java实现用户注册和登录

用户注册和登录是 Web 应用程序的基本功能之一。下面是一个简单的 Java Web 应用程序示例，演示如何实现用户注册和登录功能。

1. 创建一个 User 类，其中包含用户的基本信息，如用户名、密码和电子邮件地址。

public class User {
    private String username;
    private String password;
    private String email;

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

    public String getUsername() {
        return username;
    }

    public String getPassword() {
        return password;
    }

    public String getEmail() {
        return email;
    }
}

2. 创建一个 UserDao 类，该类负责将用户信息存储在数据库中，并且提供方法来验证用户的登录信息和创建新用户的信息。

public class UserDao {
    private Connection conn;

    public UserDao() {
        try {
            Class.forName("com.mysql.jdbc.Driver");
            conn = DriverManager.getConnection("jdbc:mysql://localhost:3306/mydb", "root", "password");
        } catch (ClassNotFoundException | SQLException e) {
            e.printStackTrace();
        }
    }

    public boolean register(User user) {
        try {
            PreparedStatement stmt = conn.prepareStatement("INSERT INTO users (username, password, email) VALUES (?, ?, ?)");
            stmt.setString(1, user.getUsername());
            stmt.setString(2, user.getPassword());
            stmt.setString(3, user.getEmail());
            stmt.executeUpdate();
            return true;
        } catch (SQLException e) {
            e.printStackTrace();
            return false;
        }
    }

    public boolean login(String username, String password) {
        try {
            PreparedStatement stmt = conn.prepareStatement("SELECT * FROM users WHERE username=? AND password=?");
            stmt.setString(1, username);
            stmt.setString(2, password);
            ResultSet rs = stmt.executeQuery();
            if (rs.next()) {
                return true;
            } else {
                return false;
            }
        } catch (SQLException e) {
            e.printStackTrace();
            return false;
        }
    }
}

3. 创建一个 RegisterServlet 类，该类负责处理用户注册请求。

@WebServlet("/register")
public class RegisterServlet extends HttpServlet {
    private UserDao userDao;

    public void init() {
        userDao = new UserDao();
    }

    public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        request.getRequestDispatcher("register.jsp").forward(request, response);
    }

    public void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        String username = request.getParameter("username");
        String password = request.getParameter("password");
        String email = request.getParameter("email");
        User user = new User(username, password, email);
        if (userDao.register(user)) {
            response.sendRedirect("login.jsp");
        } else {
            request.setAttribute("message", "Registration failed");
            request.getRequestDispatcher("register.jsp").forward(request, response);
        }
    }
}

4. 创建一个 LoginServlet 类，该类负责处理用户登录请求。

@WebServlet("/login")
public class LoginServlet extends HttpServlet {
    private UserDao userDao;

    public void init() {
        userDao = new UserDao();
    }

    public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        request.getRequestDispatcher("login.jsp").forward(request, response);
    }

    public void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        String username = request.getParameter("username");
        String password = request.getParameter("password");
        if (userDao.login(username, password)) {
            HttpSession session = request.getSession();
            session.setAttribute("username", username);
            response.sendRedirect("home.jsp");
        } else {
            request.setAttribute("message", "Invalid username or password");
            request.getRequestDispatcher("login.jsp").forward(request, response);
        }
    }
}

5. 创建一个 register.jsp 页面，该页面包含一个表单，用户可以在其中输入他们的注册信息。

<html>
<head>
    <meta charset="UTF-8">
    <title>Register</title>
</head>
<body>
    <h1>Register</h1>
    <form action="register" method="post">
        <label for="username">Username:</label>
        <input type="text" name="username" id="username"><br>
        <label for="password">Password:</label>
        <input type="password" name="password" id="password"><br>
        <label for="email">Email:</label>
        <input type="email" name="email" id="email"><br>
        <input type="submit" value="Register">
    </form>
    <p>${message}</p>
</body>
</html>

6. 创建一个 login.jsp 页面，该页面包含一个表单，用户可以在其中输入他们的登录信息。

<html>
<head>
    <meta charset="UTF-8">
    <title>Login</title>
</head>
<body>
    <h1>Login</h1>
    <form action="login" method="post">
        <label for="username">Username:</label>
        <input type="text" name="username" id="username"><br>
        <label for="password">Password:</label>
        <input type="password" name="password" id="password"><br>
        <input type="submit" value="Login">
    </form>
    <p>${message}</p>
</body>
</html>

7. 创建一个 home.jsp 页面，该页面显示用户已登录。

<html>
<head>
    <meta charset="UTF-8">
    <title>Home</title>
</head>
<body>
    <h1>Welcome ${username}!</h1>
    <a href="logout">Logout</a>
</body>
</html>

这就是一个简单的 Java Web 应用程序示例，演示了如何实现用户注册和登录功能。