html:select onchange

[struts]

Problem how can i pass the userId ? so that i can do a request.getParameter("userId")  
?

example:



<html:select property="users.userAccount" 
onchange="setAction('setUpUsersForm.do?action=retrieve&userId=" >

<html:options labelProperty="userName" collection="userList" property="userId" />

</html:select> 





Thanks !