BufferedImage image = new BufferedImage(jpanel.getWidth(),
jpanel.getHeight(),BufferedImage.TYPE_INT_RGB);
Graphics2D g2 = image.createGraphics();
jpanel.paint(g2);
javax.imageio.ImageIO.write(image, "jpeg", new
java.io.File("file.jpeg"));

import javax.swing.*;
import javax.imageio.*;
import java.awt.image.*;
import java.awt.*;
import java.io.*;

public class ComponentToImageFile{
 JFrame frame;
 JLabel label;
 JButton button;

 public ComponentToImageFile(){
   frame = new JFrame("ComponentToImageFile");
   frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
   label = new JLabel(new ImageIcon("siggy.jpg"));
   button = new JButton("We Love Siggy");
   Container con = frame.getContentPane();
   con.add(label, BorderLayout.CENTER);
   con.add(button, BorderLayout.SOUTH);

   frame.setBounds(0, 0, 300, 200);
   frame.setVisible(true);
 }

 public void writeFile(Component comp, String fileName){
   String ext;

   String[] temp = fileName.split("\\.");
   ext = temp[temp.length - 1];
   
//    RenderedImage rImage = comp2Image(comp);
   RenderedImage rImage = getCompImageFromRobot(comp);
   
   try{
     File file = new File(fileName);
     if (ext.equals("png")){
       ImageIO.write(rImage, "png", file);
     }  
     else if (ext.equals("jpg")){
       ImageIO.write(rImage, "jpg", file);
     }
     else{
       System.err.println("Unsupported format: " + ext);
     }
   }
   catch(IOException e){
     e.printStackTrace();
   }
 }

 
 RenderedImage getCompImageFromRobot(Component comp){
   int x, y, width, height;
   BufferedImage bImage = null;
   
   //these conditionals are necessary, but I don't know why
   if (comp instanceof Window){
     x = comp.getX();
     y = comp.getY();
   }
   else{
     Point p = comp.getLocationOnScreen();
     x = p.x;
     y = p.y;
   }
   width = comp.getWidth();
   height = comp.getHeight();
 
   Rectangle rec = new Rectangle(x, y, width, height);

   try{
     Robot robo = new Robot();
      //you need to give generous amount of delay
     robo.delay(100);
     bImage = robo.createScreenCapture(rec);
   }
   catch(Exception e){
     e.printStackTrace();
   }

   return bImage;
 }
 
 RenderedImage comp2Image(Component cmp){
   int width, height;
 
   width = cmp.getWidth();
   height = cmp.getHeight();

   BufferedImage bImage
    = new BufferedImage(width, height, BufferedImage.TYPE_INT_RGB);
   
     Graphics2D g2d = bImage.createGraphics();
   
     cmp.paint(g2d);
     g2d.dispose();
   
     return bImage;
 }

 public static void main(String[] args){

   ComponentToImageFile ctif = new ComponentToImageFile();
   ctif.writeFile(ctif.frame, "SiggyFrame.png");
   ctif.writeFile(ctif.button, "SiggyButton.png");
 }
}