帮忙下怎么把验证码传到后台做判断

package com.sorfteem.informationsystem.until;import java.io.IOException;
import java.io.PrintWriter;import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;public class CheckNumber extends HttpServlet {
public void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
        doPost(request,response);

} public void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
             HttpSession session=request.getSession();
             if (session!=null) {
String myrnd=RndImage.random();
System.out.println(myrnd);
session.setAttribute("rnd", myrnd);
response.setContentType("image/jpeg");
response.setContentType("rnd");
RndImage.ImageOut(myrnd,response.getOutputStream(),80,20);
}

}}
 ？？？？这个里面的session.setAttribute("rnd", myrnd); 的rnd 传到下面的 WelcomeServlet 里面么 ？如果能 该怎么判断 rnd 的值和code 的值是否相等，同时 login》jsp里的    <input type="hidden" name="rnd" value='<%=session.getAttribute("rnd") %>+"@@@@@@"'/> 这句话是否可以省略。
lcom.sorfteem.informationsystem.welcomeservlet;import java.io.IOException;import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;import com.sorfteem.informationsystem.dao.UserDAO;
import com.sorfteem.informationsystem.dto.UserDTO;public class WelcomeServlet extends HttpServlet { @Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp)
throws ServletException, IOException {
// TODO Auto-generated method stub
doPost(req, resp);
} @Override
protected void doPost(HttpServletRequest req, HttpServletResponse resp)
throws ServletException, IOException {
// TODO Auto-generated method stub
req.setCharacterEncoding("utf-8");
String name=req.getParameter("username");
String password=req.getParameter("password");
String code=req.getParameter("code");
String rnd = req.getParameter("rnd");
UserDTO dto=new UserDTO(name,password);
UserDAO  dao=new UserDAO();
UserDTO flag=dao.validate(dto);
System.out.println("code:+++"+code);
System.out.println("rnd:+++"+rnd);
if (flag!=null&&code.equalsIgnoreCase(rnd)) {

HttpSession session=req.getSession();
session.setAttribute("isUser", flag);
    session.getAttribute("rnd");
    System.out.println( session.getAttribute("rnd")+"222222222");
System.out.println(((UserDTO)session.getAttribute("isUser")).getId());
req.getRequestDispatcher("welcome.jsp").forward(req, resp);

}else{
resp.sendRedirect("login.jsp");
}
}
  
}
login.jsp 页面
<%@ page language="java" pageEncoding="UTF-8"%>
<%@ taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c" %>
<%
String path = request.getContextPath();
String basePath = request.getScheme() + "://"
+ request.getServerName() + ":" + request.getServerPort()
+ path + "/";
%>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<head>
<base href="<%=basePath%>"> <title>企业信息管理系统 - 登录</title> <meta http-equiv="pragma" content="no-cache">
<meta http-equiv="cache-control" content="no-cache">
<meta http-equiv="expires" content="0">
<meta http-equiv="keywords" content="企业,信息,管理">
<meta http-equiv="description" content="企业信息管理系统 - 登录窗口">
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<link rel="stylesheet" type="text/css" href="css/styles.css">
<script language="javascript">
function validLogin(theform) {
var username = theform.username.value;
var password = theform.password.value;
var code=theform.code.value;
if (username == "") {
    alert("用户名不能为空！");
return false;
}
if (password == "") {
    alert("密码不能为空！");
return false;
}
if(code == ""){
alert("验证码！");
return false;
}
return true;
}
</script>
</head>
<body bgcolor="#52BDFE">
<table height="100%" width="100%">
<tr>
<td align="center">
<table width="572" height="307" background="images/login.jpg">
<tr>
<td width="60%"></td>
<td>
<form name="form1" action="WelcomeServlet" method="post"
onsubmit="return validLogin(this);">
<table>
<tr>
<td>
用户名：
</td>
<td>
<input type="text" name="username" size="10">
</td>
</tr>
<tr>
<td>
密&nbsp;&nbsp;码：
</td>
<td>
<input type="password" name="password" size="10">
</td>
</tr>
<tr>
<td>
<img id="rnd" src="/InformationSystem/CheckNumber" border="0"/>
</td>
<td>

         <input type="hidden" name="rnd" value='<%=session.getAttribute("rnd") %>+"@@@@@@"'/>
<input name="code" type="text" size="4" />
</td>
</tr>
<tr>
<td colspan="2">
<a href="register.jsp">注册新用户</a>
<input type="submit" name="submit" value="登录系统">
</td>
</tr> </table>
</form>
</td>
</tr>
</table>
</td>
</tr>
</table>
</body>
</html>