Tuesday, 19 August 2008

Consuming Web Services By JavaME

The J2ME was designed for very resource-constrained hardware. As the devices get more and more powerful (N95, iPhone, HTC Android phones), the JavaME's Mobile Information Device Profiles (MIDP) desperately need an upgrade. Before JSR-271 (MIDP 3.0) is finalised Sun has recognised the poor UI capability of JavaME and released the Light Weight UI Toolkit (LWUIT) to stay competitive. Another good 3rd-party framework is J2ME Polish.

Here I attempt to call the same web services that I developed as part of a demo using JavaME and then display the results using LWUIT.

I first tried to consume the web services developed using WCF. The Sun's Wireless Toolkit (WTK2.5.2) comes with a utility to generate SOAP client proxy from WSDL. (An alternative is to use KSOAP2). However, JavaME only supports a subset of JAXP and JAX-RPC as defined in JSR-172. My web service data contract contains a DateTime field, which violates JSR-172. Also it is mapped to java.util.Calendar, which is not supported by JavaME. So I could not call the SOAP web service as it is from JavaME. I guess I will have to wait for MIDP 3.0 or even later. In any case, full SOAP web services are too much of a heavy weight for mobile devices. It is better to use RESTful services.

Fortunately, I have also developed a RESTful version of the services using NetBeans 6.1 under the project SvdemoRestful. So I created a MIDP 2.0 project named SvdemoWUIT in NetBeans and included the LWUIT JAR in the project.

There are two quick and easy ways to consume RESTful services:

The first way is to use one of NetBeans MIDP wizards to create "Mobile Client to Web Application". This wizard will take a Web Application (or a Web App project in NB) to discover the RESTful services and generates a pair of servlet (in the web app project) and mobile client (in the MIDP project) code to wrap the service. The screenshot shows the generated files highlighted in red. Using the generated mobile client in the MIDlet:

// create an instance of the mobile client proxy
WebToMobileClient client=new WebToMobileClient();

// consume the web service via the client
String keywords = client.getText("http://localhost/MySpace_Com_John.htm");
String promoXml = client.getXml(keywords);
The corresponding stdout shows:
keywords:folk songs, pop music, chinese music ,battle, action, comedy
promo:801Batman The Dark Knight
                        Meet stars in Batman in person - Chritian Bale, Michael Caine.
                Star City2008-7-30 10:00:00Batman, action

There seemed to be a bug in the wizard: it only generated methods from one web service resource of the SvdemoRestful project although I specified both resources. Therefore, I had to modify the Utility.java and WebToMobileClient.java by hand to add the missing methods.

The second way is to use the javax.microedition.io.HttpConnection and deal with the low level stuff myself. I needed to parse the Promotion XML and to populate the PromoInfo object. JavaME only offers SAX for XML parsing, so I had to get the InputStream from the HttpConnection and pass it to the SAXParser. SAX uses callback mechanism. Therefore, a XmlHandler class had to be defined.

The MIDlet code snippet:

public class SvdemoWUITMidlet extends MIDlet implements ActionListener {
    static String promoUrl="http://localhost:8080/SvdemoRestful/resources/promo";
    // data object to hold the XML contents in its corresponding fields
    PromoInfo promo=null;
    public PromoInfo getPromo() {
        return this.promo;
    public void setPromo(PromoInfo promo) {
    public void startApp() {
        HttpConnection hc=null;

        WebToMobileClient client=new WebToMobileClient();
        try {
            String keywords = client.getText("http://localhost/MySpace_Com_John.htm");
            String promoXml = client.getXml(keywords);
            hc=(HttpConnection)Connector.open(promoUrl + StringUtil.replace(keywords," ", "%20"));

        } catch (IOException ex) {
        } finally {
            try { if (hc!=null) hc.close(); }
            catch(IOException ignored) {}

    private void parse(InputStream is) {
        SAXParserFactory factory = SAXParserFactory.newInstance();
        try {
            SAXParser saxParser = factory.newSAXParser();
            InputSource inputSource = new InputSource(is);
            saxParser.parse(is,new XmlHandler(this));

        } catch (Exception ex) {

The XmlHandler.java file:

 * To change this template, choose Tools  Templates
 * and open the template in the editor.

package svdemo;

import java.util.Stack;
import org.xml.sax.Attributes;
import org.xml.sax.SAXException;
import org.xml.sax.helpers.DefaultHandler;

 * @author ROMENL
public class XmlHandler extends DefaultHandler {
    static String TAG_PROMOTION="Promotion";
    static String TAG_NAME="Name";
    static String TAG_DESCRIPTION="Description";
    static String TAG_VENUE="Venue";
    static String TAG_DATETIME="DateTime";
    private SvdemoWUITMidlet midlet;
    private PromoInfo promo=null;
    private Stack tagStack=new Stack();
    public XmlHandler(SvdemoWUITMidlet midlet) {

    public void startDocument() throws SAXException {}
    public void startElement(String uri, String localName, String qName,
    Attributes attributes) throws SAXException {
        if(TAG_PROMOTION.equals(qName)) {
            promo=new PromoInfo();
    public void characters(char[] ch, int start, int length)
            throws SAXException  {
        String chars = new String(ch, start, length).trim();

        if(chars.length() > 0) {
            String qName = (String)tagStack.peek();
            if (TAG_NAME.equals(qName)) {
            } else if(TAG_DESCRIPTION.equals(qName)){
            } else if(TAG_VENUE.equals(qName)) {
            } else if(TAG_DATETIME.equals(qName)) {

    public void endElement(String uri, String localName, String qName,
    Attributes attributes) throws SAXException  {

    public void endDocument() throws SAXException {

Finally, presenting the retrieved data on the mobile device - the initialiseForm() method in the MIDlet:

    private void initialiseForm() {
        Form f = new Form("JME LWUIT WS Demo!");
        f.setTransitionInAnimator(Transition3D.createCube(2000, false));
        f.setTransitionOutAnimator(Transition3D.createCube(2000, true));
        if(promo!=null) {
            f.addComponent(createTextArea(1, promo.getName()));

            f.addComponent(createTextArea(2, promo.getDescription()));

            f.addComponent(createTextArea(1, promo.getVenue()));

            f.addComponent(createTextArea(1, promo.getDateTime()));
        Command exitCommand = new Command("Exit");
    private Label createLabel(String labelText) {
        Label label=new Label(labelText);
        Font font=Font.createSystemFont(Font.FACE_SYSTEM, 
                Font.STYLE_BOLD, Font.SIZE_MEDIUM);
        return label;
    private TextArea createTextArea(int rows, String text) {
        TextArea ta=new TextArea(rows ,20, TextArea.ANY);
        return ta;

The following screenshots show the LWUIT 3D cube transition effect and the MIDlet output form respectively.

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