To get Image or get graphics for any JComponent

Question

My requirment is that I need to get the Graphics object for any JComponent.
I used createImage() method and tried and used getGraphics() method for the image, Iam getting NullPointer Exception.Since createImage() is giving a null value.
Help urgently needed.
Code looks something like this:
tSource is the Component iam passing to the method.Iam getting the component correctly.
JPanel compPnl = (JPanel)tSource;
Image tImage = compPnl.createImage(compPnl.getWidth(), compPnl.getHeight());
Graphics tGraph = tImage.getGraphics();
Iam getting Null value for tImage.Help needed very urgently.
Thanx in advance

Answer 1

Try this: (include rt.jar in classpath when compiling and running)
import com.sun.image.codec.jpeg.*;
import java.io.*;
import java.awt.*;
import javax.swing.*;
import java.awt.image.*;
public class Image
     public static void main(String[] args)
          JFrame theGeneratorFrame = new JFrame("Raa");
          theGeneratorFrame.getContentPane().setLayout(new FlowLayout());
          JButton theButton = new JButton("Hi there!");          
          theGeneratorFrame.setVisible(true);
          theGeneratorFrame.setVisible(false);
          theGeneratorFrame.getContentPane().add(theButton);
          theGeneratorFrame.pack();
          BufferedImage theImage = (BufferedImage) theGeneratorFrame.createImage(theButton.getWidth(), theButton.getHeight());
          theButton.paint(theImage.createGraphics());
          JButton theSecondButton = new JButton("Bye!");
          theGeneratorFrame.getContentPane().add(theSecondButton);
          theGeneratorFrame.pack();
          BufferedImage theSecondImage = (BufferedImage) theGeneratorFrame.createImage(theSecondButton.getWidth(), theSecondButton.getHeight());
          theSecondButton.paint(theSecondImage.createGraphics());
          try
               FileOutputStream theStream = new FileOutputStream("button.jpg");
               JPEGImageEncoder theEncoder = JPEGCodec.createJPEGEncoder(theStream);
               theEncoder.encode(theImage);
               theStream.close();
               theStream = new FileOutputStream("secondbutton.jpg");
               theEncoder = JPEGCodec.createJPEGEncoder(theStream);
               theEncoder.encode(theSecondImage);
          catch (Exception e)
          {e.printStackTrace();}
}The key in this one is that I add the button to the JFrame and call pack(), because otherwise the button doesn't know its dimensions, and they will remain 0. It doesn't matter that the JFrame is invisible, since I have already shown it once, then hidden it again. (the two setVisible() ones in a row).
This approach should be usable on any component.
Just ignore the JPEG encoder bit; I just chose to save the images to file as proof of concept...as so many have already pointed out, the stuff in rt.jar shouldn't be used this way.
HTH,
F