java - Why does the JTable header not appear in the image?

Question

I was offering advice on capturing an image of tabular data on Java API or Tool to convert tabular data into PNG image file - when the OP requested a code sample. Turns out to be harder than I thought! The JTable header vanishes from the PNG that the code writes.

PNG

Screen shot

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

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

class TableImage {

    public static void main(String[] args) throws Exception {
        Object[][] data = {
            {"Hari", new Integer(23), new Double(78.23), new Boolean(true)},
            {"James", new Integer(23), new Double(47.64), new Boolean(false)},
            {"Sally", new Integer(22), new Double(84.81), new Boolean(true)}
        };

        String[] columns = {"Name", "Age", "GPA", "Pass"};

        JTable table = new JTable(data, columns);
        JScrollPane scroll = new JScrollPane(table);
        JPanel p = new JPanel(new BorderLayout());
        p.add(scroll,BorderLayout.CENTER);

        JOptionPane.showMessageDialog(null, p);

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

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

        JOptionPane.showMessageDialog(null, new JLabel(new ImageIcon(bi)));
        ImageIO.write(bi,"png",new File("table.png"));
    }
}

Note: I checked over camickr's Screen Image class and included a call to the doLayout(Component) method. The method is useful for if a Component has never been realized on screen, but has no effect on this code (which pops the panel containing the table in an option pane before trying to render it).

What is needed in order to get the table header to render?

Update 1

Changing the line..

        p.paint(g);

..to (with an appropriate import)..

        p.paint(g);
        JTableHeader h = table.getTableHeader();
        h.paint(g);

..produces..

I'll keep tweaking it.

Update 2

kleopatra (strategy 1) & camickr (strategy 2) have provided an answer each, both of which work, & neither of which requires adding the JTable to a dummy component (which is an huge hack IMO).

While strategy 2 will crop (or expand) to 'just the table', the 1st strategy will capture the panel containing the table. This becomes problematic if the table contains many entries, showing an image of a truncated table with a scroll bar.

While strategy 1 might be further tweaked to get around that, I really like the neat simplicity of strategy 2, so it gets the tick.

As pointed out by kleopatra, there was no 'tweak' needed. So I'll try again..

Update 3

This is the image produced by the methods put forward by both camickr and kleopatra. I'd have put it twice, but to my eye, they are identical (though I have not done a pixel by pixel comparison).

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)));
    }
}

Both achieve the goal. Using camickr's method you leverage the further power of the ScreenImage API. Using kleopatra's method - about a dozen lines (less the comments and white space) of pure J2SE.

While ScreenImage is a class I will use and recommend in future, the other approach using core J2SE is what I'd probably use for this exact circumstance.

So while the 'tick' will stay with camickr, the bounty is going to kleopatra.

Answer 1

that was a tough one

Was puzzled that that header didn't show up on the image at all: it wasn't clipped or something, it wasn't painted at all. The reason for that is .. that at the time of painting the panel to the image, the header is no longer part of the hierarchy. When closing the optionPane, table.removeNotify removes the header. For adding it again, call addNotify, as in this snippet:

    JScrollPane scroll = new JScrollPane(table);
    JPanel p = new JPanel(new BorderLayout());
    p.add(scroll, BorderLayout.CENTER);
    JOptionPane.showMessageDialog(null, p);
    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();

[solved in edit] What I still don't understand why the panel shows up empty without first having been shown in the optionPane - typically some combination of ..

   p.doLayout();
   p.setSize(p.getPreferredSize()) 

... will do

Edit

last confusion solved: to force a recursive re-layout of the pane, all container along the line must be driven into believing they have a peer - validate is optimized to do nothing if not. Doing the addNotify on the panel (instead of on the table) plus validate does the trick

    //        JOptionPane.showMessageDialog(null, p);
    // 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() + 100,
            p.getHeight() + 100, BufferedImage.TYPE_INT_RGB);

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

    JOptionPane.showMessageDialog(null, new JLabel(new ImageIcon(bi)));

Not tested for side-effects.

Edit 2

Just grumbling a bit about the..

strategy 1 might be further tweaked to get around that [truncated table column]

Actually there is no tweak needed (or the the same tweak needed as for ScreenImage, depends on what you consider a tweak :) - both require to make the JScrollPane not do its job by setting the table's prefViewportSize, the exact same line in both:

    // strategy 1
    table.setPreferredScrollableViewportSize(table.getPreferredSize());
    p.addNotify();

    // strategy 2
    scroll.setColumnHeaderView(table.getTableHeader());
    table.setPreferredScrollableViewportSize(table.getPreferredSize());