我想把生成的4位数放在验证码后面的文本框里怎么改

<%@ page language="java" contentType="text/html; charset=UTF-8"
pageEncoding="UTF-8" errorPage="error.jsp"%>
<%@ page import= "edu.jmi.db.*" %>
<%@ page import= "edu.jmi.dao.*" %>
<%@ page import= "java.sql.*" %>

验证码测试登录页面
   <p>


<%
request.setCharacterEncoding("UTF-8");
String name=request.getParameter("name");
String pwss= request.getParameter("password");
if(session.getAttribute("usr")!=null){
response.sendRedirect("main.jsp");
return;
}
if(name!=null){
UserDao ud=new UserDao();
String dbpw=ud.validUser(name);
if(name==null||dbpw==null){
session.setAttribute("echostr", "用户名或密码不能为空，请重新输入");
}else if(dbpw!=null&&dbpw.equals(pwss)){
session.setAttribute("usr", name);
response.sendRedirect("main.jsp");
}else{
session.setAttribute("errmsg", "用户名或密码错，请重新输入");
}
}

  String str =(String)session.getAttribute("echostr");
  if(str==null){   
     str="";
  }
  String err = (String)session.getAttribute("errmsg");
  if(err==null){
      err="";
  }
  Long xx = Math.round(Math.random()*9999);
  while(xx<1000){
   xx = Math.round(Math.random()*9999);
  }

%>
    <div class="container">
        <center>    <h1>登录界面</h1></center>
        <section class="main">
        <p>
        <%=err %>
        <%=str %>
        <%=xx %>
        </p>
        <form class="form-4" method="post">
                 <center>  <tr>
                <td>
                    <label for="name">用户名</label>
                    <input type="txt" name="name" placeholder="name" required>
                </td> <br>
                <br>
               <td>
                    <label for="password">密&nbsp;&nbsp;&nbsp;码</label>
                    <input type="password" name="password" placeholder="password" required > 
               </td><br>
                <br>
                <td>
                    <label for="certCode">验证码</label>
                    <input type="txt" name="certCode" placeholder="certCode" required>
                    <input style="width:50px;background-color:white;color:black" type="text" id="yzphoto" value=""/>
                    <input type="hidden" id="yzm"value="">
                </td> <br>
                <br>
                <td>
                    <input type="submit" name="submit" value="提交">
                </td>
                </tr></center>
            </form>​
        </section>
    </div>
</body>

将验证码传到域里，用EL表达式从域中取出来，放到文本框的value里