application.java

public String loadExerciseJSONFromAsset() {
        String json;
        try {
            InputStream inputStream = getResources().openRawResource(R.raw.exercises);
            int size = inputStream.available();
            byte[] buffer = new byte[size];
            inputStream.read(buffer);
            inputStream.close();
            json = new String(buffer, "UTF-8");
        } catch (IOException exception) {
            exception.printStackTrace();
            return null;
        }
        createExercisesFromJSONString(json);
        return json;
    }

    public void createExercisesFromJSONString(String jsonString) {

        try {
            JSONObject jsonObject = new JSONObject(jsonString);
            final JSONArray jsonArray = jsonObject.getJSONArray("exercises");
            Log.d(LOG_TAG, "JSON is of type: " + jsonArray.getClass());

            realm.executeTransaction(new Realm.Transaction() {
                @Override
                public void execute(Realm realm) {
                    realm.createOrUpdateAllFromJson(Exercise.class, jsonArray);
                }
            });

        } catch (JSONException exception) {
            exception.printStackTrace();
        }
    }