Loading large images as thumbnails without memory issues in Java?

Question

I\'m trying to let the user load images from their harddrive, and present these visually in the GUI as a list of thumbnails (JPanels with icons added to a JList). I\'m curre

Answer 1

The JVM has a nasty habit of caching images. One way to get around it is to:

1. Create an InputStream pointing to the image.
2. Read the entire image data into a byte[] (using standard I/O APIs - outside imageio etc.).
3. Create a ByteArrayInputStream from the byte[].
4. Use the ByteArrayInputStream as a source for ImageIO.read(InputStream).

Because the JVM does not know from what resource the image bytes were obtained it is unable to uniquely identify the image, and will not cache it.

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Mind you, I cannot find any documentation that backs up what I am saying. This is just from past experience.

Answer 2

The problem is in the use of BufferedImage itself. By the time the file is read into memory you'll be out of heap space. Depending on what this is for you can either use an image reader or you can increase the size of the heap.

I'd recommend that you use an image reader. For example to get an image reader you code would be something like this:

  // Create an image input stream on the image
    ImageInputStream iis = ImageIO.createImageInputStream(o);

    // Find all image readers that recognize the image format
    Iterator iter = ImageIO.getImageReaders(iis);
    if (!iter.hasNext()) {
        // No readers found
        return null;
    }

    // Use the first reader
    ImageReader reader = (ImageReader)iter.next();

From : http://www.exampledepot.com/egs/javax.imageio/DiscType.html

One you have the ImageReader you can get the aspect ration by calling reader.getAspectRatio()

I'm not sure how you'd go from an ImageReader to a thumbnail though.