java - How to dynamically check existing user in wicket -

in web application have register form new user. there 1 field username:

    textfield<string> username = new textfield<string>("username");     username.add(usernamevalidator.getinstance()); 

when user push button username validate. behaviour not user friendly. there options how validate dynamically , if there error in validation user cant push button ?

you can use the: onchangeajaxbehavior

  username.add(new onchangeajaxbehavior() {       @override      protected void onupdate(ajaxrequesttarget target) {         //do stuff here      }   });