Set focus on a component with Apache Wicket?

I suggest using the native org.apache.wicket.ajax.AjaxRequestTarget#focusComponent(). For example:

/**
 * Sets the focus in the browser to the given component. The markup id must be set. If            
 * the component is null the focus will not be set to any component.
 * 
 * @param component
 *            The component to get the focus or null.
 */
 org.apache.wicket.ajax.AjaxRequestTarget#focusComponent(Component component)

Once you create your behavior to set the focus, you should be able to add it to the component on any event, just make sure that component is part of the AjaxRequestTarget. I don't see why this wouldn't work...

myRadioButton.add(new AjaxEventBehavior("onchange") {
 @Override
 protected void onEvent(AjaxRequestTarget target) {
    myOtherComponent.add(new DefaultFocusBehavior());
        target.addComponent(myForm);
 }
});

Here's a link that shows how to create the default focus behavior if you do not have one already: http://javathoughts.capesugarbird.com/2009/01/wicket-and-default-focus-behavior.html

If you only want to setFocus through javascript and don't want to reload a form or a component, you can use the following code:

import org.apache.wicket.Component;

public class JavascriptUtils {
    private JavascriptUtils() {

    }

    public static String getFocusScript(Component component) {
        return "document.getElementById('" + component.getMarkupId() + "').focus();";
    }
}

And then in any Ajax Method you can use:

target.appendJavascript(JavascriptUtils.getFocusScript(componentToFocus));