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 ~>

操作步骤

1、创建一个javaweb工程，导入依赖
2、创建数据库user表
3、创建实体类
3、创建jdbc工具类
4、创建repository，编写登录方法（查询），注册方法（添加）
5、创建LoginServlet和RegisterServlet分别调用登录和注册方法
6、编写登录和注册页面登录页面
7、添加过滤器

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@Overrideprotected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {resp.sendRedirect("index.jsp");}@Overrideprotected 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@Overrideprotected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {req.getRequestDispatcher("register.jsp").forward(req,resp);}@Overrideprotected 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 {@Overridepublic void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {servletRequest.setCharacterEncoding("UTF-8");filterChain.doFilter(servletRequest,servletResponse);}
}

项目结构：