//按钮背景设置
JButton jbG1;
//静态方式设置背景图片
jbG1 = new JButton(new ImageIcon("imgs//BtList_.png"));
//动态方式更改背景图片
jbG1.setIcon(new ImageIcon(("imgs//BtList.png")));

------解决方案--------------------
Java code
package com.han;
import java.awt.BorderLayout;
import java.awt.Container;
import java.awt.Dimension;
import java.awt.FlowLayout;
import java.awt.Image;
import java.awt.Insets;
import java.awt.Toolkit;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.ComponentAdapter;
import java.awt.event.ComponentEvent;
import java.awt.image.BufferedImage;
import java.beans.PropertyVetoException;
import java.io.IOException;
import java.net.URL;

import javax.imageio.ImageIO;
import javax.swing.ImageIcon;
import javax.swing.JButton;
import javax.swing.JDesktopPane;
import javax.swing.JFrame;
import javax.swing.JInternalFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;


/**
 * 有几个技术改进：<p>
 * 1. 在desktopPane的背景图片上再加上button等组件<p>
 * 2. desktopPane的背景图片大小随着整个窗体的大小变化而变化，使图片始终能够铺满整个区域<p>
 * 3. 对于desktopPane上的所有组件不使用绝对布局而是在backLabel存在的情况下还使用布局管理器
 * @author HAN
 * 
 */
@SuppressWarnings("serial")
public class JInternalFrame_1 extends JFrame {
    JInternalFrame internalFramePersonel = null;
    JInternalFrame internalFrameCount = null;
    JInternalFrame internalFramePayment = null;
    JPanel panelInternal;
    static JDesktopPane desktopPane = null;
    static JPanel panel;
    static Container container;
    static Dimension dimensionCurrent;
    static Insets insets; // the frame border
    
    int desktopPaneWidth;
    int desktopPaneHeight;
    
    static JLabel backLabel;
    
    URL resource; // the backLabel image URL resource
    

    public JInternalFrame_1() {
        // TODO Auto-generated constructor stub
        panel = new JPanel(new FlowLayout(FlowLayout.LEFT));
        JButton buttonPersonel = new JButton("人事管理");
        JButton buttonCount = new JButton("帐套管理");
        JButton buttonPayment = new JButton("待遇管理");
        panel.add(buttonPersonel);
        panel.add(buttonCount);
        panel.add(buttonPayment);

        container = getContentPane();
        container.add(panel, BorderLayout.NORTH);
        desktopPane = new JDesktopPane();
        container.add(desktopPane, BorderLayout.CENTER);
        resource = this.getClass().getResource("/images/LightHouse.jpg");
        ImageIcon imageIcon = new ImageIcon(resource);
        backLabel = new JLabel(imageIcon);
        backLabel.setBounds(0, 0, imageIcon.getIconWidth(),
                imageIcon.getIconHeight());

        // "new Integer(Integer.MIN_VALUE)" ensures that its layer is always
        // under the others.
        desktopPane.add(backLabel, new Integer(Integer.MIN_VALUE));

        desktopPane.setDragMode(JDesktopPane.OUTLINE_DRAG_MODE);
        
        panelInternal = new JPanel(); // Creates a new JPanel with a double buffer and a flow layout.
        panelInternal.setBounds(0, 0, 300, 300);
        System.out.println(panelInternal.isOpaque());
        panelInternal.setOpaque(false);
        System.out.println(desktopPane.getWidth() + "\t" + desktopPane.getHeight());
        JButton buttonInternal = new JButton("buttonInternal");
        JButton testButton = new JButton("testButton");
        
        testButton.setBounds(200, 0, 100, 40); 
        buttonInternal.setBounds(0, 0, 100, 40); // 设置有布局管理器后，setBounds()就失效了。换句话说，setBounds()只有在没有布局管理器的情况下才有效。
        
        panelInternal.add(testButton);
        panelInternal.add(buttonInternal);
        desktopPane.add(panelInternal, new Integer(1));
        
        // the reason for non-using the inner hidden class is that the variable
        // that it will use is must be "final",
        // and this causes it can not be assigned in the inner hidden class.
        // So we use the inner class instead, which is parallel to the level
        // "method".
        buttonPersonel.addActionListener(new ButtonPersonelActionListener());

        buttonCount.addActionListener(new ButtonCountActionListener());
        buttonPayment.addActionListener(new ButtonPaymentActionListener());
        
//        System.out.println(panel.getWidth() + "\t" + panel.getHeight());
        System.out.println(panel.getPreferredSize());
        System.out.println(desktopPane.getPreferredSize());
        addComponentListener(new MyComponentListener());
        
        
    }