Q的桌面截图功能非常方便，去年曾用Java模拟过一个，现整理出来。
本方法首先需要抓到屏幕的整个图象，将图象显示在一个JFrame中，再将JFrame全屏显示，这样就模拟出了一个桌面，Java也就可以获得鼠标的作用区域从而实现桌面中的小范围截屏。

   import javax.swing.*;  import java.awt.*;  import java.awt.event.ActionEvent;  import java.awt.event.ActionListener;  import java.awt.event.MouseAdapter;  import java.awt.event.MouseEvent;  import java.awt.event.MouseMotionListener;    /**   * 用Java模拟出QQ桌面截图功能   * @author 五斗米 <如转载请保留作者和出处>   * @blog <a href="http://blog.csdn.net/mq612">http://blog.csdn.net/mq612   */    public class Test extends JFrame {     private static final long serialVersionUID = -267804510087895906L;     private JButton button = null;       private JLabel imgLabel = null;     public Test() {    button = new JButton("模拟屏幕（点右键退出）");    button.addActionListener(new ActionListener() {     public void actionPerformed(ActionEvent e) {      try {       new ScreenWindow(imgLabel);      } catch (Exception e1) {       JOptionPane.showConfirmDialog(null, "出现意外错误！", "系统提示", JOptionPane.DEFAULT_OPTION, JOptionPane.ERROR_MESSAGE);      }     }    });    JPanel pane = new JPanel();    pane.setBackground(Color.WHITE);    imgLabel = new JLabel();    pane.add(imgLabel);    JScrollPane spane = new JScrollPane(pane);    this.getContentPane().add(button, BorderLayout.NORTH);    this.getContentPane().add(spane);    this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);    this.setSize(300, 200);    this.setLocationRelativeTo(null);    this.setVisible(true);   }     public static void main(String[] args) {    new Test();   }  }    class ScreenWindow extends JFrame {     private static final long serialVersionUID = -3758062802950480258L;       private boolean isDrag = false;     private int x = 0;     private int y = 0;     private int xEnd = 0;     private int yEnd = 0;     public ScreenWindow(final JLabel imgLabel) throws AWTException, InterruptedException {    Dimension screenDims = Toolkit.getDefaultToolkit().getScreenSize();    JLabel label = new JLabel(new ImageIcon(ScreenImage.getScreenImage(0, 0, screenDims.width, screenDims.height)));    label.setCursor(new Cursor(Cursor.CROSSHAIR_CURSOR));    label.addMouseListener(new MouseAdapter() {     public void mouseClicked(MouseEvent e) {      if (e.getButton() == MouseEvent.BUTTON3) {       dispose();      }     }       public void mousePressed(MouseEvent e) {      x = e.getX();      y = e.getY();     }       public void mouseReleased(MouseEvent e) {      if (isDrag) {       xEnd = e.getX();       yEnd = e.getY();       if(x > xEnd){        int temp = x;        x = xEnd;        xEnd = temp;       }       if(y > yEnd){        int temp = y;        y = yEnd;        yEnd = temp;       }       try {        imgLabel.setIcon(new ImageIcon(ScreenImage.getScreenImage(x, y, xEnd - x, yEnd - y)));       } catch (Exception ex) {        JOptionPane.showConfirmDialog(null, "出现意外错误！", "系统提示", JOptionPane.DEFAULT_OPTION, JOptionPane.ERROR_MESSAGE);       }       dispose();      }     }    });    label.addMouseMotionListener(new MouseMotionListener() {     public void mouseDragged(MouseEvent e) {      if(!isDrag)       isDrag = true;     }       public void mouseMoved(MouseEvent e) {      /** 拖动过程的虚线选取框需自己实现 */     }    });    this.setUndecorated(true);    this.getContentPane().add(label);    this.setSize(screenDims.width, screenDims.height);    this.setVisible(true);    this.setExtendedState(JFrame.MAXIMIZED_BOTH);   }  }    class ScreenImage {     public static Image getScreenImage(int x, int y, int w, int h) throws AWTException, InterruptedException {    Robot robot = new Robot();    Image screen = robot.createScreenCapture(new Rectangle(x, y, w, h)).getScaledInstance(w, h, Image.SCALE_SMOOTH);    MediaTracker tracker = new MediaTracker(new Label());    tracker.addImage(screen, 1);    tracker.waitForID(0);    return screen;   }  }