J2ME 101, Part 4: The Generic Connection Framework

/*--------------------------------------------------
* DownloadImage.java
*
* Download and view a png file
*-------------------------------------------------*/
import javax.microedition.midlet.*;
import javax.microedition.lcdui.*;
import javax.microedition.io.*;
import java.io.*;

public class DownloadImage extends MIDlet implements CommandListener
{
  private Display display;
  private TextBox tbMain;
  private Form fmViewPng;
  private Command cmExit;
  private Command cmView;
  private Command cmBack;

  public DownloadImage()
  {
    display = Display.getDisplay(this);

    // Create the textbox, allow maximum of 50 characters
    tbMain = new TextBox("Enter url", "http://www.corej2me.com/ibm/boat.png", 55, 0);

    // Create commands and add to textbox
    cmExit = new Command("Exit", Command.EXIT, 1);
    cmView = new Command("View", Command.SCREEN, 2);
    tbMain.addCommand(cmExit);
    tbMain.addCommand(cmView );

    // Set up a listener for textbox
    tbMain.setCommandListener(this);

    // Create the form that will hold the image
    fmViewPng = new Form("");

    // Create commands and add to form
    cmBack = new Command("Back", Command.BACK, 1);
    fmViewPng.addCommand(cmBack);

    // Set up a listener for form
    fmViewPng.setCommandListener(this);
  }

  public void startApp()
  {
    display.setCurrent(tbMain);
  }

  public void pauseApp()
  { }

  public void destroyApp(boolean unconditional)
  { }

  /*--------------------------------------------------
  * Process events
  *-------------------------------------------------*/
  public void commandAction(Command c, Displayable s)
  {
    // If the Command button pressed was "Exit"
    if (c == cmExit)
    {
      destroyApp(false);
      notifyDestroyed();
    }
    else if (c == cmView)
    {
      // Download image and place on the form
      try
      {
        Image im;
        if ((im = getImage(tbMain.getString())) != null)
        {
          ImageItem ii = new ImageItem(null, im, ImageItem.LAYOUT_DEFAULT, null);

          // If there is already an image, set (replace) it
          if (fmViewPng.size() != 0)
            fmViewPng.set(0, ii);
          else  // Append the image to the empty form
            fmViewPng.append(ii);
        }
        else
          fmViewPng.append("Unsuccessful download.");

        // Display the form with image
        display.setCurrent(fmViewPng);
      }
      catch (Exception e)
      {
        System.err.println("Msg: " + e.toString());
      }
    }
    else if (c == cmBack) {
      display.setCurrent(tbMain);
    }
  }

  /*--------------------------------------------------
  * Open connection and download png into a byte array.
  *-------------------------------------------------*/
  private Image getImage(String url) throws IOException
  {
    InputStream iStrm = (InputStream) Connector.openInputStream(url);
    Image im = null;

    try
    {
      ByteArrayOutputStream bStrm = new ByteArrayOutputStream();

      int ch;
      while ((ch = iStrm.read()) != -1)
        bStrm.write(ch);

      // Place into image array
      byte imageData[] = bStrm.toByteArray();

      // Create the image from the byte array
      im = Image.createImage(imageData, 0, imageData.length);
    }
    finally
    {
      // Clean up
      if (iStrm != null)
        iStrm.close();
    }

    return (im == null ? null : im);

  }
}