert the entire json to object you will need to structure the classes:

code

public class Code {
    private String type;
    private String value;

   //gets e sets

}

metadata

public class Metadata {
    private Code code;

   //gets e sets

}

date

public class Data {
    private Metadata metadata;
    private String type;
    private String value;

   //gets e sets

}

and its object

public class MyOBJ {

    private String id;
    private Data batteryCharge;
    private Data luminousFlux;
    private Data temperature;

   //gets e sets

}

To use json's conversion to the object, just do this:

MyOBJ obj = new Gson().fromJson(json, MyOBJ.class);

Another way is to work directly with json, you can use org.json

    <dependency>
        <groupId>org.json</groupId>
        <artifactId>json</artifactId>
        <version>20160810</version>
    </dependency>

and work with objects this way:

    JSONObject jsonObject = new JSONObject(json);

    JSONObject batteryCharge = jsonObject.getJSONObject("batteryCharge");
    JSONObject luminousFlux = jsonObject.getJSONObject("luminousFlux");
    String id = jsonObject.getString("id");
    JSONObject temperature = jsonObject.getJSONObject("temperature");