if (callbackHandler == null)
return;
final NameCallback usernameCallback = new NameCallback(USERNAME_PREFIX);
final ObjectCallback passwordCallback = new ObjectCallback();
// Call callback with username and password callbacks
callbackHandler.handle(new Callback[] {usernameCallback, passwordCallback});
username = usernameCallback.getName();
Object o = passwordCallback.getObject();
if (!(o instanceof String))
throw new UnsupportedCallbackException(passwordCallback, Messages.UrlConnectionRetrieveFileTransfer_UnsupportedCallbackException);
password = (String) passwordCallback.getObject();