How to use new ViewModel library

viewmodel.java

/**
 * The view model class
 */
public class TestViewModel extends AndroidViewModel {
    private final StocksLiveData stocksLiveData;

    public TestViewModel(Application application) {
        super(application);

        stocksLiveData = new StocksLiveData(application);
    }

    public LiveData<ResourceModel<List<StockModel>>> getStocks(String category, boolean refresh) {
        if (stocksLiveData.getValue() == null) {
            stocksLiveData.load(category);
        } else {
            if (refresh && !stocksLiveData.getValue().status.equals(ResourceModel.Status.LOADING)) {
                stocksLiveData.load(category);
            }
        }

        return stocksLiveData;
    }

    public class StocksLiveData extends LiveData<ResourceModel<List<StockModel>>> {
        private final Context context;

        public StocksLiveData(Context context) {
            this.context = context;
        }

        @Override
        protected void onActive() {

        }

        @Override
        protected void onInactive() {

        }

        public void load(final String category) {
            setValue(ResourceModel.<List<StockModel>>loading(null));

            Single<List<StockModel>> single = Single.fromCallable(new Callable<List<StockModel>>() {
                @Override
                public List<StockModel> call() throws Exception {
                    String json = getJson("https://api.iextrading.com/1.0/tops/" + category);

                    if (json != null) {
                        Gson gson = new Gson();
                        Type typeOf = new TypeToken<List<StockModel>>() {
                        }.getType();

                        Thread.sleep(10000);

                        return gson.fromJson(json, typeOf);
                    }

                    return new ArrayList<>();
                }
            }).subscribeOn(Schedulers.io()).observeOn(AndroidSchedulers.mainThread());

            single.subscribeWith(new DisposableSingleObserver<List<StockModel>>() {
                @Override
                public void onSuccess(@NonNull List<StockModel> stockModels) {
                    setValue(ResourceModel.success(stockModels));
                }

                @Override
                public void onError(@NonNull Throwable e) {
                    setValue(ResourceModel.<List<StockModel>>error("", null));
                }
            });
        }
    }

    public String getJson(String endpoint) throws Exception {
        HttpURLConnection httpURLConnection;

        URL url = new URL(endpoint);

        httpURLConnection = (HttpURLConnection) url.openConnection();
      
        httpURLConnection.setConnectTimeout(10000);
        httpURLConnection.setReadTimeout(10000);
        httpURLConnection.connect();

        int responseCode = httpURLConnection.getResponseCode();

        if (responseCode == 200) {
            try (BufferedReader bufferedReader = new BufferedReader(new InputStreamReader(httpURLConnection.getInputStream()))) {
                StringBuilder stringBuilder = new StringBuilder();
                String line;
                while ((line = bufferedReader.readLine()) != null) {
                    stringBuilder.append(line);
                }
                return stringBuilder.toString();
            }
        }

        return null;
    }
}

/**
 * The activity class
 * NOTE: LifecycleActivity is a temporary implementation detail until Lifecycles are integrated with support
 * library. You should use AppCompatActivity once it is implemented.
 * EDIT: As of support revision 26.1.0 you can use AppCompatActivity
 */
public class ViewModelTestActivity extends LifecycleActivity {
    private TestViewModel viewModel;

    @Override
    protected void onCreate(@Nullable Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        setContentView(R.layout.activity_vm);

        viewModel = ViewModelProviders.of(this).get(TestViewModel.class);

        LiveData<ResourceModel<List<StockModel>>> liveData = viewModel.getStocks("last", false);

        findViewById(R.id.refresh).setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                viewModel.getStocks("last", true);
            }
        });

        liveData.observe(this, new Observer<ResourceModel<List<StockModel>>>() {
            @Override
            public void onChanged(@Nullable ResourceModel<List<StockModel>> resourceModel) {
                if (resourceModel != null) {
                    if (resourceModel.status.equals(ResourceModel.Status.LOADING)) {
                        findViewById(R.id.progress).setVisibility(View.VISIBLE);
                    } else if (resourceModel.status.equals(ResourceModel.Status.ERROR)) {
                        findViewById(R.id.progress).setVisibility(View.GONE);
                    } else if (resourceModel.status.equals(ResourceModel.Status.SUCCESS)) {
                        findViewById(R.id.progress).setVisibility(View.GONE);

                        TextView textView = (TextView) findViewById(R.id.text);
                        textView.setText(String.valueOf(resourceModel.data.size()));
                    }
                }
            }
        });
    }
}

/**
 * The model classes
 */
public class ResourceModel<T> {
    public enum Status {
        SUCCESS,
        ERROR,
        LOADING
    }

    public final Status status;
    public final String message;

    public final T data;

    public ResourceModel(Status status, T data, String message) {
        this.status = status;
        this.data = data;
        this.message = message;
    }

    public static <T> ResourceModel<T> success(T data) {
        return new ResourceModel<>(Status.SUCCESS, data, null);
    }

    public static <T> ResourceModel<T> error(String msg, T data) {
        return new ResourceModel<>(Status.ERROR, data, msg);
    }

    public static <T> ResourceModel<T> loading(T data) {
        return new ResourceModel<>(Status.LOADING, data, null);
    }
}

public class StockModel {
    public String symbol;
    public double price;
    public int size;
    public long time;
}