servlet+jdbc+jsp实现登录界面的验证（基于MVC思想）

一、MVC的概念

MVC是模型(Model)和视图(View)以及控制器(Controller)的简写，是一种将数据、界面显示和业务逻辑进行分离的组织方式，这样在改进界面及用户交互时，不需要重新编写业务逻辑，从而提高了代码的可维护性。

M：主要用于封装业务数据的JavaBean(Bean) 和业务逻辑的JavaBean(Service)及访问数据库的

DAO对象。

V：主要负责数据收集和数据展现，通常由JSP文件完成。
C：主要负责流程控制和页面跳转，通常由Servlet完成。

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原始的登录验证方法：

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改进的登录验证方法：

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这样实现了解耦，从而具备了更好的扩展性。

二、需求

浏览器进入登录界面，输入用户名、密码，发送到服务器。
服务器完成数据库查询和验证，返回验证结果。
验证结果呈现在响应界面上。

三、代码演示

1、编写登录界面

创建空工程，在工程中创建javaEE模块
配置中设置tomcat的部署

编写login界面

<%@ page contentType="text/html; charset=UTF-8" pageEncoding="UTF-8" %>
<!DOCTYPE html>
<html>
<head><title>JSP - login</title>
</head>
<body>
<form action="loginServlet" method="post">用户名：<input type="text" name="userName"><br>密  码：<input type="text" name="password"><br><input type="submit" value="登录">
</form>
</body>

```

2、编写LoginServlet实现获取用户名和密码

编写servlet

LoginServlet

package com.example.login_demo.servlet;import com.example.login_demo.pojo.User;
import com.example.login_demo.service.UserService;import javax.servlet.*;
import javax.servlet.http.*;
import javax.servlet.annotation.*;
import java.io.IOException;@WebServlet(name = "LoginServlet", value = "/loginServlet")
public class LoginServlet extends HttpServlet {@Overrideprotected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {this.doPost(request, response);}@Overrideprotected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {//1、获取的用户名和密码String userName = request.getParameter("userName");System.out.println("获取的用户名：" + userName);String password = request.getParameter("password");System.out.println("获取的密码：" + password);}
}

单元测试：
- 运行tomcat
- 访问登录界面，发送登录请求

3、操作数据库部分

数据准备，db_web数据库下准备t_user表

编写DbUtils，实现jdbc的封装

package com.example.login_demo.utils;import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.SQLException;public class DbUtils {private static String jdbcName;private static String dbUrl;private static String dbUserName;private static String dbPassword;static {jdbcName = "com.mysql.jdbc.Driver";dbUrl = "jdbc:mysql://localhost:3306/db_web?useSSL=false";dbUserName = "root";dbPassword = "root";try {Class.forName(jdbcName);} catch (ClassNotFoundException e) {e.printStackTrace();}}public static Connection getConnection() throws SQLException {Connection connection = DriverManager.getConnection(dbUrl, dbUserName, dbPassword);return connection;}public static void closeResource(Connection connection, PreparedStatement preparedStatement) throws SQLException {if (null != connection){connection.close();}if (null != preparedStatement){preparedStatement.close();}}}

原始数据类型User

package com.example.login_demo.pojo;public class User {private int id;private String userName;private String password;public User(String userName, String password) {this.userName = userName;this.password = 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;}@Overridepublic String toString() {return "User{" +"id=" + id +", userName='" + userName + '\'' +", password='" + password + '\'' +'}';}
}

dao层直接操作数据库

UserDao接口

package com.example.login_demo.dao;import com.example.login_demo.pojo.User;public interface UserDao {//查询用户User userLogin(User user);
}

UserDaoImpl接口实现类

package com.example.login_demo.dao;import com.example.login_demo.pojo.User;
import com.example.login_demo.utils.DbUtils;import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;public class UserDaoImpl implements UserDao {@Overridepublic User userLogin(User user) {Connection connection = null;PreparedStatement preparedStatement = null;ResultSet resultSet = null;try {//1、获取数据库连接connection = DbUtils.getConnection();//2、准备sql语句String sql = "select * from t_user where userName = ? and password = ?";//3、执行sql返回结果preparedStatement = connection.prepareStatement(sql);preparedStatement.setString(1, user.getUserName());preparedStatement.setString(2, user.getPassword());resultSet = preparedStatement.executeQuery();if (resultSet.next()){User returnUser = new User(resultSet.getString("userName"), resultSet.getString("password"));returnUser.setId(Integer.parseInt(resultSet.getString("id")));return returnUser; //查找成功}}catch (SQLException e){e.printStackTrace();}finally {//4、释放资源try {DbUtils.closeResource(connection, preparedStatement);if (null != resultSet){resultSet.close();}} catch (SQLException e) {e.printStackTrace();}}return null;//查找失败}public static void main(String[] args) {UserDao userDao = new UserDaoImpl();User admin = userDao.userLogin(new User("admin", "12345"));System.out.println("查找到的用户：" + admin);}
}

单元测试：
- 执行UserDaoImpl中的测试代码

4、service层实现

UserDaoFactory实现：简单的静态工厂实现UserDao的实例创建，实现创建和使用的解耦

package com.example.login_demo.factory;import com.example.login_demo.dao.UserDao;
import com.example.login_demo.dao.UserDaoImpl;public class UserDaoFactory {public static UserDao getUserDao(){return new UserDaoImpl();}
}

service层实现dao层调用

package com.example.login_demo.service;import com.example.login_demo.dao.UserDao;
import com.example.login_demo.factory.UserDaoFactory;
import com.example.login_demo.pojo.User;public class UserService {private UserDao userDao;public UserService(){this.userDao = UserDaoFactory.getUserDao();}public User userLoginService(User user){return userDao.userLogin(user);}}

5、修改Servlet，实现数据库的查找验证

LoginServlet

package com.example.login_demo.servlet;import com.example.login_demo.pojo.User;
import com.example.login_demo.service.UserService;import javax.servlet.*;
import javax.servlet.http.*;
import javax.servlet.annotation.*;
import java.io.IOException;@WebServlet(name = "LoginServlet", value = "/loginServlet")
public class LoginServlet extends HttpServlet {@Overrideprotected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {this.doPost(request, response);}@Overrideprotected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {//1、获取的用户名和密码String userName = request.getParameter("userName");System.out.println("获取的用户名：" + userName);String password = request.getParameter("password");System.out.println("获取的密码：" + password);//2、创建UserService类型的对象实现数据的校验功能UserService userService = new UserService();User user = userService.userLoginService(new User(userName, password));if (null != user){System.out.println("登录成功！");}else {System.out.println("登录失败！");}}
}

单元测试：

6、修改Servlet，实现页面的跳转

修改LoginServlet，当成功时，跳转到成功界面；当失败时，跳转回登录界面并显示账号或者密码错误

package com.example.login_demo.servlet;import com.example.login_demo.pojo.User;
import com.example.login_demo.service.UserService;import javax.servlet.*;
import javax.servlet.http.*;
import javax.servlet.annotation.*;
import java.io.IOException;@WebServlet(name = "LoginServlet", value = "/loginServlet")
public class LoginServlet extends HttpServlet {@Overrideprotected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {this.doPost(request, response);}@Overrideprotected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {//1、获取的用户名和密码String userName = request.getParameter("userName");System.out.println("获取的用户名：" + userName);String password = request.getParameter("password");System.out.println("获取的密码：" + password);//2、创建UserService类型的对象实现数据的校验功能UserService userService = new UserService();User user = userService.userLoginService(new User(userName, password));if (null != user){System.out.println("登录成功！");//登录成功的信息放入session对象实现多个请求共享request.getSession().setAttribute("user", user);//实现客户端跳转response.sendRedirect("main.jsp");}else {System.out.println("登录失败，用户名或者密码错误！");request.setAttribute("error", "登录失败，用户名或者密码错误！");//实现服务器跳转，使用转发，共享requestRequestDispatcher requestDispatcher = request.getRequestDispatcher("login.jsp");requestDispatcher.forward(request, response);}}
}

main.jsp

<%@ page import="com.example.login_demo.pojo.User" %>
<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head><title>主页面</title>
</head>
<body>
<h1>登录成功！欢迎 <%=(User)session.getAttribute("user")%> !</h1>
</body>
</html>

<%@ page contentType="text/html; charset=UTF-8" pageEncoding="UTF-8" %>
<!DOCTYPE html>
<html>
<head><title>JSP - login</title>
</head>
<body>
<form action="loginServlet" method="post">用户名：<input type="text" name="userName"><br>密  码：<input type="text" name="password"><br><span style="color: red"><%=request.getAttribute("error") == null?"":request.getAttribute("error")%></span><br><input type="submit" value="登录">
</form>
</body>
</html>