项目要用，网上找的
  1 package ImageAPI;
  2 import javax.swing.*;
  3 import java.awt.*;
  4 import java.awt.event.*;
  5 import java.beans.*;
  6 import java.io.File;
  7 
  8 /**
  9  * @author matthew
 10  * 
 11  */
 12 public class ImagePreviewPanel extends JPanel implements PropertyChangeListener {
 13 
 14     private int width, height;
 15 
 16     private ImageIcon icon;
 17 
 18     private Image image;
 19 
 20     private static final int ACCSIZE = 155;
 21 
 22     private Color bg;
 23 
 24     public ImagePreviewPanel() {
 25         setPreferredSize(new Dimension(ACCSIZE, -1));
 26         bg = getBackground();
 27     }
 28 
 29     public void propertyChange(PropertyChangeEvent e) {
 30         String propertyName = e.getPropertyName();
 31 
 32         // Make sure we are responding to the right event.
 33         if (propertyName.equals(JFileChooser.SELECTED_FILE_CHANGED_PROPERTY)) {
 34             File selection = (File) e.getNewValue();
 35             String name;
 36 
 37             if (selection == null)
 38                 return;
 39             else
 40                 name = selection.getAbsolutePath();
 41 
 42             /*
 43              * Make reasonably sure we have an image format that AWT can handle
 44              * so we don't try to draw something silly.
 45              */
 46             if ((name != null) && name.toLowerCase().endsWith(".jpg")
 47                     || name.toLowerCase().endsWith(".jpeg")
 48                     || name.toLowerCase().endsWith(".gif")
 49                     || name.toLowerCase().endsWith(".png")) {
 50                 icon = new ImageIcon(name);
 51                 image = icon.getImage();
 52                 scaleImage();
 53                 repaint();
 54             }
 55         }
 56     }
 57 
 58     private void scaleImage() {
 59         width = image.getWidth(this);
 60         height = image.getHeight(this);
 61         double ratio = 1.0;
 62 
 63         /*
 64          * Determine how to scale the image. Since the accessory can expand
 65          * vertically make sure we don't go larger than 150 when scaling
 66          * vertically.
 67          */
 68         if (width >= height) {
 69             ratio = (double) (ACCSIZE - 5) / width;
 70             width = ACCSIZE - 5;
 71             height = (int) (height * ratio);
 72         } else {
 73             if (getHeight() > 150) {
 74                 ratio = (double) (ACCSIZE - 5) / height;
 75                 height = ACCSIZE - 5;
 76                 width = (int) (width * ratio);
 77             } else {
 78                 ratio = (double) getHeight() / height;
 79                 height = getHeight();
 80                 width = (int) (width * ratio);
 81             }
 82         }
 83 
 84         image = image.getScaledInstance(width, height, Image.SCALE_DEFAULT);
 85     }
 86 
 87     public void paintComponent(Graphics g) {
 88         g.setColor(bg);
 89 
 90         /*
 91          * If we don't do this, we will end up with garbage from previous images
 92          * if they have larger sizes than the one we are currently drawing.
 93          * Also, it seems that the file list can paint outside of its rectangle,
 94          * and will cause odd behavior if we don't clear or fill the rectangle
 95          * for the accessory before drawing. This might be a bug in
 96          * JFileChooser.
 97          */
 98         g.fillRect(0, 0, ACCSIZE, getHeight());
 99         g.drawImage(image, getWidth() / 2 - width / 2 + 5, getHeight() / 2
100                 - height / 2, this);
101     }
102 
103     /**
104      * @param args
105      */
106     public static void main(String[] args) {
107         JFileChooser chooser = new JFileChooser();
108         ImagePreviewPanel preview = new ImagePreviewPanel();
109         chooser.setAccessory(preview);
110         chooser.addPropertyChangeListener(preview);
111         chooser.showOpenDialog(null);
112 
113     }
114 
115 }