Why does the JTable header disappear when capturing the table as an image?

Why isn't the JTable header displayed in the image?

The JTable header disappears from the PNG because the header is no longer a part of the hierarchy when the panel is painted onto the image. When an option pane is closed, the header is removed from the hierarchy. To include it again, use this snippet:

    table.addNotify();
    p.doLayout();
    BufferedImage bi = new BufferedImage(p.getWidth() + 100,
            p.getHeight() + 100, BufferedImage.TYPE_INT_RGB);

    Graphics g = bi.createGraphics();
    p.paint(g);
    g.dispose();

Here's a code snippet that captures JTable data and saves it as a PNG image, and also includes solutions from camickr and kleopatra:

import javax.swing.*;
import java.awt.*;
import java.awt.image.BufferedImage;

import javax.imageio.ImageIO;
import java.io.File;

class TableImage {

    String[] columns = {"Name", "Age", "GPA", "Pass"};
    /** Any resemblance to persons living or dead is purely incidental. */
    Object[][] data = {
        {"André", new Integer(23), new Double(47.64), new Boolean(false)},
        {"Jeanie", new Integer(23), new Double(84.81), new Boolean(true)},
        {"Roberto", new Integer(22), new Double(78.23), new Boolean(true)}
    };

    TableImage() {
    }

    public JTable getTable() {
        JTable table = new JTable(data, columns);
        table.setGridColor(new Color(115,52,158));
        table.setRowMargin(5);
        table.setShowGrid(true);

        return table;
    }

    /** Method courtesy of camickr.
    https://stackoverflow.com/questions/7369814/why-does-the-jtable-header-not-appear-in-the-image/7375655#7375655
    Requires ScreenImage class available from..
    http://tips4java.wordpress.com/2008/10/13/screen-image/ */
    public BufferedImage getImage1(JTable table) {
        JScrollPane scroll = new JScrollPane(table);

        scroll.setColumnHeaderView(table.getTableHeader());
        table.setPreferredScrollableViewportSize(table.getPreferredSize());

        JPanel p = new JPanel(new BorderLayout());
        p.add(scroll, BorderLayout.CENTER);

        BufferedImage bi = ScreenImage.createImage(p);
        return bi;
    }

    /** Method courtesy of kleopatra.
    https://stackoverflow.com/questions/7369814/why-does-the-jtable-header-not-appear-in-the-image/7372045#7372045 */
    public BufferedImage getImage2(JTable table) {
        JScrollPane scroll = new JScrollPane(table);

        table.setPreferredScrollableViewportSize(table.getPreferredSize());

        JPanel p = new JPanel(new BorderLayout());
        p.add(scroll, BorderLayout.CENTER);

        // without having been shown, fake a all-ready
        p.addNotify();

        // manually size to pref
        p.setSize(p.getPreferredSize());

        // validate to force recursive doLayout of children
        p.validate();

        BufferedImage bi = new BufferedImage(p.getWidth(), p.getHeight(), BufferedImage.TYPE_INT_RGB);

        Graphics g = bi.createGraphics();
        p.paint(g);
        g.dispose();

        return bi;
    }

    public void writeImage(BufferedImage image, String name) throws Exception {
        ImageIO.write(image,"png",new File(name + ".png"));
    }

    public static void main(String[] args) throws Exception {
        UIManager.setLookAndFeel("com.sun.java.swing.plaf.nimbus.NimbusLookAndFeel");
        TableImage ti = new TableImage();
        JTable table;
        BufferedImage bi;

        table = ti.getTable();
        bi = ti.getImage1(table);
        ti.writeImage(bi, "1");
        JOptionPane.showMessageDialog(null, new JLabel(new ImageIcon(bi)));

        table = ti.getTable();
        bi = ti.getImage2(table);
        ti.writeImage(bi, "2");
        JOptionPane.showMessageDialog(null, new JLabel(new ImageIcon(bi)));
    }
}

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