${requestScope["login.message"]}

  <form action="${pageContext.request.contextPath}/login" method="post">
  username:<input type="text" name="username"><br>
  password:<input type="password" name="password"><br>
  <input type="submit" value="提交">
  </form>

public void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        //获取表单提交的数据username和password
        String username = request.getParameter("username");
        String password = request.getParameter("password");
        //封装属性
        User user = new User();
        user.setUsername(username);
        user.setPassword(password);
        //调用UserService中的login方法
        UserService service = new UserService();
        User existUser = service.login(user);
        //查询结果
        if(existUser == null){
            request.setAttribute("login.message", "用户名密码错误");
            request.getRequestDispatcher("/login.jsp").forward(request, response);
            return;
        }else{
//验证成功跳转到success页面显示session数据的email
            request.getSession().setAttribute("user", existUser);
            response.sendRedirect(request.getContextPath()+"/success.jsp");
            return;
        }

    }

public User login(User user) {
        return new UserDao().findUser(user);
}

public User findUser(User user) {   
//sql语句
        String sql = "select * from user where username='"+user.getUsername()+"' and password='"+user.getPassword()+"'";    
//数据库连接，读取数据，循环遍历
        Connection con = null;
        Statement st = null;
        ResultSet rs = null;    
        try {
            con = JdbcUtils.getConnection();
            st = con.createStatement();
            rs = st.executeQuery(sql);
            if(rs.next()){
                User u = new User();
                u.setId(rs.getInt("id"));
                u.setUsername(rs.getString("username"));
                u.setUsername(rs.getString("password"));
                u.setUsername(rs.getString("email"));
                return u;
            }   
        } catch (SQLException e) {
            e.printStackTrace();
        }
        return null;
    }

driverClass=com.mysql.jdbc.Driver
url=jdbc:mysql:///test
username=root
password=123456

  success ${user.username}