Here is one crude example. You should be able to refine. (You may be interested in this Java "tutorial" http://docs.oracle.com/javaee/7/tutorial/doc/jsonp.htm#GLRBB

(This example uses the JSON reference implementation included in Java EE (and available here: https://java.net/projects/jsonp/downloads/directory/ri)

package com.demo;
import java.io.FileWriter;
import java.io.IOException;
import javax.json.Json;
import javax.json.stream.JsonGenerator;

public class JSONExample {
public static void main(String[] args) {
    FileWriter writer = null;
    try {
        writer = new FileWriter("C:\\Users\\Joseph White\\Downloads\\jsontext.txt");
    } catch (IOException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    }
    JsonGenerator gen = Json.createGenerator(writer);

    gen.writeStartObject().write("name", "sample")
        .writeStartArray("def")
          .writeStartObject().write("setId", 1)
             .writeStartArray("setDef")
                .writeStartObject().write("name", "ABC").write("type", "STRING")
                .writeEnd()
                .writeStartObject().write("name", "XYZ").write("type", "STRING")
                .writeEnd()
            .writeEnd()
          .writeEnd()
            .writeStartObject().write("setId", 2)
              .writeStartArray("setDef")
                .writeStartObject().write("name", "abc").write("type", "STRING")
                .writeEnd()
                .writeStartObject().write("name", "xyz").write("type", "STRING")
                .writeEnd()
              .writeEnd()
            .writeEnd()
          .writeEnd()
        .writeEnd();

    gen.close();

}

 }

Try this code using Gson library and get the things done.

Gson gson = new GsonBuilder().create();

JsonObject job = gson.fromJson(JsonString, JsonObject.class);
JsonElement entry=job.getAsJsonObject("results").getAsJsonObject("map").getAsJsonArray("entry");

String str = entry.toString();

System.out.println(str);

This standalone example seems to do what you want:

import org.json.JSONObject;

class Main {
  public static void main(String[] args) {
    JSONObject jo = new JSONObject();

    JSONObject body = new JSONObject();
    jo.put("body", body);

    JSONObject si = new JSONObject();
    body.put("studentInfo", si);
    si.put("name", "Alex James");
    si.put("id", "22284666");
    si.put("age", 13);

    System.out.println(jo.toString(4));
  }
}

Output

{"body": {"studentInfo": {
    "name": "Alex James",
    "id": "22284666",
    "age": 13
}}}

Test it on repl.it.

You will have to iterate step by step into nested JSON.

for e.g a JSON received from Google geocoding api

{
   "results" : [
      {
         "address_components" : [
            {
               "long_name" : "Bhopal",
               "short_name" : "Bhopal",
               "types" : [ "locality", "political" ]
            },
            {
               "long_name" : "Bhopal",
               "short_name" : "Bhopal",
               "types" : [ "administrative_area_level_2", "political" ]
            },
            {
               "long_name" : "Madhya Pradesh",
               "short_name" : "MP",
               "types" : [ "administrative_area_level_1", "political" ]
            },
            {
               "long_name" : "India",
               "short_name" : "IN",
               "types" : [ "country", "political" ]
            }
         ],
         "formatted_address" : "Bhopal, Madhya Pradesh, India",
         "geometry" : {
            "bounds" : {
               "northeast" : {
                  "lat" : 23.3326697,
                  "lng" : 77.5748062
               },
               "southwest" : {
                  "lat" : 23.0661497,
                  "lng" : 77.2369767
               }
            },
            "location" : {
               "lat" : 23.2599333,
               "lng" : 77.412615
            },
            "location_type" : "APPROXIMATE",
            "viewport" : {
               "northeast" : {
                  "lat" : 23.3326697,
                  "lng" : 77.5748062
               },
               "southwest" : {
                  "lat" : 23.0661497,
                  "lng" : 77.2369767
               }
            }
         },
         "place_id" : "ChIJvY_Wj49CfDkR-NRy1RZXFQI",
         "types" : [ "locality", "political" ]
      }
   ],
   "status" : "OK"
}

I shall iterate in below given fashion to "location" : { "lat" : 23.2599333, "lng" : 77.412615

//recieve JSON in json object

        JSONObject json = new JSONObject(output.toString());
        JSONArray result = json.getJSONArray("results");
        JSONObject result1 = result.getJSONObject(0);
        JSONObject geometry = result1.getJSONObject("geometry");
        JSONObject locat = geometry.getJSONObject("location");

        //"iterate onto level of location";

        double lat = locat.getDouble("lat");
        double lng = locat.getDouble("lng");

Create a Model Class for the Json, initialize it with your data. Then use Google Gson to convert it toJson also from Json to Back to the Object. and also here are two links which make your life more Easier for using Json. Online Json Editor. You can check that generated json is in the correct format or not. http://www.jsoneditoronline.org/ And Json to POJO Generated (Model Class Generator) http://www.jsonschema2pojo.org/