Threads e Conexão Http

/*--------------------------------------------------
* ViewPngThread.java
*
* Download and view a png file. The download is
* done in the background with a separate thread 
*
* Example from the book:     Core J2ME Technology
* Copyright John W. Muchow   http://www.CoreJ2ME.com
* You may use/modify for any non-commercial purpose
*-------------------------------------------------*/
import javax.microedition.midlet.*;
import javax.microedition.lcdui.*;
import javax.microedition.io.*;
import java.io.*;

public class ViewPngThread extends MIDlet implements CommandListener
{
  private Display display;
  private TextBox tbMain;
	private Alert alStatus;
  private Form fmViewPng;
  private Command cmExit;
  private Command cmView;
  private Command cmBack;
  private static final int ALERT_DISPLAY_TIME = 3000;
  Image im = null;  

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

    // Create the Main textbox with a maximum of 75 characters
    tbMain = new TextBox("Enter url", "http://www.corej2me.com/midpbook_v1e1/ch14/bird.png", 75, 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 png 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)
    {
      // Show alert indicating we are starting a download.
      // This alert is NOT modal, it appears for
      // approximately 3 seconds (see ALERT_DISPLAY_TIME)
      showAlert("Downloading", false, tbMain);

      // Create an instance of the class that will
      // download the file in a separate thread
      Download dl = new Download(tbMain.getString(), this);
      
      // Start the thread/download
      dl.start(); 
    } 
    else if (c == cmBack)
    {
      display.setCurrent(tbMain);
    }
  }

  /*--------------------------------------------------
  * Called by the thread after attempting to download
  * an image. If the parameter is 'true' the download
  * was successful, and the image is shown on a form. 
  * If  parameter is 'false' the download failed, and
  * the user is returned to the textbox.  
  *
  * In either case, show an alert indicating the 
  * the result of the download.
  *-------------------------------------------------*/
  public void showImage(boolean flag)
  {
    // Download failed... 
    if (flag == false)
    {
      // Alert followed by the main textbox
      showAlert("Download Failure", true, tbMain);
    }
    else  // Successful download...
    {
      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);

      // Alert followed by the form holding the image      
      showAlert("Download Successful", true, fmViewPng);
    }      
  }
  
  /*--------------------------------------------------
  * Show an alert with the parameters determining
  * the type (modal or not) and the displayable to
  * show after the alert is dismissed
  *-------------------------------------------------*/
  public void showAlert(String msg, boolean modal, Displayable displayable)
  {
     // Create alert, add text, associate a sound
    alStatus = new Alert("Status", msg, null, AlertType.INFO);

    // Set the alert type
    if (modal)
      alStatus.setTimeout(Alert.FOREVER);
    else
      alStatus.setTimeout(ALERT_DISPLAY_TIME);

    // Show the alert, followed by the displayable
    display.setCurrent(alStatus, displayable);
  }
}

/*--------------------------------------------------
* Class - Download
*
* Download an image file in a separate thread
*-------------------------------------------------*/  
class Download implements Runnable
{
  private String url;
  private ViewPngThread MIDlet;
  private boolean downloadSuccess = false;  
  
  public Download(String url, ViewPngThread MIDlet)
  { 
    this.url = url;
    this.MIDlet = MIDlet;
  }

  /*--------------------------------------------------
  * Download the image
  *-------------------------------------------------*/
  public void run() 
  {
    try
    {
      getImage(url);
    }
    catch (Exception e)
    { 
      System.err.println("Msg: " + e.toString());
    }      
  }

  /*--------------------------------------------------
  * Create and start the new thread
  *-------------------------------------------------*/  
  public void start()
  {
    Thread thread = new Thread(this);
    try
    {
      thread.start();
    }
    catch (Exception e)
    {
    }
  }
  
  /*--------------------------------------------------
  * Open connection and download png into a byte array.
  *-------------------------------------------------*/
  private void getImage(String url) throws IOException
  {
    ContentConnection connection = (ContentConnection) Connector.open(url);
    
    // * There is a bug in MIDP 1.0.3 in which read() sometimes returns
    //   an invalid length. To work around this, I have changed the 
    //   stream to DataInputStream and called readFully() instead of read()
//    InputStream iStrm = connection.openInputStream();
    DataInputStream iStrm = connection.openDataInputStream();    
    
    ByteArrayOutputStream bStrm = null;
    Image im = null;

    try
    {
      // ContentConnection includes a length method
      byte imageData[];      
      int length = (int) connection.getLength();
      if (length != -1)
      {
        imageData = new byte[length];

        // Read the png into an array        
//        iStrm.read(imageData);        
        iStrm.readFully(imageData);
      }
      else  // Length not available...
      {       
        bStrm = new ByteArrayOutputStream();
        
        int ch;
        while ((ch = iStrm.read()) != -1)
          bStrm.write(ch);
        
        imageData = bStrm.toByteArray();
      }
 
      // Create the image from the byte array
      im = Image.createImage(imageData, 0, imageData.length);        
    }
    finally
    {
      // Clean up
      if (connection != null)
        connection.close();      
      if (iStrm != null)
        iStrm.close();
      if (bStrm != null)
        bStrm.close();                        
    }

    // Return to the caller the status of the download
    if (im == null)
      MIDlet.showImage(false);
    else
    {
      MIDlet.im = im;
      MIDlet.showImage(true);              
    }
  }
}