向大佬们低头，能帮我的代码每行都加些注释吗？实在小白!!还有能说说这俩段代码实现了登陆功能吗？

java

 package service;

import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;

import dao.SqlUtil;

import model.User;

public class LoginCheck {

    public User LoginCheck(User user) {
        Connection con = SqlUtil.getConnection();
        User resuser = new User();
        try {
            PreparedStatement ps = con
                    .prepareStatement("select * from student where loginname = '"
                            + user.getLoginname()
                            + "'and password = '"
                            + user.getPassword() + "'");

            ResultSet result = (ResultSet) ps.executeQuery();

            if (result.next()) {

                resuser.setUsername(result.getString("name"));
                resuser.setDeptid(result.getString("deptid"));
                resuser.setId(result.getString("id"));
                resuser.setLoginname(result.getString("loginname"));
                resuser.setPassword(result.getString("password"));
                resuser.setRoleid(result.getString("roleid"));
            } else {
            }

        } catch (SQLException e) {
            e.printStackTrace();
        }
        return resuser;
    }

}

servlet

 package servlets;
import javax.servlet.*;
import java.io.*;
import javax.servlet.http.*;
import service.LoginCheck;
import model.User;


/*
 * 该类接受login界面的数据，并进行处理
 */
public class LoginServlet extends HttpServlet {
    public void doGet(HttpServletRequest request, HttpServletResponse response)
            throws IOException, ServletException {
        String userid = request.getParameter("userid");// 接受页面传送过来userid的值
        String userpass = request.getParameter("userpass");

        User user = new User();// 实例化 判断类（UserBean）
        user.setLoginname(userid);
        user.setPassword(userpass);

        LoginCheck loginCheck = new LoginCheck();

        User forword = loginCheck.LoginCheck(user);

        if (forword.getId() == null) {
            RequestDispatcher dispatcher = request
                    .getRequestDispatcher("login.jsp?error=password error");
            dispatcher.forward(request, response);
        } else {
            request.getSession().setAttribute("user",user);
            RequestDispatcher dispatcher = request
                    .getRequestDispatcher("contents.jsp");
            dispatcher.forward(request, response);// 跳转显示页面
        }
    }

    public void doPost(HttpServletRequest request, HttpServletResponse response)
            throws IOException, ServletException {
        doGet(request, response);
    }
}

接受数据，判断数据库里面是否有这个记录，有就登陆成功转到content.jsp，没有就登陆失败返回login,jsp

这就是个登录的逻辑啊