谁能帮我看看这段jsp代码中的问题

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<%@ page contentType="text/html; charset=gb2312" language="java" %>
<%@ page import="java.sql.*" %>
<jsp:useBean class="com.jpkc.users" id="users" scope="page"/>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
  <meta http-equiv="Content-Type" content="text/html; charset=gb2312">
  <title>用户登陆验证</title>
</head>
<body>
<%
  //获取登录的用户名
  String UserName = request.getParameter("UserName");
  //设置users中的UserName变量
  users.setUserName(UserName);
  //获取登录的密码
  String UserPassword = request.getParameter("UserPassword");
  //设置users中的UserPassword变量
  users.setUserPassword(UserPassword);

  //判断用户是否注册
  if(users.is_exist())
  {
   //将用户名和用户编号保存到session中
   session.setAttribute("UserName",UserName);
   session.setAttribute("UserID",users.getUserID()+"");
   //跳转到登录用户主页
   response.sendRedirect("index.html");

  //判断登录的用户名和密码是否正确
  if(users.user_valid())
  {

   //跳转到下载页面
   response.sendRedirect("studydownload.jsp");
  }
  else
  {
%>
   <h2 align="center">您输入的用户名或者密码有误</h2>
   <center>
   <input type="button" name="goback" value="请登录" onClick="javascript:window.history.go(-1)" >
   </center>
<%
  }
%>

<%
  }
  else
  {
%>
   <h2 align="center">请注册</h2>
   <center>
   <input type="button" name="goback" value="返回" onClick="javascript:window.history.go(-1)" >
   </center>
<%
  }
%>

</body>
</html>

在tomcat中运行后出现的问题是

message

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

exception

org.apache.jasper.JasperException: An exception occurred processing JSP page /user_check.jsp at line 3734: {35: 36: //跳转到下载页面37: response.sendRedirect("studydownload.jsp");38: }39: else40: {Stacktrace:org.apache.jasper.servlet.JspServletWrapper.handleJspException(JspServletWrapper.java:551)org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:450)org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:391)org.apache.jasper.servlet.JspServlet.service(JspServlet.java:334)javax.servlet.http.HttpServlet.service(HttpServlet.java:722)

root cause

java.lang.IllegalStateExceptionorg.apache.catalina.connector.ResponseFacade.sendRedirect(ResponseFacade.java:463)org.apache.jsp.user_005fcheck_jsp._jspService(user_005fcheck_jsp.java:98)org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:70)javax.servlet.http.HttpServlet.service(HttpServlet.java:722)org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:417)org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:391)org.apache.jasper.servlet.JspServlet.service(JspServlet.java:334)javax.servlet.http.HttpServlet.service(HttpServlet.java:722)

note The full stack trace of the root cause is available in the Apache Tomcat/7.0.8 logs.