java web实现页面登陆

好像是这里面读不到数据，改了很久还是改不出来，求助！
package com.ding.dao;

import com.ding.entity.user;
import com.ding.util.DBHelper;
import java.sql.ResultSet;
import java.util.ArrayList;
import java.util.List;

/**
*

• @author irin
  */
  public class userDao extends DBHelper{

  public user login(String username, String password){
  user u = null;
  String sql = "select * from user where username = ? and password=?";
  
  try{
  ResultSet rs = this.executeQuery(sql,username,password);
  if(rs.next()){
  u = new user();
  u.setUsername(rs.getString(1));
  u.setPassword(rs.getString(2));
  
  }
  }catch(Exception e){
  e.printStackTrace();
  }finally{
  this.close();

  }   
  

  return u;
  
  }
  }

package com.ding.servlet;

import com.ding.dao.userDao;
import com.ding.entity.user;
import java.io.IOException;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

/**
*

• @author irin
  */
  public class userServlet extends HttpServlet {

  @Override
  protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
  doGet(req,resp);
  }
  private userDao userdao = new userDao();
  @Override
  protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
  req.setCharacterEncoding("utf-8");
  
  String username = req.getParameter("user");
  String password = req.getParameter("password");

  user u = new user();
  u.setUsername(username);
  u.setPassword(password);
  
  userDao userdao = new userDao();
  if(userdao.login(username,password)!=null){
      req.setAttribute("user",u );
      resp.sendRedirect("welcome.jsp");
  }
  else
      req.getRequestDispatcher("sorry.jsp").forward(req, resp);
  

  }

}

package com.ding.entity;

/**
*

• @author irin
  */
  public class user {
  // private int id;
  private String username;
  private String password;
  // private String role;

  public user() {
  }

  public user(String username, String password) {
  this.username = username;
  this.password = password;
  }

  public String getUsername() {
  return username;
  }

  public void setUsername(String username) {
  this.username = username;
  }

  public String getPassword() {
  return password;
  }

  public void setPassword(String password) {
  this.password = password;
  }

}

package com.ding.util;

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.util.logging.Level;
import java.util.logging.Logger;

/**
*

• @author irin
  */
  public class DBHelper {
  private Connection conn;
  private PreparedStatement ps;
  private ResultSet rs;

  //获得连接
  private void getConnection(){
  try {
  Class.forName("com.mysql.jdbc.Driver");
  String url = "jdbc:mysql://localhost:3306/dormitorymanage?characterEncoding=utf8&useSSL=true";
  conn = DriverManager.getConnection(url,"root","Ding1234");
  } catch (Exception e) {
  e.printStackTrace();
  }

  }

  //关闭
  public void close(){
  if(conn!=null){
  try {
  conn.close();
  } catch (Exception e) {
  e.printStackTrace();
  }
  conn = null;
  }

  if(ps!=null){
  try {
      ps.close();
  } catch (Exception e) {
      e.printStackTrace();
  }
      ps = null;
  }
  
  if(rs!=null){
  try {
      rs.close();
  } catch (Exception e) {
      e.printStackTrace();
  }
      rs = null;
  }
  

  }

  //更新--增加、修改、删除
  public int executeUpdate(String sql,Object...objects){
  try {
  this.getConnection();
  ps = conn.prepareStatement(sql);
  if(objects!=null){
  for(int i=0;i<objects.length;i++){
  ps.setObject(i+1, objects[i]);
  }
  }
  return ps.executeUpdate();
  } catch (SQLException e) {
  e.printStackTrace();
  }finally{
  this.close();
  }
  return -1;
  
  }

  //查询
  public ResultSet executeQuery(String sql,Object...objects){
  try {
  this.getConnection();
  ps = conn.prepareStatement(sql);
  if(objects!=null){
  for(int i=0;i<objects.length;i++){
  ps.setObject(i+1, objects[i]);
  }
  }
  return rs = ps.executeQuery();
  } catch (SQLException e) {
  e.printStackTrace();
  }
  return null;
  
  }
  }