使jfilechooser显示图像缩略图 [英] making jfilechooser show image thumbnails
问题描述
我想创建一个 JFileChooser ，其中包含图像文件的缩略图视图。所以我将FileView和创建 ImageIcon 做了一些缩放图像显示缩略图。
I wanted to create a JFileChooser with thumbnail view of image files.So I subclassed FileView and in the method which creates ImageIcon did some scaling sothat thumbnail images are shown.
然而，总体效果是， filechooser widget在打开目录并显示缩略图之前需要一些时间。在下面的createImageIcon（）中，我需要使用图像文件路径两次调用新的ImageIcon（），然后使用调整大小的图像作为构造函数参数。我认为这是慢的小部件。
However,the overall effect is that, the filechooser widget takes some time before opening a directory and showing thumbnails..In createImageIcon() below,I need to call new ImageIcon() twice-once with the image filepath and next with the resized image as constructor argument.I think this is what slows the widget .
是否有更有效的替代方案？欢迎任何建议/指示。
Is there a more efficient alternative?Any suggestions/pointers most welcome.
谢谢，
mark
thanks, mark
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
}
推荐答案
我真的很惊讶地看到，尽管使用原生的外观&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。
I was actually surprised to see that, despite using the native look & feel in Windows, the file chooser indeed doesn't have a thumbnail view. I tried your example and you're going along the right lines, but I see how slow it was for folders with a lot of large images. The overhead is, of course, due to I/O when reading the file contents and then interpreting the image, which is unavoidable.
更糟糕的是，我找到了出现 FileView.getIcon（文件）被称为批次 - 在显示文件列表之前，当鼠标悬停在图标上时，以及选择变化。如果我们在加载后没有缓存图像，我们将毫无意义地重新加载图像。
What's even worse, is that I found out that FileView.getIcon(File) is called a lot - before the file list is shown, when you mouse over an icon, and when the selection changes. If we don't cache the images after loading them, we'll be pointlessly reloading images all the time.
显而易见的解决方案是将所有图像加载到另一个线程或一个线程池，一旦我们得到缩小的结果，就把它放到一个临时缓存中，这样就可以再次检索它。
The obvious solution is to push all the image loading off onto another thread or a thread pool, and once we have our scaled-down result, put it into a temporary cache so it can be retrieved again.
我玩了图片和 ImageIcon 很多，我发现 ImageIcon '可以通过调用 setImage（Image）随时更改图像。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这将在后台加载图像并在完成后设置图标的图像（唯一的问题是我们必须调用 repaint（）来查看更改）。
I played around with Image and ImageIcon a lot and I discovered that an ImageIcon's image can be changed at any time by calling setImage(Image). What this means for us is, within getIcon(File), we can immediately return a blank or default icon, but keep a reference to it, passing it along to a worker thread that will load the image in the background and set the icon's image later when it's done (The only catch is that we must call repaint() to see the change).
对于这个例子，我使用的是一个 ExecutorService 缓存的线程池（这是获取所有图像的最快方法，但是使用了大量的I / O来处理图像加载任务。我还使用 WeakHashMap 作为缓存，以确保只要我们需要它们，我们只保留缓存的图标。你可以使用另一种地图，但你必须管理你所持有的图标数量，以避免内存不足。
For this example, I'm using an ExecutorService cached thread pool (this is the fastest way to get all images, but uses a lot of I/O) to process the image loading tasks. I'm also using a WeakHashMap as the cache, to ensure that we only hold onto the cached icons for as long as we need them. You could use another kind of Map, but you would have to manage the number of icons you hold onto, to avoid running out of memory.
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, 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16x16的新 BufferedImage 并在其上方渲染缩放图像，居中。如果你愿意，你可以实现它！
1) We don't maintain the image's aspect ratio when scaling. Doing so could result in icons with strange dimensions that will break the alignment of the list view. The solution is probably to create a new BufferedImage that is 16x16 and render the scaled image on top of it, centered. You can implement that if you wish!
2）如果文件不是图像，或者已损坏，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，如果我们修复问题1，我们可能会检测到它。
2) If a file is not an image, or is corrupted, no icon will be shown at all. It looks like the program only detects this error while rendering the image, not when we load or scale it, so we can't detect this in advance. However, we might detect it if we fix issue 1.
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