高手进，servlet+jsp编程报错

写的一程序行通过servlet从数据库中取出数据，然后用jsp显示数据，但是页面报错：
org.apache.jasper.JasperException: An exception occurred processing JSP page /liststu.jsp at line 1310:     <table align="center" border="1">
11:     <tr><td>id</td><td>name</td><td>age</td><td>salary</td></tr>
12:     <%List<Student> list=(List<Student>)request.getAttribute("student");
13:     for(int i=0;i<list.size();i++){Student stu=list.get(i);%>
14:     <tr><td><%=stu.getId()%></td><td><%=stu.getName()%></td>
15:     <td><%=stu.getAge()%></td><td><%=stu.getSalary() %></td></tr>
16:     <%}%>
Stacktrace:
org.apache.jasper.servlet.JspServletWrapper.handleJspException(JspServletWrapper.java:510)
org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:419)
org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:313)
org.apache.jasper.servlet.JspServlet.service(JspServlet.java:260)
javax.servlet.http.HttpServlet.service(HttpServlet.java:717)
root cause java.lang.NullPointerException
org.apache.jsp.liststu_jsp._jspService(liststu_jsp.java:68)
org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:70)
javax.servlet.http.HttpServlet.service(HttpServlet.java:717)
org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:377)
org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:313)
org.apache.jasper.servlet.JspServlet.service(JspServlet.java:260)
javax.servlet.http.HttpServlet.service(HttpServlet.java:717)具体的代码如下：
servlet代码
   package com.koncord;import java.io.IOException;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.util.ArrayList;
import java.util.List;import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;public class ListStuServlet extends HttpServlet { public void service(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
String url="jdbc:mysql://127.0.0.1:3306/temp";
String driverName="com.mysql.jdbc.Driver";
String username="root";
String password="koncord";
List<Student>student=new ArrayList<Student>();
try{
Connection con=null;
PreparedStatement ps=null;
ResultSet rs=null;
Class.forName(driverName);
con=DriverManager.getConnection(url,username,password);
String sql="select *from student";
ps=con.prepareStatement(sql);
rs=ps.executeQuery();
while(rs.next()){
Student s=new Student(rs.getInt("id"),rs.getString("name"),rs.getInt("age"),rs.getDouble("salary"));
student.add(s);
System.out.println(student.size());
}

request.setAttribute("student", student);
request.getRequestDispatcher("liststu.jsp").forward(request, response);
}catch(Exception e){
e.printStackTrace();
}
}}
jsp页面代码 <%@page language="java" import="java.util.*,com.koncord.Student" pageEncoding="utf-8"%>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
  <head>
    <title>学生信息</title>
  </head>
  
  <body>
   <div align="center">
    <table align="center" border="1">
    <tr><td>id</td><td>name</td><td>age</td><td>salary</td></tr>
    <%List<Student> list=(List<Student>)request.getAttribute("student");
    for(int i=0;i<list.size();i++){Student stu=list.get(i);%>
    <tr><td><%=stu.getId()%></td><td><%=stu.getName()%></td>
    <td><%=stu.getAge()%></td><td><%=stu.getSalary() %></td></tr>
    <%}%>
    </table>
    </div>
  </body>
</html>