java – 制作jfilechooser显示图像缩略图

public static void main(String[] args) { 
    JFileChooser chooser=new JFileChooser();
    ThumbNailView thumbView=new ThumbNailView();
    chooser.setFileView(thumbView);
  }

class ThumbNailView extends FileView{
 public Icon getIcon(File f){
  Icon icon=null;
  if(isImageFile(f.getPath())){
   icon=createImageIcon(f.getPath(),null);
  }
  return icon;
 }
 private ImageIcon createImageIcon(String path,String description) {
  if (path != null) {
   ImageIcon icon=new ImageIcon(path);
   Image img = icon.getImage() ; 
   Image newimg = img.getScaledInstance( 16,16,java.awt.Image.SCALE_SMOOTH ) ;
   return new ImageIcon(newimg);
  } else {
   System.err.println("Couldn't find file: " + path);
   return null;
   }
}

private boolean isImageFile(String filename){
    //return true if this is image
}

尽管使用原生的外观和放大器,我还是很惊讶地看到了这一点.感觉在Windows中,文件选择器确实没有缩略图视图.我尝试了你的例子,你沿着正确的方向前进,但我看到有很多大图像的文件夹有多慢.当然,开销是由于读取文件内容然后解释图像时的I / O,这是不可避免的.

更糟糕的是,我发现FileView.getIcon(File)被大量调用 – 在显示文件列表之前,当鼠标悬停在图标上以及选择更改时.如果我们在加载后不缓存图像,我们将无意义地重新加载图像.

显而易见的解决方案是将所有图像加载推送到另一个线程或线程池,一旦我们得到缩小的结果,将其放入临时缓存中,以便可以再次检索它.

我经常使用Image和ImageIcon,我发现可以通过调用setImage(Image)随时更改ImageIcon的图像.这对我们来说意味着,在getIcon(File)中,我们可以立即返回一个空白或默认图标,但保留对它的引用,将其传递给工作线程,该工作线程将在后台加载图像并设置图标的图像后来当它完成时(唯一的问题是我们必须调用repaint()来查看更改).

对于此示例,我使用的是ExecutorService缓存线程池(这是获取所有图像的最快方法,但使用大量I / O)来处理图像加载任务.我也使用WeakHashMap作为缓存,以确保只要我们需要它们就只保留缓存的图标.您可以使用其他类型的Map,但是您必须管理您保留的图标数量,以避免内存不足.

package guitest;

import java.awt.Image;
import java.awt.image.BufferedImage;
import java.io.File;
import java.util.Map;
import java.util.WeakHashMap;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.regex.Pattern;

import javax.swing.Icon;
import javax.swing.ImageIcon;
import javax.swing.JFileChooser;
import javax.swing.SwingUtilities;
import javax.swing.UIManager;
import javax.swing.filechooser.FileView;

public class ThumbnailFileChooser extends JFileChooser {

    /** All preview icons will be this width and height */
    private static final int ICON_SIZE = 16;

    /** This blank icon will be used while previews are loading */
    private static final Image LOADING_IMAGE = new BufferedImage(ICON_SIZE,ICON_SIZE,BufferedImage.TYPE_INT_ARGB);

    /** Edit this to determine what file types will be previewed. */
    private final Pattern imageFilePattern = Pattern.compile(".+?.(png|jpe?g|gif|tiff?)$",Pattern.CASE_INSENSITIVE);

    /** Use a weak hash map to cache images until the next garbage collection (saves memory) */
    private final Map imageCache = new WeakHashMap();

    public static void main(String[] args) throws Exception {
        UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
        JFileChooser chooser = new ThumbnailFileChooser();
        chooser.showOpenDialog(null);
        System.exit(1);
    }

    public ThumbnailFileChooser() {
        super();
    }

    // --- Override the other constructors as needed ---

    {
        // This initializer block is always executed after any constructor call.
        setFileView(new ThumbnailView());
    }

    private class ThumbnailView extends FileView {
        /** This thread pool is where the thumnnail icon loaders run */
        private final ExecutorService executor = Executors.newCachedThreadPool();

        public Icon getIcon(File file) {
            if (!imageFilePattern.matcher(file.getName()).matches()) {
                return null;
            }

            // Our cache makes browsing back and forth lightning-fast! :D
            synchronized (imageCache) {
                ImageIcon icon = imageCache.get(file);

                if (icon == null) {
                    // Create a new icon with the default image
                    icon = new ImageIcon(LOADING_IMAGE);

                    // Add to the cache
                    imageCache.put(file,icon);

                    // Submit a new task to load the image and update the icon
                    executor.submit(new ThumbnailIconLoader(icon,file));
                }

                return icon;
            }
        }
    }

    private class ThumbnailIconLoader implements Runnable {
        private final ImageIcon icon;
        private final File file;

        public ThumbnailIconLoader(ImageIcon i,File f) {
            icon = i;
            file = f;
        }

        public void run() {
            System.out.println("Loading image: " + file);

            // Load and scale the image down,then replace the icon's old image with the new one.
            ImageIcon newIcon = new ImageIcon(file.getAbsolutePath());
            Image img = newIcon.getImage().getScaledInstance(ICON_SIZE,Image.SCALE_SMOOTH);
            icon.setImage(img);

            // Repaint the dialog so we see the new icon.
            SwingUtilities.invokeLater(new Runnable() {public void run() {repaint();}});
        }
    }

}

已知的问题：

1)缩放时我们不保持图像的宽高比.这样做可能会导致图标具有奇怪的尺寸,从而破坏列表视图的对齐方式.解决方案可能是创建一个16×16的新BufferedImage,并在其上方渲染缩放图像,居中.如果你愿意,你可以实现！

2)如果文件不是图像或已损坏,则根本不会显示任何图标.看起来程序只在渲染图像时检测到这个错误,而不是在我们加载或缩放它时,所以我们无法提前检测到.但是,如果我们解决问题1,我们可能会检测到它.