Minor Description
To demonstrate the issue, create below simple page:
"HomePage.html"
<wicket:extend>
<select wicket:id="choice"></select>
</wicket:extend>
"HomePage.java"
public class HomePage extends WebPage { private String choice = "a"; @Override protected void onInitialize() { super.onInitialize(); List<String> choices = new ArrayList<String>(); choices.add("a"); choices.add("b"); add(new DropDownChoice<String>("choice", new IModel<String>() { @Override public void detach() { } @Override public String getObject() { return choice; } @Override public void setObject(String object) { choice = object; } }, choices).add(new OnChangeAjaxBehavior() { @Override protected void onUpdate(AjaxRequestTarget target) { System.out.println(choice); } })); } }
This simple page prints out choosed value via OnChangeAjaxBehavior, it works fine if you access the page via http://localhost:8080. However it always prints "null" if you access the page with a request parameter the same name as the wicket id, for instance: http://localhost:8080/?choice=somevalue
It works again if you use different value for wicket id of the choice component and request parameter.