Advanced Mobile Features

Providing a Fallback UI

You may need to use the same URL and hence the same servlet for both the mobile TouchKit UI and for regular browsers. In this case, you need to recognize the mobile browsers compatible with Vaadin TouchKit and provide a fallback UI for any other browsers. The fallback UI can be a regular Vaadin UI, a "Sorry!" message, or a redirection to an alternate user interface.

You can handle the fallback logic in a custom UIProvider that creates the UIs in the servlet. As TouchKit supports only WebKit and Windows Phone browsers, you can do the recognition by checking if the user-agent string contains the sub-strings " webkit" or " windows phone" as follows:

public class MyUIProvider extends UIProvider {
    public Class<? extends UI>
              getUIClass(UIClassSelectionEvent event) {
        String ua = event.getRequest()
        if (   ua.toLowerCase().contains("webkit")
            || ua.toLowerCase().contains("windows phone 8")
            || ua.toLowerCase().contains("windows phone 9")) {
            return MyUI.class;
        } else {
            return MyFallbackUI.class;

The custom UI provider has to be added in a custom servlet class, which you need to define in the web.xml, as described in "TouchKit Settings". For example, as follows:

public class MyServlet extends TouchKitServlet {
    private MyUIProvider uiProvider = new MyUIProvider();

    protected void servletInitialized() throws ServletException {

                new SessionInitListener() {
            public void sessionInit(SessionInitEvent event)
                    throws ServiceException {

        ... other custom servlet settings ...

See the Parking Demo for a working example.


The geolocation feature in TouchKit allows receiving the geographical location from the mobile device. The browser will ask the user to confirm that the web site is allowed to get the location information. Tapping Share Location gives the permission. The browser will give the position acquired by GPS, cellular positioning, or Wi-Fi positioning, as enabled in the device.

Geolocation is requested by calling the static detect() method in Geolocator. You need to provide a PositionCallback handler that is called when the device has an answer for your request. If the geolocation request succeeds, onSuccess() is called. Otherwise, for example, if the user did not allow sharing of his location, onFailure() is called. The geolocation data is provided in a Position object.

Geolocator.detect(new PositionCallback() {
    public void onSuccess(Position position) {
        double latitude  = position.getLatitude();
        double longitude = position.getLongitude();
        double accuracy  = position.getAccuracy();


    public void onFailure(int errorCode) {

The position is given as degrees with fractions in the WGS84 coordinate system used by GPS. The longitude is positive to East and negative to West of the prime meridian of WGS84. The accuracy is given in meters. In addition to the above data, the following are also provided:

  • Altitude

  • Altitude accuracy

  • Heading

  • Speed

If any of the position data is unavailable, its value will be zero.

The onFailure() is called if the positioning fails for some reason. The errorCode explains the reason. Error 1 is returned if the permission was denied, 2 if the position is unavailable, 3 on positioning timeout, and 0 on an unknown error.

Notice that geolocation can take significant time, depending on the location method used by the device. With Wi-Fi and cellular positioning, the time is usually less than 30 seconds. With unassisted GPS, it can reach 15 minutes on a fresh device and even longer if the reception is bad. However, once a location fix has been made, updates to the location will be faster. If you are making navigation software, you need to update the position data fairly frequently by calling the detect() method in Geolocator multiple times.

Displaying Position on a Map

Geographical positions are often visualized with a map. There are countless ways to do that, for example, in the Parking Demo we use the V-Leaflet add-on component.

Notice that the geolocation gives the position in the WGS84 coordinate system used by GPS. The same system is conveniently used by many Internet map services, but is not in any way universal. Further, in some countries, map data is legally required to have erroneus coordinates.

The MapView in the Parking Demo is a TouchKit navigation view that uses the LMap component from the add-on to display the map:

public class MapView extends CssLayout
      implements PositionCallback, LeafletClickListener {
    private LMap map;
    private final LMarker you = new LMarker();

Position is requested from the device when a button is clicked:

locatebutton = new Button("", new ClickListener() {
    public void buttonClick(final ClickEvent event) {
locatebutton.setWidth(30, Unit.PIXELS);
locatebutton.setHeight(30, Unit.PIXELS);

When TouchKit gets the position, we center the map as follows:

public void onSuccess(final Position position) {
    ParkingUI app = ParkingUI.getApp();


    // Enable centering on current position manually

private void setCenter() {
    if (map != null)

Storing Data in the Local Storage

The LocalStorage UI extension allows storing data in the HTML5 local storage from the server-side application. The storage is a singleton, which you can get with LocalStorage.get().

final LocalStorage storage = LocalStorage.get();

Storing Data

You can store data in the local storage as key-value pairs with the put() method. Both the key and value must be strings. Storing the data requires a client round-trip, so the success or failure of the store operation can be handled with an optional LocalStorageCallback.

// Editor for the value to be stored
final TextField valueEditor = new TextField("Value");

Button store = new Button("Store", new ClickListener() {
    public void buttonClick(ClickEvent event) {
        storage.put("value", valueEditor.getValue(),
                    new LocalStorageCallback() {
            public void onSuccess(String value) {

            public void onFailure(FailureEvent error) {
      "Storing Failed");

Retrieving Data from the Storage

You can retrieve data from the local storage with the get() method. It takes the key and a LocalStorageCallback to receive the retrieved value, or a failure. Retrieving the value to the server-side requires a client rount-trip and another server request is made to send the value with the callback.

storage.get("value", new LocalStorageCallback() {
    public void onSuccess(String value) {
        valueEditor.setValue(value);"Value Retrieved");

    public void onFailure(FailureEvent error) {"Failed because: " +

Uploading Content

Uploading content from a mobile device works just like with regular Vaadin applications using the Upload component.

In an offline UI or client-side code in general, you need to handle uploading differently, using a special upload widget or handler.

Server-Side Upload Component

In a server-side UI, you can use the regular Upload component described in "Upload". When choosing a file, the device will ask to select the file from files, gallery, camera, or other possible sources, depending on the device. The only difference to normal use is that the upload component must be in immediate mode.

Uploading is supported by most mobile operating systems, such as iOS, Android, and Windows RT devices, but not in some, such as WP8.

The following example shows how to implement simple upload to an in-memory storage.

// Display the image - only a placeholder first
final Image image = new Image();

// Implement both receiver that saves upload in a file and
// listener for successful upload
class ImageUploader implements Receiver, SucceededListener,
                               ProgressListener {
    final static int maxLength = 10000000;
    ByteArrayOutputStream fos = null;
    String filename;
    Upload upload;

    public ImageUploader(Upload upload) {
        this.upload = upload;

    public OutputStream receiveUpload(String filename,
                                      String mimeType) {
        this.filename = filename;
        fos = new ByteArrayOutputStream(maxLength + 1);
        return fos; // Return the output stream to write to

    public void updateProgress(long readBytes,
                               long contentLength) {
        if (readBytes > maxLength) {
  "Too big content");

    public void uploadSucceeded(SucceededEvent event) {
        // Show the uploaded file in the image viewer
        image.setSource(new StreamResource(new StreamSource() {
            public InputStream getStream() {
                byte[] bytes = fos.toByteArray();
                return new ByteArrayInputStream(bytes);
        }, filename));


Upload upload = new Upload();
ImageUploader uploader = new ImageUploader(upload);
upload.setImmediate(true); // Only button

// Wrap it in a button group to give better style
HorizontalButtonGroup group = new HorizontalButtonGroup();

The result is shown in Mobile Upload (©2001 Marko Grönroos).

Mobile Upload

Upload on the Client-Side

When making a client-side widget that handles file upload, such as for offline mode, you can use the GWT component. In such case, you need to communicate the image data to the server with an RPC call.

On a mobile device, the perhaps most common upload task is to capture images with the integrated camera. To display them in the client-side UI correctly, you want make sure that they have reasonable size and correct orientation, without making a server round-trip to do the corrections. To send them to the server, you want to avoid using too much bandwidth. The ImageUpload widget included in the lib-gwt-imageupload add-on, available from Vaadin Directory, allows launching the camera application in the device and capturing an image. It further allows defining an image manipulation pipeline with transformations to reduce the image size if necessary, correct the orientation according to EXIF data, and so forth. The corrected image is loaded to a memory buffer, which you can display in another widget, send to the server, or store in the local store.

In the following, we allow capturing an image with the camera, normalize the image and reduce its size, and reduce the size further for displaying it in a thumbnail. Notice that the image data is encoded as a URL, which can be used as such in CSS, for example.

final ImageUpload fileUpload = new ImageUpload();

// Have a separate button to initiate the upload
final VButton takePhotoButton = new VButton();
takePhotoButton.addClickHandler(new ClickHandler() {
    public void onClick(ClickEvent event) {;

// Capture images from the camera, instead of allowing to
// choose from gallery or other sources.

// Normalize the orientation and make size suitable for
// sending to server
EXIFOrientationNormalizer normalizer =
        new EXIFOrientationNormalizer();
fileUpload.addImageLoadedHandler(new ImageLoadedHandler() {
    public void onImageLoaded(ImageLoadedEvent event) {
        // Store the image data as encoded URL

// Reduce the size further for displaying a thumbnail
ImageTransformer thumbGenerator = new ImageTransformer();
thumbGenerator.addImageLoadedHandler(new ImageLoadedHandler() {
   public void onImageLoaded(ImageLoadedEvent event) {
       // Store the thumbnail image data as encoded URL

See the Parking Demo for more details about the usage of the add-on.