用java和MySQL实现一个访客管理系统，这个系统有一个黑名单功能，这个黑名单功能可以进行增删改查功能，并且这个系统已经包含异常处理，请给出详细代码。并详细解释这些代码的意思。

以下是用Java和MySQL实现访客管理系统的代码，包含黑名单的增删改查功能和异常处理：

1. 首先创建一个Visitor类，包含访客的姓名、电话和是否在黑名单中的状态。

public class Visitor {
    private String name;
    private String phone;
    private boolean isBlacklisted;

    public Visitor(String name, String phone, boolean isBlacklisted) {
        this.name = name;
        this.phone = phone;
        this.isBlacklisted = isBlacklisted;
    }

    public String getName() {
        return name;
    }

    public String getPhone() {
        return phone;
    }

    public boolean isBlacklisted() {
        return isBlacklisted;
    }

    public void setBlacklisted(boolean blacklisted) {
        isBlacklisted = blacklisted;
    }
}

2. 创建一个VisitorDAO类，处理与访客数据库的交互。

import java.sql.*;

public class VisitorDAO {
    private final String url = "jdbc:mysql://localhost:3306/visitor_management_system";
    private final String user = "root";
    private final String password = "password";

    public VisitorDAO() {
        try {
            Class.forName("com.mysql.cj.jdbc.Driver");
        } catch (ClassNotFoundException e) {
            e.printStackTrace();
        }
    }

    public Connection getConnection() throws SQLException {
        return DriverManager.getConnection(url, user, password);
    }

    public void addVisitor(Visitor visitor) {
        String sql = "INSERT INTO visitors (name, phone, is_blacklisted) VALUES (?, ?, ?)";

        try (Connection conn = getConnection();
             PreparedStatement pstmt = conn.prepareStatement(sql)) {
            pstmt.setString(1, visitor.getName());
            pstmt.setString(2, visitor.getPhone());
            pstmt.setBoolean(3, visitor.isBlacklisted());
            pstmt.executeUpdate();
        } catch (SQLException e) {
            e.printStackTrace();
        }
    }

    public Visitor getVisitor(String phone) {
        String sql = "SELECT * FROM visitors WHERE phone = ?";

        try (Connection conn = getConnection();
             PreparedStatement pstmt = conn.prepareStatement(sql)) {
            pstmt.setString(1, phone);
            ResultSet rs = pstmt.executeQuery();

            if (rs.next()) {
                String name = rs.getString("name");
                boolean isBlacklisted = rs.getBoolean("is_blacklisted");
                Visitor visitor = new Visitor(name, phone, isBlacklisted);
                return visitor;
            }
        } catch (SQLException e) {
            e.printStackTrace();
        }
        return null;
    }

    public void updateVisitor(Visitor visitor) {
        String sql = "UPDATE visitors SET is_blacklisted = ? WHERE phone = ?";

        try (Connection conn = getConnection();
             PreparedStatement pstmt = conn.prepareStatement(sql)) {
            pstmt.setBoolean(1, visitor.isBlacklisted());
            pstmt.setString(2, visitor.getPhone());
            pstmt.executeUpdate();
        } catch (SQLException e) {
            e.printStackTrace();
        }
    }

    public void deleteVisitor(String phone) {
        String sql = "DELETE FROM visitors WHERE phone = ?";

        try (Connection conn = getConnection();
             PreparedStatement pstmt = conn.prepareStatement(sql)) {
            pstmt.setString(1, phone);
            pstmt.executeUpdate();
        } catch (SQLException e) {
            e.printStackTrace();
        }
    }
}

3. 创建一个VisitorManagementSystem类，用于管理访客和黑名单。

import java.util.Scanner;

public class VisitorManagementSystem {
    private VisitorDAO visitorDAO;

    public VisitorManagementSystem() {
        visitorDAO = new VisitorDAO();
    }

    public void addVisitor() {
        Scanner scanner = new Scanner(System.in);
        System.out.print("Enter visitor name: ");
        String name = scanner.nextLine();
        System.out.print("Enter visitor phone: ");
        String phone = scanner.nextLine();
        Visitor visitor = new Visitor(name, phone, false);
        visitorDAO.addVisitor(visitor);
    }

    public void searchVisitor() {
        Scanner scanner = new Scanner(System.in);
        System.out.print("Enter visitor phone: ");
        String phone = scanner.nextLine();
        Visitor visitor = visitorDAO.getVisitor(phone);

        if (visitor != null) {
            System.out.println("Name: " + visitor.getName());
            System.out.println("Phone: " + visitor.getPhone());
            System.out.println("Blacklisted: " + visitor.isBlacklisted());
        } else {
            System.out.println("Visitor not found.");
        }
    }

    public void updateVisitor() {
        Scanner scanner = new Scanner(System.in);
        System.out.print("Enter visitor phone: ");
        String phone = scanner.nextLine();
        Visitor visitor = visitorDAO.getVisitor(phone);

        if (visitor != null) {
            System.out.println("Name: " + visitor.getName());
            System.out.println("Phone: " + visitor.getPhone());
            System.out.println("Blacklisted: " + visitor.isBlacklisted());
            System.out.print("Is blacklisted? (true/false): ");
            boolean isBlacklisted = scanner.nextBoolean();
            visitor.setBlacklisted(isBlacklisted);
            visitorDAO.updateVisitor(visitor);
        } else {
            System.out.println("Visitor not found.");
        }
    }

    public void deleteVisitor() {
        Scanner scanner = new Scanner(System.in);
        System.out.print("Enter visitor phone: ");
        String phone = scanner.nextLine();
        visitorDAO.deleteVisitor(phone);
    }

    public static void main(String[] args) {
        VisitorManagementSystem system = new VisitorManagementSystem();
        Scanner scanner = new Scanner(System.in);

        while (true) {
            System.out.println("1. Add visitor");
            System.out.println("2. Search visitor");
            System.out.println("3. Update visitor");
            System.out.println("4. Delete visitor");
            System.out.println("5. Exit");
            System.out.print("Enter your choice: ");
            int choice = scanner.nextInt();

            switch (choice) {
                case 1:
                    system.addVisitor();
                    break;
                case 2:
                    system.searchVisitor();
                    break;
                case 3:
                    system.updateVisitor();
                    break;
                case 4:
                    system.deleteVisitor();
                    break;
                case 5:
                    System.exit(0);
                    break;
                default:
                    System.out.println("Invalid choice.");
            }
        }
    }
}

4. 创建一个MySQL数据库，名为visitor_management_system。其中包含一个名为visitors的表，存储访客的姓名、电话和是否在黑名单中的状态。

CREATE DATABASE IF NOT EXISTS visitor_management_system;

USE visitor_management_system;

CREATE TABLE IF NOT EXISTS visitors (
    name VARCHAR(255) NOT NULL,
    phone VARCHAR(20) NOT NULL PRIMARY KEY,
    is_blacklisted BOOLEAN NOT NULL DEFAULT false
);

在上述代码中，创建了一个访客类Visitor，包含访客的姓名、电话和是否在黑名单中的状态。创建了一个VisitorDAO类，处理与访客数据库的交互。在VisitorDAO类中，使用了JDBC连接MySQL数据库的方法，包含增加访客、查找访客、更新访客和删除访客的方法。创建了一个VisitorManagementSystem类，用于管理访客和黑名单。在VisitorManagementSystem类中，使用了Scanner类来获取用户输入，包含添加访客、查找访客、更新访客和删除访客的方法。最后创建了一个MySQL数据库，名为visitor_management_system，其中包含一个名为visitors的表，存储访客的姓名、电话和是否在黑名单中的状态。

以上是访客管理系统的详细代码和解释。