求助！！ecplise中出现 Description The origin server did not find a current representati - 编程论坛

刚开始学习有关java web的内容，在联系连接MySQL数据库，然后实现简单的登录页面，但是页面跳转不了，请问这是什么原因，哪个大神能来指点一下！！！
===============================================================================================================
<%@ page language="java" contentType="text/html; charset=UTF-8"
    pageEncoding="UTF-8"%>
<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title>Insert title here</title>
</head>
<body>
    <form action="DengLuServlet" method="post">
        <input type="text" name="sname" /><br/>
        <input type="password" name="spwd" "/><br/>
        <input type="submit" value="登录"/>
    </form>
</html>
==========================================================================================================

DengLuServlet.java

package servlet;

import
import java.sql.SQLException;

import javax.servlet.ServletException;

import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import dao.StudentDao;
import users.Student;

/**
* Servlet implementation class RegServlet
*/

public class DengLuServlet extends HttpServlet {
    private static final long serialVersionUID = 1L;

    /**
     * @see HttpServlet#HttpServlet()
     */
    public DengLuServlet() {
        super();
        // TODO Auto-generated constructor stub
    }

    /**
     * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
     */
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        // TODO Auto-generated method stub


    }

    /**
     * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)
     */
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        // TODO Auto-generated method stub
        request.setCharacterEncoding("utf-8");

        String username=request.getParameter("sname");
        String pwd=request.getParameter("spwd");

        Student st = new Student();
        StudentDao dao=new StudentDao();
        try {
            st=dao.getStudentOne(username,pwd);
        } catch (SQLException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
        if(st == null)
            response.sendRedirect("fail.jsp");
        else
            response.sendRedirect("exam.jsp");

    }

}

========================================================================

web.xml

<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns:xsi="http://www. xmlns="http://xmlns. xsi:schemaLocation="http://xmlns. http://xmlns. id="WebApp_ID" version="3.1">
  <display-name>denglu</display-name>

  <servlet>
      <servlet-name>DengluServlet</servlet-name>
      <servlet-class>DengluServlet</servlet-class>
  </servlet>
  <servlet-mapping>
      <servlet-name>DengluServlet</servlet-name>
      <url-pattern>/DengluServlet</url-pattern>
  </servlet-mapping>

  <servlet>
      <servlet-name>LoginServlet</servlet-name>
      <servlet-class>servlet.LoginServlet</servlet-class>
  </servlet>
  <servlet-mapping>
      <servlet-name>LoginServlet</servlet-name>
      <url-pattern>/LoginServlet</url-pattern>
  </servlet-mapping>
</web-app>