servlet和jsp编写登录注册页面完整教程

下面是一个简单的Servlet和JSP编写登录注册页面的完整教程。

1. 创建数据库表格

首先，我们需要创建一个名为“users”的数据库表格，包含以下字段：

- id（int，自增长）
- username（varchar）
- password（varchar）

2. 创建JavaBean类

然后，我们需要创建一个JavaBean类来代表用户：

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;
    }
}

3. 创建数据库访问类

接下来，我们需要创建一个类来处理与数据库的交互。我们将使用JDBC连接到MySQL数据库。在这个例子中，我们将使用一个简单的DAO模式（数据访问对象）来处理所有数据库访问：

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

public class UserDao {
    private String jdbcUrl;
    private String jdbcUsername;
    private String jdbcPassword;
    private Connection jdbcConnection;

    public UserDao(String jdbcUrl, String jdbcUsername, String jdbcPassword) {
        this.jdbcUrl = jdbcUrl;
        this.jdbcUsername = jdbcUsername;
        this.jdbcPassword = jdbcPassword;
    }

    protected void connect() throws SQLException {
        if (jdbcConnection == null || jdbcConnection.isClosed()) {
            try {
                Class.forName("com.mysql.jdbc.Driver");
            } catch (ClassNotFoundException e) {
                throw new SQLException(e);
            }
            jdbcConnection = DriverManager.getConnection(jdbcUrl, jdbcUsername, jdbcPassword);
        }
    }

    protected void disconnect() throws SQLException {
        if (jdbcConnection != null && !jdbcConnection.isClosed()) {
            jdbcConnection.close();
        }
    }

    public boolean addUser(User user) throws SQLException {
        String sql = "INSERT INTO users (username, password) VALUES (?, ?)";
        connect();

        PreparedStatement statement = jdbcConnection.prepareStatement(sql);
        statement.setString(1, user.getUsername());
        statement.setString(2, user.getPassword());

        boolean rowInserted = statement.executeUpdate() > 0;
        statement.close();
        disconnect();
        return rowInserted;
    }

    public User getUser(String username, String password) throws SQLException {
        String sql = "SELECT * FROM users WHERE username = ? AND password = ?";
        connect();

        PreparedStatement statement = jdbcConnection.prepareStatement(sql);
        statement.setString(1, username);
        statement.setString(2, password);

        ResultSet resultSet = statement.executeQuery();

        User user = null;

        if (resultSet.next()) {
            user = new User();
            user.setId(resultSet.getInt("id"));
            user.setUsername(resultSet.getString("username"));
            user.setPassword(resultSet.getString("password"));
        }

        resultSet.close();
        statement.close();

        disconnect();

        return user;
    }
}

4. 创建Servlet

现在我们可以创建一个Servlet来处理登录和注册请求。这个Servlet将使用我们刚刚创建的UserDao类来访问数据库。

import java.io.IOException;
import java.sql.SQLException;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

@WebServlet("/login")
public class LoginServlet extends HttpServlet {
    private static final long serialVersionUID = 1L;
    private UserDao userDao;

    public void init() {
        String jdbcUrl = "jdbc:mysql://localhost:3306/test";
        String jdbcUsername = "root";
        String jdbcPassword = "password";
        userDao = new UserDao(jdbcUrl, jdbcUsername, jdbcPassword);
    }

    protected void doPost(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {

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

        try {
            User user = userDao.getUser(username, password);
            if (user != null) {
                request.setAttribute("user", user);
                request.getRequestDispatcher("welcome.jsp").forward(request, response);
            } else {
                response.sendRedirect("login.jsp");
            }
        } catch (SQLException ex) {
            throw new ServletException(ex);
        }
    }
}

5. 创建JSP

最后，我们需要创建一个JSP文件来显示登录表单和欢迎消息。

<!DOCTYPE html>
<html>
<head>
    <title>Login</title>
</head>
<body>
    <h1>Login</h1>
    <form action="login" method="post">
        <label>Username:</label>
        <input type="text" name="username"><br><br>
        <label>Password:</label>
        <input type="password" name="password"><br><br>
        <input type="submit" value="Login">
    </form>
</body>
</html>

<!DOCTYPE html>
<html>
<head>
    <title>Welcome</title>
</head>
<body>
    <h1>Welcome <%= request.getAttribute("user").getUsername() %>!</h1>
</body>
</html>

6. 部署应用程序

现在，我们已经完成了我们的应用程序。我们只需要将它部署到一个Web服务器上，例如Tomcat或Jetty，就可以开始使用它了。

注意：这只是一个简单的例子，实际的Web应用程序需要更多的安全性和错误处理。