From http://www.dreamincode.net/forums/topic/162999-java-image-manipulation-part-3-math-and-swingworker/ Loading image Asynchron

WebScanner.java

public class WebScanner {
    
    // These are the variables that hold the URL and the 
    // image when done loading
    private BufferedImage img;
    private URL url;
    
    // This is a bit more complicated, but I explained it above.
    private SwingWorker<BufferedImage, Void> worker = new SwingWorker<BufferedImage, Void>() {
        @Override
        public BufferedImage doInBackground() {
            BufferedImage image = null;
            try {
                image = ImageIO.read(url);
            } catch (IOException e) {
                System.err.println("A loading error occurred");
            }
            return image;
        }

        @Override
        public void done() {
            try {
                img = get();
            } catch (InterruptedException ignore) {}
            catch (ExecutionException e) {
                String why = null;
                Throwable cause = e.getCause();
                if (cause != null) {
                    why = cause.getMessage();
                } else {
                    why = e.getMessage();
                }
                System.err.println("A loading error occurred: " + why);
            }
        }
    };
    
    // Sets the URL. Again...using an astronomy picture...
    public void setURL() {
        try {
            url = new URL("http://antwrp.gsfc.nasa.gov/apod/image/1003/mb_2010-03-10_SeaGullThor.jpg");
        } catch (MalformedURLException e) {
            System.err.println("Your tutorial writer wrote down the wrong internet address");
        }
    }
    
    // This returns the image when done loading. If there is
    // a null image, then we retry.
    public BufferedImage getImage(String fn) {
        if (img == null) {
            System.err.println("Attempting again");
            // Starts the worker
            worker.execute();
        }
        return img;
    }
    
    // Access to the worker
    public void startWorker() {
        // Starts the worker
        worker.execute();
    }
    
    public boolean isWorkerDone() { 
        return worker.isDone();
    }
    
}