Download and view a PNG file

/*--------------------------------------------------
* ViewPng.java
*
* Download and view a png file
*
* 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 ViewPng extends MIDlet implements CommandListener
{
private Display display;
private TextBox tbMain;
private Form fmViewPng;
private Command cmExit;
private Command cmView;
private Command cmBack;

public ViewPng()
{
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/duke.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)
{
// 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 the 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
{
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();
bStrm.close();
}

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