Why Does My JTable Header Disappear When Capturing an Image?

Why is the JTable Header Missing from the Image?

When attempting to capture an image of tabular data using the Java API, the JTable header may disappear from the PNG that the code writes. This is because at the time of painting the panel to the image, the header is no longer part of the hierarchy. To resolve this issue, the addNotify method can be called on the header to add it back to the hierarchy.

Solution 1: Using ScreenImage Class (Strategy 1)

import com.tips4java.screenimage.ScreenImage;

...

// Get the table
JTable table = ti.getTable();

// Create a JScrollPane and add the table to it
JScrollPane scroll = new JScrollPane(table);

// Add the header to the scroll pane
scroll.setColumnHeaderView(table.getTableHeader());

// Set the preferred viewport size so the scroll pane doesn't affect the size
table.setPreferredScrollableViewportSize(table.getPreferredSize());

// Create a panel and add the scroll pane to it
JPanel p = new JPanel(new BorderLayout());
p.add(scroll, BorderLayout.CENTER);

// Create the image from the panel using ScreenImage
BufferedImage bi = ScreenImage.createImage(p);

Solution 2: Manually Sizing and Validating (Strategy 2)

import javax.swing.*;

...

// Get the table
JTable table = ti.getTable();

// Create a JScrollPane and add the table to it
JScrollPane scroll = new JScrollPane(table);

// Set the preferred viewport size so the scroll pane doesn't affect the size
table.setPreferredScrollableViewportSize(table.getPreferredSize());

// Create a panel and add the scroll pane to it
JPanel p = new JPanel(new BorderLayout());
p.add(scroll, BorderLayout.CENTER);

// Fake having been shown to force layout
p.addNotify();

// Set the panel size to its preferred size
p.setSize(p.getPreferredSize());

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

// Create the image from the panel
BufferedImage bi = new BufferedImage(p.getWidth(), p.getHeight(), BufferedImage.TYPE_INT_RGB);
Graphics g = bi.createGraphics();
p.paint(g);

Both strategies effectively render the table header in the captured image, while keeping the table size as intended. The choice between the two approaches depends on the specific requirements of the application.

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