Java ImageIO删除图像后将不释放ram

Question

I have a program that opens some 8k images and resizes them to 200x200 pixels. The program works fine but the problem is it won't free memory after closing each image so it runs out off memory super fast! (after like 40 images)

I have tried flushing and setting image to null, using system.gc(), Also I can't use ImageReader because images aren't formatted properly and says not a jpeg image start with 0x01 0x11 and some other numbers. Also enabling disabling ImageIO.usecatch won't help. I tried to use a global variable for image but it didn't help too.

I need to run program in threads but it uses too much memory even on a single thread after editing some images. I removed extra parts of code that i confirmed have nothing to do with problem.

static public class ImageLoadingTask implements Callable<JPanel> {

        private final URL url;
        private final int i;
        private final JPanel scrollPane;

        ImageLoadingTask(int i, URL url, JPanel scrollPane) {
            this.url = url;
            this.i = i;
            this.scrollPane = scrollPane;
        }

@Override
public JPanel call() {
            try {
                BufferedImage image = ImageIO.read(url);
                ImageIcon icon = new ImageIcon(setImage(image));
                image.flush();
                image = null;
                jPanels[i] = new JPanel();
                jPanels[i].setLayout(new BoxLayout(jPanels[i], 
                          BoxLayout.Y_AXIS));
                JLabel label = new JLabel();
                label.setIcon(icon);
                icon = null;
                jPanels[i].add(label);
                String name = "date";
                if (name.length() > 35) {
                    name = name.substring(0, 32) + "...";
                }
                JLabel jLabel = new JLabel(name);
                jPanels[i].add(jLabel);
                scrollPane.add(jPanels[i]);
                latch.countDown();
                return jPanels[i];
            } catch (Exception ex) {
                ex.printStackTrace();
                latch.countDown();
                demo.infoBox("Failed to open file maybe file is open?",                                                 
                             "Error");
                return new JPanel();
            }

private static Image setImage(BufferedImage source) {
        int height = 150;
        int width = 150;
        if (source.getHeight() / height > source.getWidth() / width) {
            return source.getScaledInstance(source.getWidth() * height / 
            source.getHeight(), height, Image.SCALE_SMOOTH);
        } else {
            return source.getScaledInstance(width, source.getHeight() * width 
            / source.getWidth(), Image.SCALE_SMOOTH);
        }
    }

Answer 1

I think it's likely that getScaledInstance() keeps a reference to the original image that it uses to render the scaled version of that image.

What you should try doing in your setImage() method is creating a new BufferedImage of the desired scaled-down dimensions, then using the createGraphics() method of this new BufferedImage to draw the scaled instance into this new BufferedImage . Then return the new, smaller BufferedImage rather than the scaled instance itself.

You should at that point have a new small image that's free of any references to the original large image, and the original large image will be free to be released by garbage collection.

private static Image setImage(BufferedImage source) {
    int height = 150;
    int width = 150;
    Image scaledImage;

    if (source.getHeight() / height > source.getWidth() / width) {
        width = source.getWidth() * height / source.getHeight();
        scaledImage = source.getScaledInstance(width, height, Image.SCALE_SMOOTH);
    } else {
        height = source.getHeight() * width / source.getWidth();
        scaledImage = source.getScaledInstance(width, height, Image.SCALE_SMOOTH);
    }

    BufferedImage result = new BufferedImage(widht, height, BufferedImage.TYPE_INT_RGB);
    result.createGraphics().drawImage(scaledImage, new AffineTransform(), null);

    return result;
}

Answer 2

I simply opened image with following code and it fixed my problem!

Toolkit toolkit = Toolkit.getDefaultToolkit(); Image image = toolkit.getImage(url.getPath());