Java 登录注册功能代码实现

Java 实现登录注册功能的代码实现需要使用到数据库连接和操作，以下是一个简单的示例代码：

1. 首先，创建一个名为 `User` 的 Java 类，包含用户的基本信息，如用户名、密码等。

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

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

    public String getUsername() {
        return username;
    }

    public String getPassword() {
        return password;
    }
}

2. 创建一个名为 `Database` 的 Java 类，用于连接和操作数据库。这里使用 MySQL 数据库作为示例。

import java.sql.*;

public class Database {
    private Connection connection;
    private Statement statement;

    public Database(String url, String username, String password) throws SQLException {
        connection = DriverManager.getConnection(url, username, password);
        statement = connection.createStatement();
    }

    public ResultSet executeQuery(String query) throws SQLException {
        return statement.executeQuery(query);
    }

    public int executeUpdate(String query) throws SQLException {
        return statement.executeUpdate(query);
    }

    public void close() throws SQLException {
        if (statement != null) {
            statement.close();
        }

        if (connection != null) {
            connection.close();
        }
    }
}

3. 在 `Database` 类中添加以下方法，用于创建用户表和插入用户数据：

public void createUserTable() throws SQLException {
    String query = "CREATE TABLE IF NOT EXISTS users (" +
        "id INT(11) NOT NULL AUTO_INCREMENT," +
        "username VARCHAR(255) NOT NULL," +
        "password VARCHAR(255) NOT NULL," +
        "PRIMARY KEY (id)," +
        "UNIQUE KEY username (username)" +
        ");";

    statement.executeUpdate(query);
}

public void insertUser(User user) throws SQLException {
    String query = "INSERT INTO users (username, password) VALUES (" +
        "'" + user.getUsername() + "'," +
        "'" + user.getPassword() + "'" +
        ");";

    statement.executeUpdate(query);
}

4. 在主程序中，实例化 `Database` 类并创建用户表。然后，可以使用以下代码来注册新用户：

Database db = new Database("jdbc:mysql://localhost:3306/test", "root", "password");

db.createUserTable();

User user = new User("Alice", "mypassword");

db.insertUser(user);

5. 实现登录功能，可以使用以下代码：

public boolean login(String username, String password) throws SQLException {
    String query = "SELECT * FROM users WHERE username='" + username + "' AND password='" + password + "';";
    ResultSet result = statement.executeQuery(query);

    return result.next();
}

在以上示例中，我们使用 `login` 方法来检查给定的用户名和密码是否与数据库中的数据匹配。如果是，`ResultSet` 将包含一条记录，并返回 `true`；否则，将返回 `false`。

完整代码如下：

import java.sql.*;

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

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

    public String getUsername() {
        return username;
    }

    public String getPassword() {
        return password;
    }
}

public class Database {
    private Connection connection;
    private Statement statement;

    public Database(String url, String username, String password) throws SQLException {
        connection = DriverManager.getConnection(url, username, password);
        statement = connection.createStatement();
    }

    public ResultSet executeQuery(String query) throws SQLException {
        return statement.executeQuery(query);
    }

    public int executeUpdate(String query) throws SQLException {
        return statement.executeUpdate(query);
    }

    public void close() throws SQLException {
        if (statement != null) {
            statement.close();
        }

        if (connection != null) {
            connection.close();
        }
    }

    public void createUserTable() throws SQLException {
        String query = "CREATE TABLE IF NOT EXISTS users (" +
            "id INT(11) NOT NULL AUTO_INCREMENT," +
            "username VARCHAR(255) NOT NULL," +
            "password VARCHAR(255) NOT NULL," +
            "PRIMARY KEY (id)," +
            "UNIQUE KEY username (username)" +
            ");";

        statement.executeUpdate(query);
    }

    public void insertUser(User user) throws SQLException {
        String query = "INSERT INTO users (username, password) VALUES (" +
            "'" + user.getUsername() + "'," +
            "'" + user.getPassword() + "'" +
            ");";

        statement.executeUpdate(query);
    }

    public boolean login(String username, String password) throws SQLException {
        String query = "SELECT * FROM users WHERE username='" + username + "' AND password='" + password + "';";
        ResultSet result = statement.executeQuery(query);

        return result.next();
    }
}

public class Main {
    public static void main(String[] args) {
        try {
            Database db = new Database("jdbc:mysql://localhost:3306/test", "root", "password");

            db.createUserTable();

            User user = new User("Alice", "mypassword");

            db.insertUser(user);

            boolean success = db.login("Alice", "mypassword");

            System.out.println("Login success: " + success);

            db.close();
        } catch (SQLException e) {
            e.printStackTrace();
        }
    }
}