JavaWeb，不使用框架下的MVC模式简单登陆模块实现

项目结构图

1. 前期准备

本项目使用的jdk版本是：jdk1.8.0_181
本项目使用的tomcat版本是：apache-tomcat-7.0.90
本项目使用的mysql数据库版本是：mysql8.0
本项目使用的数据库驱动是：mysql-connector-java-8.0.12.jar
本项目使用的编辑器是：IntelliJ IDEA 2017.1
如果环境不一致，请修改相应的代码，数据库部分请按照自己的用户名密码数据库的名称进行相应的修改，数据库连接部分请在文件JDBCUtil中进行相应的修改，数据表名称的修改请在UserDaoImpl中进行修改。

2. 项目代码

后台源代码
com.cx.bean.User.java

package com.cx.bean;

/**
 * Created by admin on 2018/8/14.
 */
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;
    }
}

com.cx.dao.user.UsrDao.java

package com.cx.dao.user;

import com.cx.bean.User;

/**
 * Created by admin on 2018/8/14.
 */
public interface UserDao {
    User queryByUsername(String username);//返回查询到的用户

}

com.cx.dao.user.impl.UserDaoImpl.java

package com.cx.dao.user.impl;

import com.cx.bean.User;
import com.cx.dao.user.UserDao;
import com.cx.utils.JDBCUtil;

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

/**
 * Created by admin on 2018/8/14.
 */
public class UserDaoImpl implements UserDao{
    User user = null;
    Connection connection = null;
    PreparedStatement preparedStatement = null;
    ResultSet resultSet = null;
    @Override
    public User queryByUsername(String username) {
        //根据用户名查询用户，并返回用户

        try {
            connection = JDBCUtil.getConnect();//首先连接数据库
            String sql = "select * from user_table where name=?";//写出sql语句
            preparedStatement = connection.prepareStatement(sql);//执行sql语句
            preparedStatement.setString(1,username);//为sql语句中的变量赋值
            resultSet = preparedStatement.executeQuery();//获得查询结果集
            if (resultSet.next()){
                user = new User();
                user.setId(Integer.parseInt(resultSet.getString("ID")));//将数据库中取出来的id字段字符类型转换为整型并赋给user对象
                user.setPassword(resultSet.getString("password"));
                user.setUsername(resultSet.getString("name"));
            }

        } catch (SQLException e) {
            e.printStackTrace();
        }finally {
            JDBCUtil.close(preparedStatement,connection,resultSet);
        }



        return user;
    }
}

com.cx.service.user.UserService.java

package com.cx.service.user;

import com.cx.bean.User;

/**
 * Created by admin on 2018/8/14.
 */
public interface UserService {
    User queryByUsername(String username);
}

com.cx.service.impl.UserServiceImpl.java

package com.cx.service.user.impl;

import com.cx.bean.User;
import com.cx.dao.user.impl.UserDaoImpl;
import com.cx.service.user.UserService;

/**
 * Created by admin on 2018/8/14.
 */
public class UserServiceImpl implements UserService {

    UserDaoImpl userDaoImpl = null;
    @Override
    public User queryByUsername(String username) {
        User user = new User();
        userDaoImpl = new UserDaoImpl();
        user = userDaoImpl.queryByUsername(username);
        return user;
    }
}

com.cx.controller.LoginController.java

package com.cx.controller;

import com.cx.bean.User;
import com.cx.dao.user.impl.UserDaoImpl;
import com.cx.utils.MD5Util;

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;

/**
 * Created by admin on 2018/8/14.
 */
@WebServlet("/login.do")
public class LoginController extends HttpServlet {
    public LoginController(){
        super();
    }

    private UserDaoImpl userDaoImpl = null;

    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        doPost(req, resp);

    }

    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {

        //调用login方法
        User user = login(req);
        if (user != null){
            req.setAttribute("user",user);
            req.getRequestDispatcher("/success.jsp").forward(req,resp);
        }else {
            req.getRequestDispatcher("/error.jsp").forward(req,resp);
        }
    }

    public User login(HttpServletRequest request) {

        String username = request.getParameter("username");
        String password = request.getParameter("password");

        userDaoImpl = new UserDaoImpl();
        User user = userDaoImpl.queryByUsername(username);
        if (MD5Util.string2MD5(password).equals(user.getPassword())){
            return user;
        }else {
            return null;
        }



    }
}

com.cx.utils.JDBCUtil.java

package com.cx.utils;

import java.sql.*;

/**
 * Created by admin on 2018/8/14.
 */
public class JDBCUtil {
    //定义出来数据库连接的信息
    private static String url = "jdbc:mysql://192.168.99.206:3306/homework?serverTimezone=UTC&useSSL=false";//数据库连接地址
    private static String user = "root";//数据库连接用户名
    private static String password = "123456";//数据库连接密码
    private static String driver = "com.mysql.cj.jdbc.Driver";//数据库连接驱动

    static {
        //获取驱动类
        try {
            Class.forName(driver);
        } catch (ClassNotFoundException e) {
            e.printStackTrace();
        }
    }

    //数据库连接
    public static Connection getConnect() throws SQLException {
        Connection conn = null;
        conn = (Connection) DriverManager.getConnection(url,user,password);
        return conn;
    }

    //数据库关闭
    public static void close(PreparedStatement preparedStatement, Connection connection, ResultSet resultSet){

        if (preparedStatement != null){
            try {
                preparedStatement.close();
            } catch (SQLException e) {
                e.printStackTrace();
            }
        }

        if (connection != null){
            try {
                connection.close();
            } catch (SQLException e) {
                e.printStackTrace();
            }
        }

        if (resultSet != null){
            try {
                resultSet.close();
            } catch (SQLException e) {
                e.printStackTrace();
            }
        }
    }

}

com.cx.utils.MD5Util.java

package com.cx.utils;

import java.security.MessageDigest;

/**
 * Created by admin on 2018/8/14.
 */
public class MD5Util {

    /***
     * MD5加码 生成32位md5码
     */
    public static String string2MD5(String inStr){
        MessageDigest md5 = null;
        try{
            md5 = MessageDigest.getInstance("MD5");
        }catch (Exception e){
            System.out.println(e.toString());
            e.printStackTrace();
            return "";
        }
        char[] charArray = inStr.toCharArray();
        byte[] byteArray = new byte[charArray.length];

        for (int i = 0; i < charArray.length; i++)
            byteArray[i] = (byte) charArray[i];
        byte[] md5Bytes = md5.digest(byteArray);
        StringBuffer hexValue = new StringBuffer();
        for (int i = 0; i < md5Bytes.length; i++){
            int val = ((int) md5Bytes[i]) & 0xff;
            if (val < 16)
                hexValue.append("0");
            hexValue.append(Integer.toHexString(val));
        }
        return hexValue.toString();

    }

    /**
     * 加密解密算法 执行一次加密，两次解密
     */
    public static String convertMD5(String inStr){

        char[] a = inStr.toCharArray();
        for (int i = 0; i < a.length; i++){
            a[i] = (char) (a[i] ^ 't');
        }
        String s = new String(a);
        return s;

    }

    // 测试主函数
    public static void main(String args[]) {
        String s = new String("123456");
        System.out.println("原始：" + s);
        System.out.println("MD5后：" + string2MD5(s));
        System.out.println("加密的：" + convertMD5(s));
        System.out.println("解密的：" + convertMD5(convertMD5(s)));

    }
}

前端JSP
index.jsp

<%--
  Created by IntelliJ IDEA.
  User: admin
  Date: 2018/8/14
  Time: 9:18
  To change this template use File | Settings | File Templates.
--%>
<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
  <head>
    <title>首页</title>
  </head>
  <body>
  <H1>这是首页</H1>
  <h1>请<a href="../login.jsp">登陆</a> </h1>
  </body>
</html>

login.jsp

<%--
  Created by IntelliJ IDEA.
  User: admin
  Date: 2018/8/14
  Time: 11:06
  To change this template use File | Settings | File Templates.
--%>
<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
    <title>登陆界面</title>
</head>
<body>
<form action="../login.do" method="post">
    <table>
        <tr>
            <td>用户名：</td>
            <td><input name="username" type="text" value=""/></td>
        </tr>
        <tr>
            <td>密  码：</td>
            <td><input name="password" type="password" value=""/></td>
        </tr>
        <tr>
            <td><input type="reset" value="重置"></td>
            <td><input type="submit" value="提交"/></td>
        </tr>
    </table>
</form>
</body>
</html>

success.jsp

<%@ page import="com.cx.bean.User" %>
<%--
  Created by IntelliJ IDEA.
  User: admin
  Date: 2018/8/14
  Time: 10:58
  To change this template use File | Settings | File Templates.
--%>
<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
    <title>登陆成功页面</title>
</head>
<body>
<%
    User user = (User) request.getAttribute("user");

%>
<h1>登陆成功！</h1>
<h1>用户ID：<%=user.getId() %></h1>
<h1>用户名：<%=user.getUsername() %></h1>
</body>
</html>

error.jsp

<%--
  Created by IntelliJ IDEA.
  User: admin
  Date: 2018/8/14
  Time: 11:04
  To change this template use File | Settings | File Templates.
--%>
<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
    <title>登陆失败页面</title>
</head>
<body>
<h1>登陆失败！请重新<a href="../login.jsp">登陆</a> </h1>
</body>
</html>

3. 运行结果

4. 其他注意事项

本项目中的数据库名为homgwork，数据表名为user_table，其中的字段有ID、name、password等。
本项目中用于验证的密码都是通过MD5Util类进行了md5加密，请首先通过该类将加密后的password写入到对应的数据表中的password字段，否则就会登录不成功，也可以在登陆验证的地方去掉md5加密验证。
本项目中的运行时可能会出现缺少servlet-api.jar的错误提示，这时候只需要将tomcat目录下的lib目录中的jsp-api.jar和servlet-api.jar两个jar包导入项目中即可。