在JSP中使用JS表单验证的有关问题

在JSP中使用JS表单验证的问题
我在一个JSP页面中想用JS进行表单验证的时候出错了,能否帮我看一下啊。是一个使用STRUTS标签的JSP页面。本人是新学的,所以可能会出现些很低级的错误,请帮帮忙了

<%@   page   language= "java "   pageEncoding= "GBK "%>
<%@   taglib   uri= "http://jakarta.apache.org/struts/tags-bean "   prefix= "bean "%>  
<%@   taglib   uri= "http://jakarta.apache.org/struts/tags-html "   prefix= "html "%>
 
<html>  
<head>
<title> 用户登陆 </title>

<script   language= "javascript ">
function   checkForm(){
if(document.userlogin.id.value== " ")
{
alert( "请输入身份证号码! ");
document.userlogin.id.focus();
return   false;
}
return   true;
}
</script>  
</head>
<body>
<html:form   action= "/login "   method= "post "   onsubmit= "return   checkForm() "   name= "userlogin ">
<table   border= "2 "   align= "center "   bordercolor= "#000000 "   bgcolor= "#99CCCC ">
<tr>
<td> 身&nbsp;&nbsp;份:   </td>
<td   colspan= "2 ">
<html:select   property= "sf ">
<html:option   key= "----主管---- "   value= "主管 "   />
<html:option   key= "----老师---- "   value= "教师 "   />
<html:option   key= "----同学---- "   value= "学生 "   />
</html:select>
</td>
</tr>
<tr>
<td> 身份证号:   </td>
<td   colspan= "2 "> <html:text   property= "id "/> </td>
</tr>
<tr>
  <td> 密&nbsp;&nbsp;码:   </td>
  <td   colspan= "2 "> <html:password   property= "psw "/> <br> </td>
  </tr>
  <tr>
  <td> 验证码: </td>
  <td> <html:text   property= "randCode "   size= "5 "/> <br> </td>
  <!-- <td> <img   alt= "看不清楚? "   src= "imgcode "   onClick= "this.src= 'imgcode ' "/>
  </td>           -->
  </tr>
  <tr>
            <td   align= "center "     colspan= "3 "> <html:submit   value= "提交 "/>
            &nbsp;&nbsp;&nbsp;&nbsp;
            <html:reset   value= "取消 "/> </td>
        </tr>
    </table>
</html:form>
</body>
</html>

**************************出错提示**************************

type   Exception   report

message  

description   The   server   encountered   an   internal   error   ()   that   prevented   it   from   fulfilling   this   request.

exception