How can I analyse JSON in Java?

Question

I am doing a project for the Mobile Application Development unit. I am to read and parse the JSON from https://jsonplaceholder.typicode.com/users and display it in a list.

I am unsure on how the JSON can be parsed.

I am currently using the following script, but getting the JSONTypeMismatch error.

Any help is appreciated. Thanks in advance.

try
        {
            URL url = new URL("https://jsonplaceholder.typicode.com/users");
            con = (HttpURLConnection) url.openConnection();
            con.connect();

            JSONObject jBase = new JSONObject(IOUtils.toString(con.getInputStream(), StandardCharsets.UTF_8));

            JSONArray data = new JSONArray(IOUtils.toString(con.getInputStream(), StandardCharsets.UTF_8));
            

            for (int i = 0; i < data.length(); i++)
            {
                JSONObject user = data.getJSONObject(i);
                users.add(new User(user.getInt("id"), user.getString("name"), user.getString("username"), user.getString("email"), user.getJSONObject("address"), user.getString("phone"), user.getString("website"), user.getJSONObject("company")));
            }
        }
        catch (MalformedURLException e) {Toast.makeText(getApplicationContext(), "Malformed URL!", Toast.LENGTH_SHORT).show();}
        catch (IOException e)           {Toast.makeText(getApplicationContext(), "IOException!", Toast.LENGTH_SHORT).show();}
        catch (IllegalStateException e) {Toast.makeText(getApplicationContext(), "HTTP Error!", Toast.LENGTH_SHORT).show();}
        catch (JSONException e)         {e.printStackTrace();}
        finally                         {con.disconnect();}

Answer 1

To parse json into an object there are a couple of libraries you can use which makes it easier to parse. One of which is GSON Library

First add Gson to your app level gradle file.

  implementation 'com.google.code.gson:gson:2.9.1'

After that you can use below code to parse your required json. This is an example to parse a JSONObject to an object class. Array can be parsed a bit differently

User userModel = new Gson().fromJson(
                json.optJSONObject("data").toString(),
                User.java)

To parse JsonArray as in your case below code can be used.

Gson gson = new Gson();
String jsonOutput =  json.optJSONArray("data").toString();
Type listType = new TypeToken<List<User>>(){}.getType();
List<User> userList = gson.fromJson(jsonOutput, listType);

Answer 2

Put those library in your gradle file.

//okhttp
implementation(platform("com.squareup.okhttp3:okhttp-bom:4.9.0"))
implementation("com.squareup.okhttp3:okhttp")
implementation("com.squareup.okhttp3:logging-interceptor")
// gson
implementation 'com.google.code.gson:gson:2.9.0'

Put this line in your manifest..

<application
    ...
    android:usesCleartextTraffic="true">

</application>

Create new class as a JsonUtils.java in your project

public class JsonUtils {

public static String okhttpGET(String url) {
    OkHttpClient client = new OkHttpClient.Builder()
            .readTimeout(20000, TimeUnit.MILLISECONDS)
            .writeTimeout(20000, TimeUnit.MILLISECONDS)
            .build();

    Request request = new Request.Builder()
            .url(url)
            .build();

    try {
        Response response = client.newCall(request).execute();
        return response.body().string();
    } catch (Exception e) {
        e.printStackTrace();
        return "";
    }
}

public static String okhttpPost(String url, RequestBody requestBody) {
    OkHttpClient client = new OkHttpClient.Builder()
            .readTimeout(25000, TimeUnit.MILLISECONDS)
            .writeTimeout(25000, TimeUnit.MILLISECONDS)
            .build();

    Request request = new Request.Builder()
            .url(url)
            .post(requestBody)
            .build();

    try {
        Response response = client.newCall(request).execute();
        return response.body().string();
    } catch (Exception e) {
        e.printStackTrace();
        return "";
    }
}
}

Now time to read Json from URL , so here your url is GET method.

so where you need to Read Json write just that code...

String json = JsonUtils.okhttpGET("https://jsonplaceholder.typicode.com/users");

try{
    JSONArray array = new JSONArray(json);
    // continue decode your Json...
       for (int i = 0; i < main_array.length(); i++) {
            JSONObject object = main_array.getJSONObject(i);

            String id = object.getString("id");
            String name = object.getString("name");
            String username = object.getString("username");
            String email = object.getString("email");

            JSONObject address_object = object.getJSONObject("address");

            String street = address_object.getString("street");
            String suite = address_object.getString("suite");
            String city = address_object.getString("city");
            String zipcode = address_object.getString("zipcode");

            JSONObject geo_object = address_object.getJSONObject("geo");

            String lat = object.getString("lat");
            String lng = object.getString("lng");

            String phone = object.getString("phone");
            String website = object.getString("website");
            
            JSONObject company_object = address_object.getJSONObject("company");

            String company_name = object.getString("name");
            String catchPhrase = object.getString("catchPhrase");
            String bs = object.getString("bs");


            // here you got all variables = id, name, username, email, street, suite, city, zipcode, lat, lng, phone, website, company_name, catchPhrase, bs
        }
}catch(Exception e){
    
}