在JLabel上显示图片，并且图片自适应JLabel的大小

本文转载地址：

      http://blog.csdn.net/xiaoliangmeiny/article/details/7060250

---

      在写《Core Java》上的示例代码时，其中有一个FileChooserTest是打开一张图片，并在Label上显示出来，但是这个示例程序有缺点，由于窗口的大小已经固定，而选择打开的图片有大有小，如果图片比窗口大，则超过框口部分的则被隐藏没显示出来，要靠拖动窗口才能显示其余部分，若图片比较小，则打开在窗口中显得过小，于是稍作了修改。使得打开的图片可以完全根据窗口大小调整自身大小，也可以根据窗口的宽等比缩放。由于之前在网上搜索发现不少人遇到同样的问题，且大都没有有效解决掉，故把代码贴出来：

package FileChooserTest;

import java.awt.BorderLayout;
import java.awt.Dimension;
import java.awt.EventQueue;
import java.awt.Image;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.beans.PropertyChangeEvent;
import java.beans.PropertyChangeListener;
import java.io.File;

import javax.swing.BorderFactory;
import javax.swing.Icon;
import javax.swing.ImageIcon;
import javax.swing.JFileChooser;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JMenu;
import javax.swing.JMenuBar;
import javax.swing.JMenuItem;
import javax.swing.SwingConstants;
import javax.swing.UIManager;
import javax.swing.UnsupportedLookAndFeelException;
import javax.swing.filechooser.FileFilter;
import javax.swing.filechooser.FileNameExtensionFilter;
import javax.swing.filechooser.FileView;

public class FileChooserTest {

    public static void main(String[] args) {
        EventQueue.invokeLater(new Runnable() {
            public void run() {
                ImageViewerFrame frame = new ImageViewerFrame();
                frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
                frame.setVisible(true);
            }
        });
    }
}

class ImageViewerFrame extends JFrame {

    public ImageViewerFrame() {
        super("ImageViewer");
        setSize(WIDTH, HEIGHT);
        try {
            UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
        } catch (Exception e) {
            //
        }

        JMenuBar menuBar = new JMenuBar();
        setJMenuBar(menuBar);
        JMenu menu = new JMenu("File");
        JMenuItem openItem = new JMenuItem("open");
        menu.add(openItem);
        openItem.addActionListener(new FileOpenListener());
        JMenuItem exitItem = new JMenuItem("exit");
        menu.add(exitItem);
        menuBar.add(menu);
        exitItem.addActionListener(new ActionListener() {
            public void actionPerformed(ActionEvent e) {
                // TODO Auto-generated method stub
                System.exit(0);
            }
        });

        //use a label to display a image
        label =new JLabel();
        add(label,BorderLayout.CENTER);

        chooser=new JFileChooser();
        FileNameExtensionFilter filter =new FileNameExtensionFilter("Image Files", "jpg","jpeg","gif");
        chooser.setFileFilter(filter);
        //预览
        chooser.setAccessory(new ImagePreviewer(chooser));
        //accessory 通常用于显示已选中文件的预览图像

//      chooser.setFileView(new FileIconView(filter,new ImageIcon("palette.gif")));
        chooser.setFileView(new FileIconView(filter, new ImageIcon()));
        //设置用于检索 UI 信息的文件视图，如表示文件的图标或文件的类型描述。

    }

    private class FileOpenListener implements ActionListener{
        @Override
        public void actionPerformed(ActionEvent e) {
            // TODO Auto-generated method stub
            chooser.setCurrentDirectory(new File("."));
            int result=chooser.showOpenDialog(ImageViewerFrame.this);
            if(result==JFileChooser.APPROVE_OPTION){
                String name=chooser.getSelectedFile().getPath();
                ImageIcon icon=new ImageIcon(name);
//              等比缩放条件
//              int imgWidth=icon.getIconWidth();
//              int imgHeight=icon.getIconHeight();
//              int conWidth=getWidth();
//              int conHeight=getHeight();
//              int reImgWidth;
//              int reImgHeight;
//              if(imgWidth/imgHeight>=conWidth/conHeight){
//                  if(imgWidth>conWidth){
//                      reImgWidth=conWidth;
//                      reImgHeight=imgHeight*reImgWidth/imgWidth;
//                  }else{
//                      reImgWidth=imgWidth;
//                      reImgHeight=imgHeight;
//                  }
//              }else{
//                  if(imgWidth>conWidth){
//                      reImgHeight=conHeight;
//                      reImgWidth=imgWidth*reImgHeight/imgHeight;
//                  }else{
//                      reImgWidth=imgWidth;
//                      reImgHeight=imgHeight;
//                  }
//              }
                //这个是强制缩放到与组件(Label)大小相同
                icon=new ImageIcon(icon.getImage().getScaledInstance(getWidth(), getHeight()-25, Image.SCALE_DEFAULT));
                //这个是按等比缩放
//              icon=new ImageIcon(icon.getImage().getScaledInstance(reImgWidth, reImgHeight, Image.SCALE_DEFAULT));
                label.setIcon(icon);
                label.setHorizontalAlignment(SwingConstants.CENTER);
            }
        }
    }

    public static final int WIDTH = 500;
    public static final int HEIGHT = 500;

    private JLabel label;
    private JFileChooser chooser;
}

class FileIconView extends FileView {
    public FileIconView(FileFilter aFilter,Icon anIcon){
        filter=aFilter;
        icon=anIcon;
    }
    public Icon getIcon(File f){
        if(!f.isDirectory()&&filter.accept(f)){
            return icon;
        }else return null;
    }
    private FileFilter filter;
    private Icon icon;
}

class ImagePreviewer extends JLabel{
    public ImagePreviewer(JFileChooser chooser){
        setPreferredSize(new Dimension(100,100));
        setBorder(BorderFactory.createEtchedBorder());
        chooser.addPropertyChangeListener(new PropertyChangeListener() {
            public void propertyChange(PropertyChangeEvent event) {
                if(event.getPropertyName()==JFileChooser.SELECTED_FILE_CHANGED_PROPERTY){
                    File f=(File) event.getNewValue();
                    if(f==null){
                        setIcon(null);
                        return;
                    }
                    ImageIcon icon=new ImageIcon(f.getPath());
//                  if(icon.getIconWidth()>getWidth()){
                        icon=new ImageIcon(icon.getImage().getScaledInstance(getWidth(), -1, Image.SCALE_DEFAULT));
//                  }
                    setIcon(icon);
                }
            }
        });
    }
}

 选择等比缩放还是完全自适应，看代码注释处切换。