Problem about screen capture program

Hi, i have done a program which captures the screen contents to an image and stores it to one directory.

package com.example.screencapture;
import java.awt.Dimension;
import java.awt.Graphics;
import java.awt.Image;
import java.awt.Rectangle;
import java.awt.Robot;
import java.awt.Toolkit;
import java.awt.image.BufferedImage;
import java.io.File;
import java.io.IOException;
import java.text.SimpleDateFormat;
import java.util.Calendar;

import javax.imageio.ImageIO;

import com.vaadin.Application;
import com.vaadin.ui.*;
import com.vaadin.ui.Button.ClickEvent;
import com.vaadin.ui.Button.ClickListener;

@SuppressWarnings("serial")
public class ScreencaptureApplication extends Application implements ClickListener 
{
	private static Window mainWindow = new Window("Screencapture Application");
	
	private Button label = new Button("Capture");
	
	String SaveTo;
	@Override
	public void init() 
	{
		label.addListener((ClickListener)this);
		mainWindow.addComponent(label);
		setMainWindow(mainWindow);
	}

	public void buttonClick(ClickEvent event) 
	{
		Button source = event.getButton();
		if(source == label)
		{
			  try
			  {
				  Robot robot = new Robot();
			
				  Dimension d = new Dimension(Toolkit.getDefaultToolkit().getScreenSize());
				  int width = (int) d.getWidth();
				  int height = (int) d.getHeight();
		      
				  robot.delay(3000);
		 
				  Image image = robot.createScreenCapture(new Rectangle(0, 0, width, height));
		 
				  BufferedImage bi = new BufferedImage(width, height, BufferedImage.TYPE_INT_RGB);
				  Graphics g = bi.createGraphics();
				  g.drawImage(image, 0, 0, width, height, null);
				  
				  Calendar mycalendar = Calendar.getInstance();
			      SimpleDateFormat formatter = new SimpleDateFormat("yyyyMMdd_hhmmss");
			      String timeStamp = formatter.format(mycalendar.getTime());
				  
				  SaveTo = "C:/temp/SparkCapture-"+ timeStamp + ".png";

				  try 
			        {
			            BufferedImage pi = bi;
			            File outputfile = new File(SaveTo);
			            ImageIO.write(pi, "png", outputfile);			
			        } catch (IOException e) 
			        {
			            e.printStackTrace();
			        }
				  
				  getMainWindow().showNotification("Screen Captured Successfully and Saved to:\n"+SaveTo);  		        
			}catch(Exception e)
			{
				
			}
 		}
	}
}

And when I run this program in eclipse then it shows output file is saved and i found it is created there.

but when i deployed this program as a .war file on tomcat v6 it gives me one big black rectangle rather than an image
so what should i do?
Please help me.

Hi, Thank you very much for such a nice reply. I will try for Screen capture add-on. Thanks again.:D