用户登录

用户登录案例需求：

1.编写login.html页面：usename&password两个输入框；

2.使用Druid数据库连接池技术，操作mysql,day14数据库中user表；

3.使用JDBCTemplate技术封装JDBC；

4.登陆成跳转到SusscessServlet展示：登陆成功！用户名，欢迎您。

5.登录失败跳转到FailServlet展示：登录失败，用户名或密码错误。

分析：

• loginServlet:

1.设置编码（解决中文乱码）

2.获取username和password

3.将username 和password封装为一个对象；

4.调用Username的login方法查询，获取返回值User对象；

5.判断user是否为null:*是：登录失败 *否：登录成功

• UserDao(操作数据库的类)

public User login(User user) { select*from user where user name=? and password =? }

开发步骤：

1.创建项目，导入配置文件和jar包；

2.创建数据库环境；

create database day14;
use day14;
create table user(
id int primary key auto_increment,
username varchar(32) unique not null,
password varchar(32) not null
);

3.创建包cn，创建user类-对应user表：

[注意]：Alt+Insert:生成getter setter方法 —— 再来一次toString

package cn;

//用户的实体类
public class User {
    
    private int id;
    private String username;
    private String password;


    public int getId() {
        return id;
    }

    public void setId(int id) {
        this.id = id;
    }

    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;
    }

    @Override
    public String toString() {
        return "User{" +
                "id=" + id +
                ", username='" + username + '\'' +
                ", password='" + password + '\'' +
                '}';
    }
}

4.创建cn.dao包，创建类UserDao（操作数据库中user表的类）,提供login方法；

package cn.dao;

import cn.User;
import org.springframework.dao.DataAccessException;
import org.springframework.jdbc.core.BeanPropertyRowMapper;
import org.springframework.jdbc.core.JdbcTemplate;
import util.JDBCUtil;


//操作数据库中User表的类
public class UserDao {
    /*
    登录方法：
    1.登录时只有用户名和密码；
    2.返回是信息全部；
     */
//使用成员template共用

    private JdbcTemplate template=new JdbcTemplate(JDBCUtil.getDataSource());
    public User login(User loginUser){

        try {

           //1.编写sql
            String sql="select* from user where username = ? and password = ?";
           //2.调用query方法
            User user=template.queryForObject(sql,
                    new BeanPropertyRowMapper<User>(User.class),
                    loginUser.getUsername(),loginUser.getPassword());
            return user;
        } catch (DataAccessException e) {
            e.printStackTrace();//记录日志
            return null;
        }
    }
}


//测试一下是否成功
package test;

import cn.User;
import cn.dao.UserDao;
import jdk.jfr.StackTrace;
import org.junit.Test;

public class UserDaotest {

@Test（Alt+Enter）
    public void test(){
    User loginuser=new User();
    loginuser.setUsername("baby");
    loginuser.setPassword("123");

    UserDao dao=new UserDao();
    User user=dao.login(loginuser);

    System.out.println(user);


    }

}

6.编写login.Servlet类：

import cn.User;
import cn.dao.UserDao;

import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;

@WebServlet("/lgoinServlet")
public class lgoinServlet extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
this.doGet(request,response);
    }

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
       // this.doPost(request, response);

        //1.设置编码
        request.setCharacterEncoding("utf-8");

        //2.获取请求参数
        String username= request.getParameter("username");
        String password=request.getParameter("password");
        
        //3.封装user对象
        User loginUser=new User();
        loginUser.setUsername(username);
        loginUser.setPassword(password);

        //4.调用User的login方法
        UserDao dao=new UserDao();
        User user=dao.login(loginUser);

        //5.判断user
        if(user==null)
            //登录失败
            request.getRequestDispatcher("failServlet").forward(request,response);
        else
            //登录成功
        //存储数据
            request.setAttribute("user",user);
        //转发
        request.getRequestDispatcher("/successServlet").forward(request,response);


    }
}

//FailServlet:

import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;

@WebServlet("/failServlet")
public class failServlet extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
//给页面写一句话
        //设置编码
        response.setContentType("text/html;charset=utf-8");

        //输出
        response.getWriter().write("登录失败，用户名或密码错误");


    }

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


//successServlet:

import cn.User;

import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;

@WebServlet("/successServlet")
public class sucessServlet extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        User user = (User) request.getAttribute("user");
        if (user != null) {

            //设置编码
            response.setContentType("text/html;charset=utf-8");

            //输出
            response.getWriter().write("登录成功！" + user.getUsername() + "欢迎您");
        }
    }
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        this.doPost(request, response);
    }
}

优化部分：

BeanUtils工具类：

作用：简化数据封装

修改部分:

    //2.获取所有请求参数
    Map<String,String[]> map=request.getParameterMap();
    //3.创建User对象
    User loginUser=new User();
    //3.2 使用BeanUtil封装
    try {
        BeanUtils.populate(loginUser,map);
    } catch (IllegalAccessException e) {
        e.printStackTrace();
    } catch (InvocationTargetException e) {
        e.printStackTrace();
    }