基于Servlet+JSP+JDBC的登录注册案例

这是一个适合学完Servlet+JSP+JDBC的练手例子，动手之前可以先回顾一下本文需要用到的知识 ~>
Servlet回顾：传送门
JSP回顾: 传送门

JDBC使用步骤回顾 ~>
1、加载驱动
2、获取连接对象
3、通过连接对象获取sql执行对象
4、编写sql语句
5、使用sql执行对象执行sql语句（为语句中的变量赋值）
6、sql执行对象调用执行方法
如果是查询调用executeQuery()；
如果是增删改调用executeUpdate()。
7、释放资源

Start ~>

1、创建一个javaweb工程，导入依赖

导入mysql连接：

<dependency>
	<groupId>mysql</groupId>
	<artifactId>mysql-connector-java</artifactId>
	<version>8.0.27</version>
</dependency>

2、创建数据库user表

在数据库中创建名为test的数据库，执行以下sql创建user表：

CREATE TABLE `user` (
`id` int(11) NOT NULL AUTO_INCREMENT,
`username` varchar(255) CHARACTER SET utf8 COLLATE utf8_general_ci DEFAULT NULL,
`password` varchar(255) DEFAULT NULL,
PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=10 DEFAULT CHARSET=utf8;

3、创建实体类

public class User {

    private Integer id;
    private String username;
    private String password;

    public User() {
    }

    public User(Integer id, String username, String password) {
        this.id = id;
        this.username = username;
        this.password = password;
    }

    public Integer getId() {
        return id;
    }

    public void setId(Integer 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;
    }
}

3、创建jdbc工具类

将JDBC中的一些步骤编写成工具类，减少重复代码。

public class JDBCUtil {

    static Connection connection = null;
    static PreparedStatement preparedStatement = null;
    static ResultSet resultSet = null;
	//加载驱动
    static {
        try {
            Class.forName("com.mysql.cj.jdbc.Driver");
        } catch (ClassNotFoundException e) {
            e.printStackTrace();
        }
    }
	//获取数据库连接
    public static Connection getConnection(){
        //数据库连接路径
        String url = "jdbc:mysql://localhost:3306/test?useUnicode=true&characterEncoding=utf-8";
        //数据库账号
        String username = "root";
        //数据库密码
        String password = "root";
        try {
            connection = DriverManager.getConnection(url,username,password);
        } catch (SQLException throwables) {
            throwables.printStackTrace();
        }
        return connection;
    }
	//释放资源
    public static void release(Connection connection,PreparedStatement preparedStatement){
        if (connection != null){
            try {
                connection.close();
            } catch (SQLException throwables) {
                throwables.printStackTrace();
            }
        }
        if (preparedStatement != null){
            try {
                preparedStatement.close();
            } catch (SQLException throwables) {
                throwables.printStackTrace();
            }
        }
    }
    public static void release(Connection connection,PreparedStatement preparedStatement,ResultSet resultSet){
        release(connection,preparedStatement);
        if (resultSet != null){
            try {
                resultSet.close();
            } catch (SQLException throwables) {
                throwables.printStackTrace();
            }
        }
    }

    public static void main(String[] args) {
        Connection connection = JDBCUtil.getConnection();
        System.out.println(connection);
    }

}

4、创建repository，编写登录方法（查询），注册方法（添加）

public class UserRepository {

    public void register(String username,String password){
        Connection connection = JDBCUtil.getConnection();
        PreparedStatement preparedStatement = null;
        String sql = "insert into user(username,password) values(?,?)";
        try {
            preparedStatement = connection.prepareStatement(sql);
            preparedStatement.setString(1,username);
            preparedStatement.setString(2,password);
            preparedStatement.executeUpdate();
        } catch (SQLException throwables) {
            throwables.printStackTrace();
        } finally {
            JDBCUtil.release(connection,preparedStatement);
        }
    }

    public User login(String username,String password){
        Connection connection = null;
        PreparedStatement preparedStatement = null;
        ResultSet resultSet = null;
        User user = null;
        String sql = "select * from user where username = ? and password = ?";
        try {
            connection = JDBCUtil.getConnection();
            preparedStatement = connection.prepareStatement(sql);
            preparedStatement.setString(1,username);
            preparedStatement.setString(2,password);
            resultSet = preparedStatement.executeQuery();
            while (resultSet.next()){
                int id = resultSet.getInt(1);
                String name = resultSet.getString(2);
                String pwd = resultSet.getString(3);
                user = new User(id,name,pwd);
            }
        } catch (SQLException throwables) {
            throwables.printStackTrace();
        } finally {
            JDBCUtil.release(connection,preparedStatement,resultSet);
        }
        return user;
    }

}

5、创建LoginServlet和RegisterServlet分别调用登录和注册方法

访问Servlet程序的映射可以在web.xml中配置，也可以使用注解@WebServlet替代，更为方便。

@WebServlet("/login")
public class LoginServlet extends HttpServlet {

    //访问：http://localhost:8080/login进入get方法，跳转到登录页面
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        resp.sendRedirect("index.jsp");
    }

    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        String username = req.getParameter("username");
        String password = req.getParameter("password");
        UserRepository userRepository = new UserRepository();
        User user = userRepository.login(username, password);
        if (user != null){
            req.getRequestDispatcher("homePage.jsp").forward(req,resp);
        }
        req.setAttribute("msg","用户名或密码错误！");
        req.getRequestDispatcher("index.jsp").forward(req,resp);
    }

}

@WebServlet("/register")
public class RegisterServlet extends HttpServlet {

    //访问：http://localhost:8080/register进入get方法，跳转到注册页面
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        req.getRequestDispatcher("register.jsp").forward(req,resp);
    }

    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        String username = req.getParameter("username");
        String password = req.getParameter("password");
        UserRepository userRepository = new UserRepository();
        userRepository.register(username,password);
        req.getRequestDispatcher("index.jsp").forward(req,resp);
    }

}

6、编写登录和注册页面 登录页面

登录页面

<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
    <title>登录</title>
</head>
<body>
<h1>LOGIN</h1>
<form action="/login" method="post">
    <div>
        <input type="text" name="username" placeholder="UserName">
    </div>
    <div>
        <input type="password" name="password" placeholder="UserPassword">
    </div>
    <input type="submit" value="Sign in">
    <a href="/register">Register</a>
</form>
<%
    String msg = (String)request.getAttribute("msg");
%>
<%
    if (msg != null){
        response.getWriter().write(msg);
    }
%>

</body>
</html>

注册页面

<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
    <title>注册</title>
</head>
<body>

<h1>register</h1>
<form action="/register" method="post">
    <div>
        <input type="text" name="username" placeholder="Enter UserName">
    </div>
    <div>
        <input type="password" name="password" placeholder="Enter UserPassword">
    </div>
    <input type="submit" value="Register">
</form>

</body>
</html>

主页

<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
    <title>主页</title>
</head>
<body>
<h1>Welcome!!!</h1>
</body>
</html>

运行截图：

7、添加过滤器

在注册的时候如果输入中文，在数据库中可以看到是乱码的，这时候可以使用过滤器来解决编码问题。
创建一个类实现Filter接口，在doFilter方法中设置编码为UTF-8：
注解@WebFilter("/*")表示过滤所有请求，如果你只想过滤部分请求，那么在斜杆之后加上请求的url即可，例如过滤注册请求：@WebFilter("/register")。

@WebFilter("/*")
public class MyFilter implements Filter {
    @Override
    public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {
        servletRequest.setCharacterEncoding("UTF-8");
        filterChain.doFilter(servletRequest,servletResponse);
    }
}

项目结构：