Serverside thread to refresh an image

Flow
1

I would like to have a Java Timer to update an image if a CheckBox is selected.

Checkbox refresh = new Checkbox("Automatic refresh");
Image image = new Image();
add(refresh, image);

Timer timer = new Timer("CameraUpdate");
timer.schedule(new ImageUpdate(), 0, 5000);

private class ImageUpdate extends TimerTask {
    @Override
    public void run() {
        try {
            getUI().get().access(() -> {
                image.setSrc("http://source/img.jpg?timestamp=" + System.currentTimeMillis());
            });
        } catch (Exception ex) {
            logger.error("Can't update image: {}", ex.getMessage());
        }
    }
}

But an error is thrown within the run. I think because there is no link between the Thread and the image.
How can this be done?

Thanks
Frank

2

Hi Frank,

You should capture the UI outside the body of run method; a solution may be using Attach/Detach event listener to capture UI, schedule and cancel the Timer.

Checkbox refresh = new Checkbox("Automatic refresh");
Image image = new Image();
add(refresh, image);

Timer timer = new Timer("CameraUpdate");

addAttachListener(event -> {
	UI ui = event.getUI();	
	timer.schedule(new ImageUpdate(ui), 0, 5000);	
});
addDetachListener(event -> timer.cancel());


private class ImageUpdate extends TimerTask {
    private final UI ui;
	ImageUpdate(UI ui) { this.ui = ui; }
    @Override
    public void run() {
        try {
            ui.access(() -> {
                image.setSrc("http://source/img.jpg?timestamp=" + System.currentTimeMillis());
            });
        } catch (Exception ex) {
            logger.error("Can't update image: {}", ex.getMessage());
        }
    }
}

HTH

Marco

3

Seems to be a perfect solution, thanks a lot Marco!