Question about image loading problem

Question

Dear Java Gurus,
I am writing a simple Java Applet application. Basically what it does is every 3 seconds, it tries to get an image from a server and display it (also based on the browser�s client size to do some resize of the image to fit the width of the browser�s client area). But frequently I got this kind of exceptions:
----------------------------- Exception 1 --------------------------------------
Uncaught error fetching image:
java.lang.ArrayIndexOutOfBoundsException
at java.lang.System.arraycopy(Native Method)
at sun.awt.image.PNGFilterInputStream.read(Unknown Source)
at java.util.zip.InflaterInputStream.fill(Unknown Source)
at java.util.zip.InflaterInputStream.read(Unknown Source)
at java.io.BufferedInputStream.fill(Unknown Source)
at java.io.BufferedInputStream.read1(Unknown Source)
at java.io.BufferedInputStream.read(Unknown Source)
at sun.awt.image.PNGImageDecoder.produceImage(Unknown Source)
at sun.awt.image.InputStreamImageSource.doFetch(Unknown Source)
at sun.awt.image.ImageFetcher.fetchloop(Unknown Source)
at sun.awt.image.ImageFetcher.run(Unknown Source)
----------------------------- Exception 2 ------------------------------------------
sun.awt.image.PNGImageDecoder$PNGException: crc corruption
at sun.awt.image.PNGImageDecoder.getChunk(Unknown Source)
at sun.awt.image.PNGImageDecoder.getData(Unknown Source)
at sun.awt.image.PNGFilterInputStream.read(Unknown Source)
at java.util.zip.InflaterInputStream.fill(Unknown Source)
at java.util.zip.InflaterInputStream.read(Unknown Source)
at java.io.BufferedInputStream.fill(Unknown Source)
at java.io.BufferedInputStream.read1(Unknown Source)
at java.io.BufferedInputStream.read(Unknown Source)
at sun.awt.image.PNGImageDecoder.produceImage(Unknown Source)
at sun.awt.image.InputStreamImageSource.doFetch(Unknown Source)
at sun.awt.image.ImageFetcher.fetchloop(Unknown Source)
at sun.awt.image.ImageFetcher.run(Unknown Source)
Which will cause the image goes to blank in the browser and also degreed down the performance, and I do not know where they are coming from. I tried to put try-catch blocks at possible method calls, but still it does not catch these kind exceptions.
---------------------------- My Source Code ----------------------------
import java.io.*;
import java.awt.*;
import java.net.*;
import java.util.*;
import java.applet.*;
import javax.swing.*;
import java.awt.event.*;
// This is for Popup Menu
class PopupListener extends MouseAdapter
JPopupMenu popup;
PopupListener(JPopupMenu popupMenu)
popup = popupMenu;
public void mousePressed(MouseEvent e)
maybeShowPopup(e);
public void mouseClicked(MouseEvent e)
maybeShowPopup(e);
public void mouseReleased(MouseEvent e)
maybeShowPopup(e);
private void maybeShowPopup(MouseEvent e)
if (e.isPopupTrigger())
popup.show(e.getComponent(), e.getX(), e.getY());
// Image Component who contains the image and will be hosted in the ScrollPane
class ImageComponent extends JComponent
Image onscrImage;
Dimension comSize;
ImageComponent(Image image)
onscrImage = image;
setDoubleBuffered(true);
comSize = new Dimension(onscrImage.getWidth(null), onscrImage.getHeight(null));
setSize(comSize);
public synchronized void paint(Graphics g)
super.paint(g);
g.drawImage(onscrImage, 0, 0, this);
public Dimension getPreferredSize()
return comSize;
// Update the image with new image
public void setImage(Image img)
onscrImage = img;
comSize = new Dimension(onscrImage.getWidth(null), onscrImage.getHeight(null));
setSize(comSize);
// The main Applet hosted in the browser
public class MWRemotingApplet extends JApplet
//Media Tracker to manage the Image loading
MediaTracker medTracker;
Image my_Image;
// ScollPane who contains the image component
JScrollPane scrollPane;
ImageComponent imgComp;
// The applet base URL and image filename passed from htm who hosted the Applet
URL base;
String filename;
// Schedules getting the image
private java.util.Timer timer;
private int delay = 3000;
private boolean bFitToBrowser = false;
private int iVScrollbarWidth = 20;
// Popup Menu
JPopupMenu jPopupMenu;
JMenuItem popupMenuItem;
public void init()
// Set the layout to GridLayout then the it can fill in the Applet
setLayout(new GridLayout());
try
// getDocumentbase gets the applet path.
base = getCodeBase();
// Get the image file name from the parameter
filename = getParameter("filename");
catch (Exception e)
JOptionPane.showMessageDialog(null, "Failed to get the path and filename of the image!", "Message", 0);
return;
// Create the Media Tracker
medTracker = new MediaTracker(this);
// Download the image from the remote server
// If the image width is greater than the width of the current browser client area
// Resize the image to fit the width
// This is because for some reason, this will lead to image not refreshing
DownloadImage();
//Add the popup menu
jPopupMenu = new JPopupMenu();
popupMenuItem = new JMenuItem("Fit to Browser");
popupMenuItem.addActionListener(new ActionListener(){
public void actionPerformed(ActionEvent event) {
bFitToBrowser = !bFitToBrowser;
if(bFitToBrowser)
popupMenuItem.setText("Original Size");
FitToBrowser();
else
popupMenuItem.setText("Fit to Browser");
DownloadImage();
if(my_Image != null)
imgComp.setImage(my_Image);
jPopupMenu.add(popupMenuItem);
// Create the image component
imgComp = new ImageComponent(my_Image);
//Add listener to the image component so the popup menu can come up.
MouseListener popupListener = new PopupListener(jPopupMenu);
imgComp.addMouseListener(popupListener);
// Create the scroll pane
scrollPane = new JScrollPane(imgComp);
scrollPane.setDoubleBuffered(true);
// Catch the resize event of the Applet
addComponentListener(new ComponentAdapter()
public void componentResized(ComponentEvent e)
super.componentResized(e);
if(bFitToBrowser)
FitToBrowser();
else
DownloadImage();
if(my_Image != null)
imgComp.setImage(my_Image);
//Add Components to the Applet.
add("Center", scrollPane);
validate();
// Start the timer to periodically download image
// from remote server
public void start()
timer = new java.util.Timer();
timer.schedule(new TimerTask()
//creates a timertask to schedule
// overrides the run method to provide functionality
public void run()
DownloadImage();
if(my_Image != null)
imgComp.setImage(my_Image);
, 0, delay);
public void stop()
timer.cancel(); //stops the timer
public synchronized void DownloadImage()
if(my_Image != null)
my_Image.flush();
my_Image = null;
try
my_Image = getImage(base, filename);
catch (Exception e)
my_Image = null;
return;
medTracker.addImage( my_Image, 0 );
try
medTracker.waitForAll();
if ( my_Image != null )
medTracker.removeImage(my_Image);
catch (InterruptedException e)
JOptionPane.showMessageDialog(null, "waitForAll failed while downloading the image!", "Message", 0);
catch(Exception e1)
System.out.println("Get Exception = " + e1.getMessage());
e1.printStackTrace();
if(bFitToBrowser)
FitToBrowser();
else if(my_Image.getWidth(null) > this.getSize().width)
FitToWidth();
// Resize the image to fit the browser width and height
public synchronized void FitToBrowser()
if(my_Image != null)
my_Image = my_Image.getScaledInstance(this.getSize().width - 5, this.getSize().height - 5, java.awt.Image.SCALE_SMOOTH);//java.awt.Image.SCALE_AREA_AVERAGING);//java.awt.Image.SCALE_SMOOTH);
medTracker.addImage( my_Image, 0 );
try
medTracker.waitForAll();
medTracker.removeImage(my_Image);
catch (InterruptedException e)
JOptionPane.showMessageDialog(null, "waitForAll failed!", "Message", 0);
catch (Exception e1)
System.out.println("Get Exception = " + e1.getMessage());
e1.printStackTrace();
// Resize the image to fit the browser width only
public synchronized void FitToWidth()
if(my_Image != null)
int fitHeight = (int)((this.getSize().width - iVScrollbarWidth)*(my_Image.getHeight(null)+0.0)/my_Image.getWidth(null));
my_Image = my_Image.getScaledInstance(this.getSize().width - iVScrollbarWidth, fitHeight, java.awt.Image.SCALE_SMOOTH);
medTracker.addImage( my_Image, 0 );
try
medTracker.waitForAll();
medTracker.removeImage(my_Image);
catch (InterruptedException e)
JOptionPane.showMessageDialog(null, "waitForAll failed!", "Message", 0);
catch (Exception e1)
System.out.println("Get Exception = " + e1.getMessage());
e1.printStackTrace();
}

Answer 1

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