问用JLayer绘制边框装饰滚动工具栏按钮

EN

import java.awt.AWTEvent;
import java.awt.BorderLayout;
import java.awt.Graphics;
import java.awt.event.MouseEvent;
import javax.swing.JButton;
import javax.swing.JComponent;
import javax.swing.JFrame;
import javax.swing.JLayer;
import javax.swing.JToolBar;
import javax.swing.SwingUtilities;
import javax.swing.UIManager;
import javax.swing.UnsupportedLookAndFeelException;
import javax.swing.plaf.LayerUI;

public class JLayerButton extends JFrame {

    private JToolBar toolbar;
    private JButton button1;
    private JButton button2;
    private JButton button3;

    public JLayerButton() {
        setDefaultCloseOperation(EXIT_ON_CLOSE);
        setTitle("JLayer Button");
        setLayout(new BorderLayout());

        toolbar = new JToolBar();
        toolbar.setFloatable(false);
        toolbar.setRollover(true);
        getContentPane().add(toolbar, BorderLayout.NORTH);

        button1 = new JButton("One");
        button1.setFocusable(false);
        toolbar.add(button1);
        button2 = new JButton("Two");
        button2.setFocusable(false);
        toolbar.add(button2);
        button3 = new JButton("Three");
        button3.setFocusable(false);
        toolbar.add(button3);

        // wrap button2 in JLayer
        int componentIndex = toolbar.getComponentIndex(button2);
        JButtonLayerUI layerUI = new JButtonLayerUI();
        JLayer<JButton> layer = new JLayer<JButton>(button2, layerUI);
        layer.setLayerEventMask(AWTEvent.MOUSE_EVENT_MASK | AWTEvent.MOUSE_MOTION_EVENT_MASK);
        layer.setFocusable(false);
        toolbar.add(layer, componentIndex);

        setSize(300, 200);
        setLocationRelativeTo(null);
    }

    public static void main(String[] args) 
            throws ClassNotFoundException, InstantiationException, 
            IllegalAccessException, UnsupportedLookAndFeelException {
        UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());

        SwingUtilities.invokeLater(new Runnable() {
            @Override
            public void run() {
                new JLayerButton().setVisible(true);
            }
        });
    }

    private static class JButtonLayerUI extends LayerUI<JButton> {

        public JButtonLayerUI() {
        }

        @Override
        public void paint(Graphics g, JComponent c) {
            super.paint(g, c);
        }

        @Override
        protected void processMouseEvent(MouseEvent e, JLayer<? extends JButton> l) {
            onMouseEvent(l, e);
        }

        @Override
        protected void processMouseMotionEvent(MouseEvent e, JLayer<? extends JButton> l) {
            onMouseEvent(l, e);
        }

        private void onMouseEvent(JLayer<? extends JButton> l, MouseEvent e) {
            System.out.println(e);
        }        

    }
}