Retrieving values from nested JSON Object

Question

I've got JSON file, which I want to parse. The JSON file ("myfile") has format as follows:

{
    "LanguageLevels": {
        "1": "Początkujący",
        "2": "ŚrednioZaawansowany",
        "3": "Zaawansowany",
        "4": "Ekspert"
    }
}

I want to retrieve value (ŚrednioZaawansowany) of Key 2 from Language Levels.

import java.io.FileNotFoundException;
import java.io.FileReader;
import java.io.IOException;
import java.util.Iterator;
import org.json.simple.JSONArray;
import org.json.simple.JSONObject;
import org.json.simple.parser.JSONParser;
import org.json.simple.parser.ParseException;

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

JSONParser parser = new JSONParser();

try {

    Object obj = parser.parse(new FileReader("myfile"); 
    JSONObject jsonObject = (JSONObject) obj;
    JSONObject jsonChildObject = (JSONObject)jsonObject.get("LanguageLevels");

What to do next? How I can iterate over it?

Answer 1

Maybe you're not using the latest version of a JSON for Java Library.

json-simple has not been updated for a long time, while JSON-Java was updated 2 month ago.

JSON-Java can be found on GitHub, here is the link to its repo: https://github.com/douglascrockford/JSON-java

After switching the library, you can refer to my sample code down below:

public static void main(String[] args) {
    String JSON = "{\"LanguageLevels\":{\"1\":\"Pocz\\u0105tkuj\\u0105cy\",\"2\":\"\\u015arednioZaawansowany\",\"3\":\"Zaawansowany\",\"4\":\"Ekspert\"}}\n";

    JSONObject jsonObject = new JSONObject(JSON);
    JSONObject getSth = jsonObject.getJSONObject("LanguageLevels");
    Object level = getSth.get("2");

    System.out.println(level);
}

And as JSON-Java open-sourced, you can read the code and its document, they will guide you through.

Hope that it helps.

Answer 2

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");

Answer 3

You can see that JSONObject extends a HashMap, so you can simply use it as a HashMap:

JSONObject jsonChildObject = (JSONObject)jsonObject.get("LanguageLevels");
for (Map.Entry in jsonChildOBject.entrySet()) {
    System.out.println("Key = " + entry.getKey() + ", Value = " + entry.getValue());
}

Answer 4

JSONArray jsonChildArray = (JSONArray) jsonChildArray.get("LanguageLevels");
    JSONObject secObject = (JSONObject) jsonChildArray.get(1);

I think this should work, but i do not have the possibility to test it at the moment..

Answer 5

To see all keys of Jsonobject use this

    String JSON = "{\"LanguageLevels\":{\"1\":\"Pocz\\u0105tkuj\\u0105cy\",\"2\":\"\\u015arednioZaawansowany\",\"3\":\"Zaawansowany\",\"4\":\"Ekspert\"}}\n";
    JSONObject obj = new JSONObject(JSON);
    Iterator iterator = obj.keys();
    String key = null;
    while (iterator.hasNext()) {
        key = (String) iterator.next();
        System.out.pritnln(key);
    } 

Answer 6

Try this, you can parse nested JSON

public static String getJsonValue(String jsonReq, String key) {
        JSONObject json = new JSONObject(jsonReq);
        boolean exists = json.has(key);
        Iterator<?> keys;
        String nextKeys;
        String val = "";
        if (!exists) {
            keys = json.keys();
            while (keys.hasNext()) {
                nextKeys = (String) keys.next();
                try {
                    if (json.get(nextKeys) instanceof JSONObject) {
                        return getJsonValue(json.getJSONObject(nextKeys).toString(), key);
                    } else if (json.get(nextKeys) instanceof JSONArray) {
                        JSONArray jsonArray = json.getJSONArray(nextKeys);
                        int i = 0;
                        if (i < jsonArray.length()) do {
                            String jsonArrayString = jsonArray.get(i).toString();
                            JSONObject innerJson = new JSONObject(jsonArrayString);
                            return getJsonValue(innerJson.toString(),key);
                        } while (i < jsonArray.length());
                    }
                } catch (Exception e) {
                    e.printStackTrace();
                }
            }
        } else {
            val = json.get(key).toString();
        }
        return val;
    }