JTable to image?

Question

Hi all,
I have an application that uses a JTable to display various data from our database. My problem is that I now need to display this same information via the web as an image. This is the requirement and no way around it. I didn't want to have to get into dynamically drawing everything using Java 2D, etc. So...Is there anyway that I can create the JTable from a Servlet and return the "image" in some format? I'm looking for a quick and simple approach. Any help would be greatly appreciated.
Matt

Answer 1

A component is not realized until you call either pack or setVisible on it.
I've modified the demo to show this. Try it first with only the top and bottom buttons (ie,without the realize gui button) and next with the bottom two.
Although the table will have a preferred size the component that will paint itself into the new BufferedImage does not yet exist so requests (in the saveComponentAsImage method) for its width and height return zero.
If you replace the saveComponentAsImage method calls getWidth and getHeight with getPreferredSize().width and getPreferredSize().height you get a blank image, nobody home.
import java.awt.*;
import java.awt.event.*;
import java.awt.image.BufferedImage;
import java.io.*;
import java.net.*;
import javax.imageio.ImageIO;
import javax.swing.*;
public class TableToImage
    public static void main(String[] args)
        final JButton
            tableButton = new JButton("make table"),
            guiButton   = new JButton("realize gui"),
            saveButton  = new JButton("save");
        ActionListener l = new ActionListener()
            JTable table;
            public void actionPerformed(ActionEvent e)
                JButton button = (JButton)e.getSource();
                if(button == tableButton)
                    table = makeTable();
                if(button == guiButton)
                    realizeGUI(table);
                if(button == saveButton)
                    Dimension
                        size = table.getSize(),
                        preferredSize = table.getPreferredSize();
                    if(size.width == 0 || size.height == 0)
                        System.out.println("actual size: width = " + size.width + "\t" +
                                           "height = " + size.height + "\n" +
                                           "preferredSize: width = " +
                                            preferredSize.width + "\t" +
                                           "height = " + preferredSize.height);
                        return;             // avoid IllegalArgumentException
                    saveComponentAsImage(table);
        tableButton.addActionListener(l);
        guiButton.addActionListener(l);
        saveButton.addActionListener(l);
        JPanel northPanel = new JPanel();
        northPanel.add(tableButton);
        JPanel panel = new JPanel();
        panel.add(guiButton);
        JPanel southPanel = new JPanel();
        southPanel.add(saveButton);
        JFrame f = new JFrame();
        f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        f.getContentPane().add(northPanel, "North");
        f.getContentPane().add(panel);
        f.getContentPane().add(southPanel, "South");
        f.setSize(200,140);
        f.setLocation(200,200);
        f.setVisible(true);
    private static JTable makeTable()
        int rows = 24, columns = 5;
        String[] headers = new String[columns];
        for(int i = 0; i < headers.length; i++)
            headers[i] = "header " + (i + 1);
        String[][] data = new String[rows][columns];
        for(int i = 0; i < rows; i++)
            for(int j = 0; j < columns; j++)
                data[i][j] = "item " + (i*columns + j + 1);
        JTable table = new JTable(data, headers);
        return table;
    private static void realizeGUI(JTable table)
        JFrame f = new JFrame();
        f.getContentPane().add(table);
        f.pack();
        f.dispose();
    private static void saveComponentAsImage(Component c)
        int w = c.getWidth();
        int h = c.getHeight();
        BufferedImage image = new BufferedImage(w, h, BufferedImage.TYPE_INT_RGB);
        Graphics2D g2 = image.createGraphics();
        c.paint(g2);
        g2.dispose();
        try
            ImageIO.write(image, "png", new File("tableImage.png"));
        catch(IOException ioe)
            System.out.println(ioe.getMessage());
}