学习springmvc遇到问题请教

我写了一个连接数据库的login.jsp和reg.jsp，成功连接数据库。但是在多次页面转跳后。出现问题
login代码<body>
<h1>欢迎您使用本系统</h1>
      <form action="${path}user/login.do" method="post" >
      输入用户名：<input type="text"  name="user"/><br>
      <p></p>
      输入密码：   <input type="password" name="pwd"/><br>
      <input type = "submit" value="登录"/>
      </form>
</body>
reg代码<body>
      <h1>欢迎注册</h1>
      <form action="reg.do" method="post" >
      输入用户名：<input type="text"  name="user"/><br>
      <p></p>
      输入密码：   <input type="password" name="pwd"/><br>
      <input type = "submit" value="注册"/>
      </form>
</body>
web.xml<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://xmlns.jcp.org/xml/ns/javaee" xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee http://xmlns.jcp.org/xml/ns/javaee/web-app_3_1.xsd" id="WebApp_ID" version="3.1">
  <display-name>mymvc2.0</display-name>
  <welcome-file-list>
    <welcome-file>index.html</welcome-file>
  </welcome-file-list>
  <servlet>
    <servlet-name>mymvc2</servlet-name>
    <servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class>
    <load-on-startup>1</load-on-startup>
  </servlet>
  <servlet-mapping>
    <servlet-name>mymvc2</servlet-name>
    <url-pattern>*.do</url-pattern>
  </servlet-mapping>
  <filter>
    <filter-name>CharacterEncodingFilter</filter-name>
    <filter-class>org.springframework.web.filter.CharacterEncodingFilter</filter-class>
    <init-param>
      <param-name>encoding</param-name>
      <param-value>utf-8</param-value>
    </init-param>
  </filter>
  <filter-mapping>
    <filter-name>CharacterEncodingFilter</filter-name>
    <url-pattern>/*</url-pattern>
  </filter-mapping>
</web-app>
mvc-servelt.xml<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xmlns:context="http://www.springframework.org/schema/context"
xmlns:mvc="http://www.springframework.org/schema/mvc"
xsi:schemaLocation="http://www.springframework.org/schema/mvc http://www.springframework.org/schema/mvc/spring-mvc-3.0.xsd
http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd
http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context-3.0.xsd">     <!--  自动扫描java类，找到那些具备handleAdapter -->
     <context:component-scan base-package="com.zhuquanmin" />
 <mvc:annotation-driven />



   <!-- 支持重定向 -->
    <bean class="org.springframework.web.servlet.view.InternalResourceViewResolver">
           
           <property name="prefix" value="/" />
           <property name="suffix" value=".jsp" />
     </bean>
</beans>
controllerpackage com.zhuquanmin.controller;import java.io.IOException;
import java.util.List;import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;import org.springframework.stereotype.Controller;
import org.springframework.ui.Model;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestParam;
import org.springframework.web.bind.annotation.ResponseBody;
import org.springframework.web.servlet.ModelAndView;import com.zhuquanmin.po.UserInfo;
import com.zhuquanmin.database.QianDBConnection;
import com.zhuquanmin.database.User;@Controller  // 注解形式
@RequestMapping("/user/")
public class UserController {  @RequestMapping("login.do")
public ModelAndView login(HttpServletRequest request,@RequestParam String user,
@RequestParam String pwd) throws IOException
{
   QianDBConnection mdbc = new QianDBConnection();
   String sql="select * from user where account='"+user+"' and password='"+pwd+"'";
   User user1 = new User();
   List list=mdbc.queryByORM(sql, user1);    
   ModelAndView modelAndView=new ModelAndView();
   if(list.size()>0)
   {   
   request.getSession().setAttribute("user", user);
   modelAndView.addObject("userID", user);
   modelAndView.setViewName("success");    
   }
   else
   {
   modelAndView.setViewName("reg");  
   }
   return modelAndView;
}
 
 @RequestMapping("reg.do")
public ModelAndView reg(HttpServletRequest request,@RequestParam String user,
@RequestParam String pwd)
{
   User user1 = new User();
     user1.setAccount(user);
     user1.setPassword(pwd);    
     QianDBConnection mydb=new QianDBConnection();
     mydb.saveByORM(user1);
     ModelAndView modelAndView=new ModelAndView();
     modelAndView.setViewName("login");
     return modelAndView;
}
 
}
出现如下错误：
本应该是这样，但是注册后再登录就变这样无法登陆了