ext表单中的值request.getParameter("id")始终得不到

ext部分代码：
if (formPanel.getForm().isValid()) {

        formPanel.getForm().submit({
            clientValidation: true,

            url: 'servlet/AddUser',
            //method : 'post', 
            params:{
                id:formPanel.getForm().findField('id').getValue(),
                name:formPanel.getForm().findField('name').getValue(),
                userName:formPanel.getForm().findField('userName').getValue(),
                department:formPanel.getForm().findField('department').getValue(),
                groups_id:formPanel.getForm().findField('Group_id').getValue()
            },


            success: function(form, action) {

后台java部分代码：
public void service(HttpServletRequest request ,
HttpServletResponse response)
throws IOException , ServletException
{
Map map = new HashMap();
final Log log = LogFactory.getLog(UserDAO.class);
try {
request.setCharacterEncoding("utf-8");
String id = request.getParameter("id");
String name = request.getParameter("name");
String userName = request.getParameter("userName");
String department = request.getParameter("department");
String groups_id = request.getParameter("Group_id");
System.out.println(userName);//都是null
System.out.println(name);//都是null
怎么也得不到前台表单的值，请高手指点一二，不胜感激