LayoutManager for different sized components without coding absolute positions

I created the following GUI.

I set all six of the GridBagConstraints (anchor, fill, gridx, gridy, weightx, weighty) for each element of the grid. That way, I could more easily keep track of what the values were for each element.

Here's the complete runnable code I used. In other words a minimal, reproducible example.

import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.Dimension;
import java.awt.GridBagConstraints;
import java.awt.GridBagLayout;

import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.SwingUtilities;

public class GridBagLayoutGUI implements Runnable {

    public static void main(String[] args) {
        SwingUtilities.invokeLater(new GridBagLayoutGUI());
    }

    @Override
    public void run() {
        JFrame frame = new JFrame("GridBagLayout GUI");
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

        frame.add(createMainPanel(), BorderLayout.CENTER);

        frame.pack();
        frame.setLocationByPlatform(true);
        frame.setVisible(true);
    }

    private JPanel createMainPanel() {
        JPanel panel = new JPanel(new GridBagLayout());
        panel.setPreferredSize(new Dimension(300, 300));

        JButton button;

        GridBagConstraints c = new GridBagConstraints();

        button = new JButton("1");
        c.fill = GridBagConstraints.NONE;
        c.anchor = GridBagConstraints.FIRST_LINE_START;
        c.weightx = 0.0d;
        c.weighty = 0.0d;
        c.gridx = 0;
        c.gridy = 0;
        panel.add(button, c);

        button = new JButton("2");
        c.fill = GridBagConstraints.HORIZONTAL;
        c.anchor = GridBagConstraints.CENTER;
        c.weightx = 1.0d;
        c.weighty = 0.0d;
        c.gridx = 1;
        c.gridy = 0;
        panel.add(button, c);

        button = new JButton("3");
        c.fill = GridBagConstraints.NONE;
        c.anchor = GridBagConstraints.FIRST_LINE_END;
        c.weightx = 0.0d;
        c.weighty = 0.0d;
        c.gridx = 2;
        c.gridy = 0;
        panel.add(button, c);

        button = new JButton("4");
        c.fill = GridBagConstraints.VERTICAL;
        c.anchor = GridBagConstraints.LINE_START;
        c.weightx = 0.0d;
        c.weighty = 1.0d;
        c.gridx = 0;
        c.gridy = 1;
        panel.add(button, c);

        // Panel
        JPanel innerPanel = new JPanel();
        innerPanel.setBackground(Color.green.darker());
        c.fill = GridBagConstraints.BOTH;
        c.anchor = GridBagConstraints.CENTER;
        c.weightx = 1.0d;
        c.weighty = 1.0d;
        c.gridx = 1;
        c.gridy = 1;
        panel.add(innerPanel, c);

        button = new JButton("5");
        c.fill = GridBagConstraints.VERTICAL;
        c.anchor = GridBagConstraints.LINE_END;
        c.weightx = 0.0d;
        c.weighty = 1.0d;
        c.gridx = 2;
        c.gridy = 1;
        panel.add(button, c);

        button = new JButton("6");
        c.fill = GridBagConstraints.NONE;
        c.anchor = GridBagConstraints.LAST_LINE_START;
        c.weightx = 0.0d;
        c.weighty = 0.0d;
        c.gridx = 0;
        c.gridy = 2;
        panel.add(button, c);

        button = new JButton("7");

        c.fill = GridBagConstraints.HORIZONTAL;
        c.anchor = GridBagConstraints.CENTER;
        c.weightx = 1.0d;
        c.weighty = 0.0d;
        c.gridx = 1;
        c.gridy = 2;
        panel.add(button, c);

        button = new JButton("8");
        c.fill = GridBagConstraints.NONE;
        c.anchor = GridBagConstraints.LAST_LINE_END;
        c.weightx = 0.0d;
        c.weighty = 0.0d;
        c.gridx = 2;
        c.gridy = 2;
        panel.add(button, c);

        return panel;
    }

}

Another option would be JGoodies FormLayout. I have been using this in combination with JFormDesigner for all my layouting needs since basically forever. It covers 95% percent of my use cases. The remaining 5% is BorderLayout and absolute positioning (null layout).

A common strategy to solve complex computing tasks, is to break them into small, well defined manageable tasks. Divide and conquer. This also applies to gui: you can break the design into small, easy to layout containers. In this case the needed layout can be achieved by using BoxLayout and BorderLayout:

import java.awt.*;
import javax.swing.Box.Filler;
import javax.swing.*;


public class FramedContent extends JPanel{

    private static final int FRAME_WIDTH = 35, CONTENT_SIZE = 300, BORDER_SIZE = 1;
    private static final Color CORNER_COLOR = Color.MAGENTA, RULLER_COLOR = Color.BLUE,
                                CONTENT_COLOR = Color.GREEN, BORDER_COLOR = Color.WHITE;
    FramedContent(){
        setLayout(new BorderLayout());
        add(header(), BorderLayout.NORTH);
        add(center(), BorderLayout.CENTER);
        add(header(), BorderLayout.SOUTH);
    }

    private JPanel header(){
        JPanel hExpandPane = new JPanel();
        hExpandPane.setLayout(new BoxLayout(hExpandPane, BoxLayout.X_AXIS));
        hExpandPane.add(corner());
        hExpandPane.add(hRuller());
        hExpandPane.add(corner());
        return hExpandPane;
    }

    private JComponent corner(){
        Dimension d = new Dimension(FRAME_WIDTH, FRAME_WIDTH);
        Filler filler = new Filler(d, d, d);
        filler.setBackground(CORNER_COLOR);
        filler.setBorder(BorderFactory.createLineBorder(BORDER_COLOR, BORDER_SIZE));
        filler.setOpaque(true);
        return filler;
    }

    private JComponent hRuller(){
        Dimension d = new Dimension(0,FRAME_WIDTH);
        Filler filler = new Filler(d, d, new Dimension(Short.MAX_VALUE, FRAME_WIDTH));
        filler.setBackground(RULLER_COLOR);;
        filler.setOpaque(true);
        return filler;
    }

    private JPanel center(){
        JPanel vExpandPane = new JPanel();
        vExpandPane.setLayout(new BorderLayout());
        vExpandPane.add(vRuller(), BorderLayout.WEST);
        vExpandPane.add(content(), BorderLayout.CENTER);
        vExpandPane.add(vRuller(), BorderLayout.EAST);
        return vExpandPane;
    }

    private JComponent vRuller(){
        Dimension d = new Dimension(FRAME_WIDTH, 0);
        Filler filler = new Filler(d, d, new Dimension(FRAME_WIDTH, Short.MAX_VALUE));
        filler.setBackground(RULLER_COLOR);
        filler.setOpaque(true);
        return filler;
    }

    private JPanel content(){
        JPanel content = new JPanel(new GridBagLayout());// GridBagLayout used just to center the content
        content.setBackground(CONTENT_COLOR);
        content.add(new JLabel("Your Content Goes Here"));
        content.setPreferredSize(new Dimension(CONTENT_SIZE,CONTENT_SIZE));
        return content;
    }

    public static void createWindow()   {
        JFrame frame = new JFrame("Framed content");
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setLocationRelativeTo(null);
        frame.add(new FramedContent());
        frame.pack();
        frame.setVisible(true);
    }

    public static void main(String[] args) {
        createWindow();
    }
}