Gerar miniatura

public static Image applyScale(final ImageIcon img, final int width, final int height, final int hint) {
		final int proportionalWidth;
		final int proportionalHeight;

		final double containerRate = height / (double) width;
		final double imgRate = img.getIconHeight() / (double) img.getIconWidth();
		if (imgRate > containerRate) {
			proportionalWidth = -1;
			proportionalHeight = height;
		} else {
			proportionalWidth = width;
			proportionalHeight = -1;
		}

		return img.getImage().getScaledInstance(proportionalWidth, proportionalHeight, hint);
	}

package br.com.teste;

import java.awt.Component;
import java.awt.GridLayout;
import java.awt.Image;
import java.awt.event.MouseAdapter;
import java.awt.event.MouseEvent;
import java.awt.event.MouseListener;
import java.awt.image.BufferedImage;
import java.util.HashMap;
import java.util.Map;
import java.util.SortedMap;
import java.util.TreeMap;

import javax.swing.ImageIcon;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.border.BevelBorder;

public class CopyWindowContents {
	private JFrame window;
	JPanel mainPanel;
	private SortedMap<String, Component> components;
	private Map<String, MouseListener> listeners;

	public CopyWindowContents() {
		window = new JFrame("Janela");
		components = new TreeMap<String, Component>();
		listeners = new HashMap<String, MouseListener>();

		mainPanel = new JPanel();
		components.put("component", new JLabel("Esse texto vai ser copiado"));
		components.put("button", new JButton("Copiar"));
		for (Component component : components.values()) {
			mainPanel.add(component);
		}

		mainPanel.setLayout(new GridLayout(2, 2));
		window.setContentPane(mainPanel);

		listeners.put("buttonListener", new MouseAdapter() {
			private int currentCopy = 1;
			
			@Override
			public void mouseClicked(MouseEvent e) {
				super.mouseClicked(e);
				int iWidth = mainPanel.getPreferredSize().width;
				int iHeight = mainPanel.getPreferredSize().height;

				Image bi = getPanelCopy(iWidth, iHeight);

				JLabel copyComponent = new JLabel(new ImageIcon(applyScale(bi,iWidth/2,iHeight/2,Image.SCALE_SMOOTH)));
				copyComponent.setBorder(new BevelBorder(BevelBorder.RAISED));
				components.put("newCopy"+currentCopy, copyComponent);
				mainPanel.add(copyComponent);
				currentCopy++;

				mainPanel.repaint();
				window.pack();
			}
		});

		components.get("button").addMouseListener(
				listeners.get("buttonListener"));

		window.setBounds(100, 100, 200, 500);
		window.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
		window.pack();
		window.setVisible(true);
	}

	public Image getPanelCopy(int iWidth, int iHeight){
		BufferedImage bi = new BufferedImage(iWidth, iHeight,
				BufferedImage.TYPE_INT_RGB);
		mainPanel.paint(bi.getGraphics());
		return bi;
	}
	
	public static Image applyScale(final Image img, final int width,
			final int height, final int hint) {
		final int proportionalWidth;
		final int proportionalHeight;

		img.getHeight(null);
		final double containerRate = height / (double) width;
		final double imgRate = img.getHeight(null)
				/ (double) img.getHeight(null);
		if (imgRate > containerRate) {
			proportionalWidth = -1;
			proportionalHeight = height;
		} else {
			proportionalWidth = width;
			proportionalHeight = -1;
		}

		return img.getScaledInstance(proportionalWidth,
				proportionalHeight, hint);
	}

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