Reloading and redisplay images using JScrollPane

Question

I am using
Java platform:jdk 1.4.1
Windows platform: Windows 98se
Problem:I am making one application in which i need to display images when i get
it from socket.I had used one JScrollPane over JPanel with scrollbars.But when i get the image i stored it into an Image object.
such as in my main program
screen = Toolkit.getDefaultToolkit().getImage ( "screen.jpg" );
//Draw picture first time it works fine...
paintPicture(screen);
paintPicture(Image image)
     {picpnl = new JPanel();
     picpnl.setLayout(new BorderLayout());
        image = Toolkit.getDefaultToolkit(  ).getImage(image);
//Is picpnl is unable to display image second time       
      picpnl.add(new JScrollPane(new ImageComponent(image)),BorderLayout.CENTER);
        c.add( picpnl, BorderLayout.CENTER );
        picpnl.setVisible(true);
from my refresh code:
       if(image!=null)
          image.flush();
       Runtime rt = Runtime.getRuntime();
       rt.runFinalization();
       rt.gc();
       image = null;
//is this 2nd time image not properly stored in variable image
       image = Toolkit.getDefaultToolkit().createImage( b ,0, b.length );
       paintPicture(image);
//go to paintPicture second time doesn't work
class ImageComponent extends JComponent {
  Image image;
  Dimension size;
  public ImageComponent(Image image) {
    this.image = image;
    MediaTracker mt = new MediaTracker(this);
    mt.addImage(image, 0);
    try {
      mt.waitForAll(  );
catch (InterruptedException e) {
// error ...
size = new Dimension (image.getWidth(null),
image.getHeight(null));
setSize(size);}
public void paint(Graphics g) {
     g.drawImage(image, 0, 0, this);
public Dimension getPreferredSize( ) {
return size;
The above code works fine for (the first time).But when i try to display a different socket image (the second time) it doesn't work.
I didn't know what the problem is...
---whether the previous image didn't get erased from RAM or
---the OS is not aware of the current changed image in variable (image) or the
---JScrollPane is unable to redraw it second time.
How can i display one changed image from the socket onto the JScrollPane? (the second time).
Also i want to know if we are using one file with the name "screen.jpg" and at runtime if i changed that file with another file with the same name. How can i display that changed file?Is it possible in Java or not.(Is it the limitation of Java).
I totally get frustated by reading all forums but i didn't get the answer.Please reply me soon with the complete code?
The complete source code for the problem:
(SERVER):
import javax.swing.*;
import java.awt.event.*;
import java.awt.*;
import java.text.*;
import java.io.*;
import java.net.*;
import java.util.*;
public class Remote extends JFrame
private JPanel btnpnl,picpnl;
private JButton button[];
private UIManager.LookAndFeelInfo looks[];
private static int change = 1;
private JLabel label1;
private Icon icon[];
private String names[] = { "looks","connect","control", "refresh", "auto",    "commands" };
private String iconnames[] = { "gifs/look.gif","gifs/connect.gif","gifs/control.gif","gifs/refresh.gif","gifs/auto.gif","gifs/command.gif" };
private String looknames[] = { "Motif", "Windows", "Metal" };
private int port=5000;
private ScrollablePicture picture=null;
private ServerSocket server;
private Socket client;
private ObjectInputStream ins = null;
private ObjectOutputStream ous = null;
private File file;
private String fileName;
private boolean autocontrol=true;
private Image image=null;
private Container c;
     public remote()
          super( "Remote Desktop" );
c = getContentPane();
          c.setLayout( new BorderLayout() );
//String file = "screen.jpg";
looks = UIManager.getInstalledLookAndFeels();
          btnpnl = new JPanel();
          btnpnl.setLayout( new FlowLayout() );
          button = new JButton[names.length];
          icon = new ImageIcon[iconnames.length];
          Buttonhandler handler = new Buttonhandler();
          for( int i=0; i<names.length; ++i )
icon[i] = new ImageIcon( iconnames[i] );
               button[i] = new JButton( names, icon[i] );
               button[i].addActionListener(handler);
btnpnl.add(button[i]);
          c.add( btnpnl, BorderLayout.NORTH );
          //Adding Label1
          label1 = new JLabel("LABEL1");
          c.add( label1, BorderLayout.SOUTH );
picpnl = new JPanel();
     picpnl.setLayout(new BorderLayout());
          //image = Toolkit.getDefaultToolkit( ).getImage(file);
// paintPicture(image);
          c.add( picpnl, BorderLayout.CENTER );
          //setResizable(false);
          setSize( 808, 640 );
          show();
public void paintPicture(Image image)
picpnl.add(new JScrollPane(new ImageComponent(image)),BorderLayout.CENTER);
picpnl.setVisible(true);
public class Buttonhandler implements ActionListener
          public void actionPerformed( ActionEvent e )
try{
               if( e.getActionCommand() == "looks" )
try
               label1.setText( Integer.toString( change ) );
          UIManager.setLookAndFeel( looks[change++].getClassName() );
                    SwingUtilities.updateComponentTreeUI(remote.this);
               if(change==3)
                    change=0;
catch (Exception ex)
ex.printStackTrace();
               if( e.getActionCommand() == "connect" )
                    label1.setText( "connect" );
runServer();
               if( e.getActionCommand() == "refresh" )
                    label1.setText( "refresh" );
                    ous.writeObject("refresh");
                    ous.flush();
                    recieveFile();
               if( e.getActionCommand() == "auto" )
                    label1.setText( "auto" );
                    ous.writeObject("auto");
                    button[4].setText("stop");
                    ous.flush();
                    setButton(false,false,false,false,true,false);
               auto();
               if( e.getActionCommand() == "stop" )
                    ous.writeObject("stop");
                    ous.flush();
                    button[4].setText("auto");
                    setButton(true,true,true,true,true,true);
               autocontrol=false;
          catch(Exception ef)
               ef.getMessage();
     public void auto()
          while(autocontrol)
recieveFile();
     public void setButton( boolean b1, boolean b2, boolean b3, boolean b4, boolean b5, boolean b6)
          button[0].setEnabled(b1);
          button[1].setEnabled(b2);
          button[2].setEnabled(b3);
          button[3].setEnabled(b4);
          button[4].setEnabled(b5);
          button[5].setEnabled(b6);
     public void recieveFile()
     int flag = 0;
          try{
               while(flag<=2){
               Object recieved = ins.readObject();
               System.out.println("from client:" + recieved);
switch (flag) {
case 0:
if (recieved.equals("sot")) {
System.out.println("sot recieved");
                                   flag++;
break;
               case 1:
fileName = (String) recieved;
file = new File(fileName);
                              System.out.println("fileName received");
                              flag++;
break;
               case 2:
               if (file.exists())
                    file.delete();
               byte[] b = (byte[])recieved;
               FileOutputStream ff = new FileOutputStream(fileName);
ff.write(b);
flag = 3;
if(image!=null)
                         image.flush();
                                                            Runtime rt = Runtime.getRuntime();
               rt.runFinalization();
               rt.gc();
               image = null;
          Image = Toolkit.getDefaultToolkit().createImage( b ,0, b.length );          
                    paintPicture(image);
break;
          catch(Exception e)
               e.printStackTrace();
class ImageComponent extends JComponent {
Image image;
Dimension size;
public ImageComponent(Image image) {
this.image = image;
MediaTracker mt = new MediaTracker(this);
mt.addImage(image, 0);
try {
mt.waitForAll( );
catch (InterruptedException e) {
// error ...
size = new Dimension (image.getWidth(null),
image.getHeight(null));
setSize(size);}
public void paint(Graphics g) {
     g.drawImage(image, 0, 0, this);
public Dimension getPreferredSize( ) {
return size;
     public void runServer()
     try{
               server = new ServerSocket(port);
               client = server.accept();
JOptionPane.showMessageDialog(null,"Connected");
               System.out.println("connection received from" + client.getInetAddress().getHostName());
               ous = new ObjectOutputStream( client.getOutputStream() );
ous.flush();
               ins = new ObjectInputStream( client.getInputStream() );
               System.out.println("get i/o streams");
          catch(Exception e)
               e.printStackTrace();
     public static void main(String[] args)
     remote app = new remote();
     app.addWindowListener(
          new WindowAdapter(){
                    public void windowClosing( WindowEvent e )
                         System.exit( 0 );
CLIENT code:
import java.io.*;
import java.net.*;
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import java.util.*;
import java.awt.image.*;
import javax.imageio.*;
public class Client extends JFrame
private JLabel label1;
private JButton button1;
private Socket server;
private ObjectInputStream ins=null;
private ObjectOutputStream ous=null;
private File file;
private boolean autocontrol=true;     
public Client()
     super("Client");
     Container c = getContentPane();
     ButtonHandler handler = new ButtonHandler();
     c.setLayout( new FlowLayout() );
     label1 = new JLabel("");
     button1 = new JButton("connect");
     c.add(label1);
     c.add(button1);
     button1.addActionListener(handler);
     setSize(300,300);
     show();
class ButtonHandler implements ActionListener
     public void actionPerformed(ActionEvent e)
     if(e.getActionCommand()=="connect")
               runClient();
public void runClient()
     try{     
          server = new Socket(InetAddress.getByName("127.0.0.1"),5000);
System.out.println("connected to" + server.getInetAddress().getHostName());
          ous = new ObjectOutputStream(server.getOutputStream());
     ous.flush();
          ins = new ObjectInputStream(server.getInputStream());
          System.out.println("get i/o streams");
               file = new File("screen.jpg");
          listencommands();
     }catch(Exception e)
          e.getMessage();
public void listencommands()
     try
          while(true){
          Object message = ins.readObject();
     if(message.equals("refresh"))
               screenshot();
               sendFile(file);
     if(message.equals("auto"))
               autocontrol=true;
               while(autocontrol)
                    screenshot();
                    sendFile(file);
if(message.equals("stop"))
               autocontrol = false;
     catch(Exception e)
          e.printStackTrace();
public void sendFile( File file ) throws IOException
     try{     
          System.out.println("Ready to send file");
          ous.writeObject("sot");
ous.flush();
System.out.println("sot send");
          ous.writeObject("screen.jpg");
          ous.flush();
System.out.println("fileName send");
          FileInputStream f = new FileInputStream (file);
System.out.println("fileinputstream received");
          int size = f.available();
byte array[] = new byte[size];
f.read(array,0,size);
          System.out.println("Declared array");               
                    //ous.write(size);
                    //ous.flush();
          ous.writeObject(array);
ous.flush();
          System.out.println("image send");
          catch (Exception e)
               System.out.println(e.getMessage());
public void screenshot()
try
     //Get the screen size
Dimension screenSize = Toolkit.getDefaultToolkit().getScreenSize();
     Rectangle rectangle = new Rectangle(0, 0, screenSize.width, screenSize.height);
Robot robot = new Robot();     
     BufferedImage image = robot.createScreenCapture(rectangle);
     File file;
//Save the screenshot as a jpg
     file = new File("screen.jpg");
     ImageIO.write(image, "jpg", file);
catch (Exception e)
     System.out.println(e.getMessage());
public static void main( String args[] )
          Client app = new Client();
app.addWindowListener(
          new WindowAdapter(){
                    public void windowClosing( WindowEvent e )
                         System.exit( 0 );
Steps to run code:
if everything goes fine:
1.Run the server.
2.Run the client.
3.Press connect button on server.
4.Press connect on client.
5.You get a Message box "Connected".
6.Press refresh button on Server.
7.You get the first image.
8.Press refresh button on Server.
9.You are not going to get anything but the same image.....this is where the problem begins to display that second changed image screenshot.

Answer 1

/* (SERVER): */
import javax.swing.*;
import java.awt.event.*;
import java.awt.*;
import java.text.*;
import java.io.*;
import java.net.*;
import java.util.*;
public class Remote extends JFrame
private JPanel btnpnl,picpnl;
private JButton button[];
private UIManager.LookAndFeelInfo looks[];
private static int change = 1;
private JLabel label1;
private Icon icon[];
private String names[] = { "looks","connect","control", "refresh", "auto", "commands" };
private String iconnames[] = { "gifs/look.gif","gifs/connect.gif","gifs/control.gif","gifs/refresh.gif","gifs/auto.gif","gifs/command.gif" };
private String looknames[] = { "Motif", "Windows", "Metal" };
private int port=5000;
private ScrollablePicture picture=null;
private ServerSocket server;
private Socket client;
private ObjectInputStream ins = null;
private ObjectOutputStream ous = null;
private File file;
private String fileName;
private boolean autocontrol=true;
private Image image=null;
private Container c;
public remote()
super( "Remote Desktop" );
c = getContentPane();
c.setLayout( new BorderLayout() );
//String file = "screen.jpg";
looks = UIManager.getInstalledLookAndFeels();
btnpnl = new JPanel();
btnpnl.setLayout( new FlowLayout() );
button = new JButton[names.length];
icon = new ImageIcon[iconnames.length];
Buttonhandler handler = new Buttonhandler();
for( int i=0; i<names.length; ++i )
icon = new ImageIcon( iconnames );
button = new JButton( names, icon );
button.addActionListener(handler);
btnpnl.add(button);
c.add( btnpnl, BorderLayout.NORTH );
//Adding Label1
label1 = new JLabel("LABEL1");
c.add( label1, BorderLayout.SOUTH );
picpnl = new JPanel();
picpnl.setLayout(new BorderLayout());
//image = Toolkit.getDefaultToolkit( ).getImage(file);
// paintPicture(image);
c.add( picpnl, BorderLayout.CENTER );
//setResizable(false);
setSize( 808, 640 );
show();
public void paintPicture(Image image)
picpnl.add(new JScrollPane(new ImageComponent(image)),BorderLayout.CENTER);
picpnl.setVisible(true);
public class Buttonhandler implements ActionListener
public void actionPerformed( ActionEvent e )
try{
if( e.getActionCommand() == "looks" )
try
label1.setText( Integer.toString( change ) );
UIManager.setLookAndFeel( looks[change++].getClassName() );
SwingUtilities.updateComponentTreeUI(remote.this);
if(change==3)
change=0;
catch (Exception ex)
ex.printStackTrace();
if( e.getActionCommand() == "connect" )
label1.setText( "connect" );
runServer();
if( e.getActionCommand() == "refresh" )
label1.setText( "refresh" );
ous.writeObject("refresh");
ous.flush();
recieveFile();
if( e.getActionCommand() == "auto" )
label1.setText( "auto" );
ous.writeObject("auto");
button[4].setText("stop");
ous.flush();
setButton(false,false,false,false,true,false);
auto();
if( e.getActionCommand() == "stop" )
ous.writeObject("stop");
ous.flush();
button[4].setText("auto");
setButton(true,true,true,true,true,true);
autocontrol=false;
catch(Exception ef)
ef.getMessage();
public void auto()
while(autocontrol)
recieveFile();
public void setButton( boolean b1, boolean b2, boolean b3, boolean b4, boolean b5, boolean b6)
button[0].setEnabled(b1);
button[1].setEnabled(b2);
button[2].setEnabled(b3);
button[3].setEnabled(b4);
button[4].setEnabled(b5);
button[5].setEnabled(b6);
public void recieveFile()
int flag = 0;
try{
while(flag><=2){
Object recieved = ins.readObject();
System.out.println("from client:" + recieved);
switch (flag) {
case 0:
if (recieved.equals("sot")) {
System.out.println("sot recieved");
flag++;
break;
case 1:
fileName = (String) recieved;
file = new File(fileName);
System.out.println("fileName received");
flag++;
break;
case 2:
if (file.exists())
file.delete();
byte[] b = (byte[])recieved;
FileOutputStream ff = new FileOutputStream(fileName);
ff.write(b);
flag = 3;
if(image!=null)
image.flush();
Runtime rt = Runtime.getRuntime();
rt.runFinalization();
rt.gc();
image = null;
Image = Toolkit.getDefaultToolkit().createImage( b ,0, b.length );
paintPicture(image);
break;
catch(Exception e)
e.printStackTrace();
class ImageComponent extends JComponent {
Image image;
Dimension size;
public ImageComponent(Image image) {
this.image = image;
MediaTracker mt = new MediaTracker(this);
mt.addImage(image, 0);
try {
mt.waitForAll( );
catch (InterruptedException e) {
// error ...
size = new Dimension (image.getWidth(null),
image.getHeight(null));
setSize(size);}
public void paint(Graphics g) {
g.drawImage(image, 0, 0, this);
public Dimension getPreferredSize( ) {
return size;
public void runServer()
try{
server = new ServerSocket(port);
client = server.accept();
JOptionPane.showMessageDialog(null,"Connected");
System.out.println("connection received from" + client.getInetAddress().getHostName());
ous = new ObjectOutputStream( client.getOutputStream() );
ous.flush();
ins = new ObjectInputStream( client.getInputStream() );
System.out.println("get i/o streams");
catch(Exception e)
e.printStackTrace();
public static void main(String[] args)
remote app = new remote();
app.addWindowListener(
new WindowAdapter(){
public void windowClosing( WindowEvent e )
System.exit( 0 );
/* End Server */
/*CLIENT code: */
import java.io.*;
import java.net.*;
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import java.util.*;
import java.awt.image.*;
import javax.imageio.*;
public class Client extends JFrame
private JLabel label1;
private JButton button1;
private Socket server;
private ObjectInputStream ins=null;
private ObjectOutputStream ous=null;
private File file;
private boolean autocontrol=true;
public Client()
super("Client");
Container c = getContentPane();
ButtonHandler handler = new ButtonHandler();
c.setLayout( new FlowLayout() );
label1 = new JLabel("");
button1 = new JButton("connect");
c.add(label1);
c.add(button1);
button1.addActionListener(handler);
setSize(300,300);
show();
class ButtonHandler implements ActionListener
public void actionPerformed(ActionEvent e)
if(e.getActionCommand()=="connect")
runClient();
public void runClient()
try{
server = new Socket(InetAddress.getByName("127.0.0.1"),5000);
System.out.println("connected to" + server.getInetAddress().getHostName());
ous = new ObjectOutputStream(server.getOutputStream());
ous.flush();
ins = new ObjectInputStream(server.getInputStream());
System.out.println("get i/o streams");
file = new File("screen.jpg");
listencommands();
}catch(Exception e)
e.getMessage();
public void listencommands()
try
while(true){
Object message = ins.readObject();
if(message.equals("refresh"))
screenshot();
sendFile(file);
if(message.equals("auto"))
autocontrol=true;
while(autocontrol)
screenshot();
sendFile(file);
if(message.equals("stop"))
autocontrol = false;
catch(Exception e)
e.printStackTrace();
public void sendFile( File file ) throws IOException
try{
System.out.println("Ready to send file");
ous.writeObject("sot");
ous.flush();
System.out.println("sot send");
ous.writeObject("screen.jpg");
ous.flush();
System.out.println("fileName send");
FileInputStream f = new FileInputStream (file);
System.out.println("fileinputstream received");
int size = f.available();
byte array[] = new byte[size];
f.read(array,0,size);
System.out.println("Declared array");
//ous.write(size);
//ous.flush();
ous.writeObject(array);
ous.flush();
System.out.println("image send");
catch (Exception e)
System.out.println(e.getMessage());
public void screenshot()
try
//Get the screen size
Dimension screenSize = Toolkit.getDefaultToolkit().getScreenSize();
Rectangle rectangle = new Rectangle(0, 0, screenSize.width, screenSize.height);
Robot robot = new Robot();
BufferedImage image = robot.createScreenCapture(rectangle);
File file;
//Save the screenshot as a jpg
file = new File("screen.jpg");
ImageIO.write(image, "jpg", file);
catch (Exception e)
System.out.println(e.getMessage());
public static void main( String args[] )
Client app = new Client();
app.addWindowListener(
new WindowAdapter(){
public void windowClosing( WindowEvent e )
System.exit( 0 );
}