Implementation

For information about the design and functionality of the MIDlet, see section Design.

To create the MIDlet:

1. Create the SignedMIDlet.java class file.

2. Import the required classes and packages.

   import java.io.IOException;
   import java.io.InputStream;
   import javax.microedition.io.Connector;
   import javax.microedition.io.HttpConnection;
   import javax.microedition.lcdui.*;
   import javax.microedition.midlet.*;

3. Set SignedMIDlet to extend MIDlet and implement Runnable and CommandListener. MIDlets use the Runnable interface to execute threads and the CommandListener interface to receive high-level UI events from the platform.

   public class SignedMIDlet
           extends MIDlet
           implements Runnable, CommandListener {

4. Create the required variables and the SignedMIDlet class constructor.

       private final TextField text = new TextField("", "", 256, TextField.ANY);
       private final Form form = new Form("HTTP Result");
       private final Command exitCommand = new Command("Exit", Command.EXIT, 1);
       private final Command okCommand = new Command("Load", Command.OK, 1);
   
       public SignedMIDlet() {
       }

5. Define the mandatory lifecycle methods for starting, pausing, and destroying the MIDlet.

       public void startApp() {
           if (Display.getDisplay(this).getCurrent() == null) {
               form.setCommandListener(this);
           }
           text.setString("http://www.w3.org");
           form.addCommand(exitCommand);
           form.addCommand(okCommand);
           form.append(text);
           Display.getDisplay(this).setCurrent(form);
       }
   
       public void pauseApp() {
       }
   
       public void destroyApp(boolean unconditional) {
       }

6. Use the run method to read the URL and display the bytes read on the screen. The run method calls the protected open method.

       public void run() {
           // do an action that requires permission, e.g. HTTP connection
           try {
               HttpConnection connection = (HttpConnection) Connector.open(text.getString());
               InputStream in = connection.openInputStream();
               int counter = 0;
               int ch;
               while ((ch = in.read()) != -1) {
                   counter++;
               }
               in.close();
               connection.close();
               form.append("Bytes read: " + counter+"\n");
           } catch (IOException e) {
                showAlert("Network error");
           } catch (SecurityException e) {
               showAlert("No permission to access the network");
           } catch (Exception e) {
               showAlert("An error occurred");
           }
       }
   
       private void showAlert(String text)
       {
           Alert alert = new Alert("Exception");
           alert.setString(text);
           Display.getDisplay(this).setCurrent(alert);
       }
   

7. The MIDlet calls the commandAction method when a command has been invoked. When the user selects Load, the MIDlet invokes the okCommand and starts a new thread, and the Java Virtual Machine automatically calls the run method for the new thread.

       public void commandAction(Command command, Displayable displayable) {
           if (command == exitCommand) {
               notifyDestroyed();
           } else if (command == okCommand) {
               new Thread(this).start();
           }
       }
   }