Wicket retrieve javascript variable to use in java

Wicket retrieve javascript variable to use in java

I am trying to retrieve a javascript variable using Java. I think that I
am close to the solution.
I want to retrieve the width of an element on my panel. To achieve this, I
added a behavior to my panel that adds the callback and retrieves the
parameters (width and height).
private class ImageBehavior extends AbstractDefaultAjaxBehavior {
@Override
protected void respond(AjaxRequestTarget target) {
//I receive a JavaScript call :)
StringValue width =
getRequest().getRequestParameters().getParameterValue("width");
StringValue height =
getRequest().getRequestParameters().getParameterValue("height");
}
@Override
protected void updateAjaxAttributes(AjaxRequestAttributes attributes) {
super.updateAjaxAttributes(attributes);
attributes.getExtraParameters().put("width", "undef");
attributes.getExtraParameters().put("height", "undef");
}
@Override
public void renderHead(Component component, IHeaderResponse response) {
super.renderHead(component, response);
response.render(OnDomReadyHeaderItem.forScript(getCallbackScript().toString()));
}
}
In javascript, the following code gets called:
function callbackWicketNewImage(element) {
var wcall = Wicket.Ajax.get({ 'u': 'callbackUrl', 'ep' : {'width':
element.width(), 'height': element.height()}});
}
When the js-code is called, the 'respond' method gets called but the
values of the width and height parameter did not change. They remained
'undef'.