用Java代码创建一个图书管理系统，要求有增加功能，查询功能，删除功能，修改功能，登录功能，异常处理机制

好的，我可以帮您提供一个简单的 Java 代码示例：

import java.sql.*;
import java.util.Scanner;

public class BookManagementSystem {
    private static final String DB_URL = "jdbc:mysql://localhost:3306/bookdb";
    private static final String DB_USER = "root";
    private static final String DB_PASSWORD = "password";
    private static Connection conn = null;
    private static PreparedStatement pstmt = null;
    private static ResultSet rs = null;
    private static Scanner scanner = new Scanner(System.in);

    public static void main(String[] args) {
        try {
            conn = DriverManager.getConnection(DB_URL, DB_USER, DB_PASSWORD);
            System.out.println("连接数据库成功！");
            login();
        } catch (SQLException e) {
            System.out.println("连接数据库失败：" + e.getMessage());
        }
    }

    private static void login() {
        System.out.print("请输入用户名：");
        String username = scanner.nextLine();
        System.out.print("请输入密码：");
        String password = scanner.nextLine();
        if (username.equals("admin") && password.equals("admin")) {
            System.out.println("登录成功！");
            showMenu();
        } else {
            System.out.println("用户名或密码错误，请重新登录！");
            login();
        }
    }

    private static void showMenu() {
        System.out.println("请选择要执行的操作：");
        System.out.println("1. 添加图书");
        System.out.println("2. 查询图书");
        System.out.println("3. 删除图书");
        System.out.println("4. 修改图书");
        System.out.println("5. 退出系统");
        int choice = scanner.nextInt();
        scanner.nextLine(); // 消耗掉输入的回车符
        switch (choice) {
            case 1:
                addBook();
                break;
            case 2:
                queryBook();
                break;
            case 3:
                deleteBook();
                break;
            case 4:
                updateBook();
                break;
            case 5:
                System.out.println("感谢使用图书管理系统！");
                System.exit(0);
            default:
                System.out.println("输入有误，请重新选择要执行的操作！");
                showMenu();
        }
    }

    private static void addBook() {
        try {
            System.out.print("请输入书名：");
            String title = scanner.nextLine();
            System.out.print("请输入作者：");
            String author = scanner.nextLine();
            System.out.print("请输入出版日期（格式为 yyyy-MM-dd）：");
            String pubDate = scanner.nextLine();
            System.out.print("请输入出版社：");
            String publisher = scanner.nextLine();
            System.out.print("请输入ISBN：");
            String isbn = scanner.nextLine();
            String sql = "INSERT INTO book(title, author, pub_date, publisher, isbn) VALUES (?, ?, ?, ?, ?)";
            pstmt = conn.prepareStatement(sql);
            pstmt.setString(1, title);
            pstmt.setString(2, author);
            pstmt.setString(3, pubDate);
            pstmt.setString(4, publisher);
            pstmt.setString(5, isbn);
            int result = pstmt.executeUpdate();
            if (result > 0) {
                System.out.println("添加图书成功！");
            } else {
                System.out.println("添加图书失败！");
            }
            showMenu();
        } catch (SQLException e) {
            System.out.println("添加图书失败：" + e.getMessage());
        }
    }

    private static void queryBook() {
        try {
            System.out.print("请输入要查询的书名或作者关键字：");
            String keyword = scanner.nextLine();
            String sql = "SELECT * FROM book WHERE title LIKE ? OR author LIKE ?";
            pstmt = conn.prepareStatement(sql);
            pstmt.setString(1, "%" + keyword + "%");
            pstmt.setString(2, "%" + keyword + "%");
            rs = pstmt.executeQuery();
            if (rs.next()) {
                System.out.println("查询结果如下：");
                System.out.println("书名\t作者\t出版日期\t出版社\tISBN");
                do {
                    String title = rs.getString("title");
                    String author = rs.getString("author");
                    String pubDate = rs.getString("pub_date");
                    String publisher = rs.getString("publisher");
                    String isbn = rs.getString("isbn");
                    System.out.println(title + "\t" + author + "\t" + pubDate + "\t" + publisher + "\t" + isbn);
                } while (rs.next());
            } else {
                System.out.println("没有查询到相关图书！");
            }
            showMenu();
        } catch (SQLException e) {
            System.out.println("查询图书失败：" + e.getMessage());
        }
    }

    private static void deleteBook() {
        try {
            System.out.print("请输入要删除的图书的ISBN：");
            String isbn = scanner.nextLine();
            String sql = "DELETE FROM book WHERE isbn = ?";
            pstmt = conn.prepareStatement(sql);
            pstmt.setString(1, isbn);
            int result = pstmt.executeUpdate();
            if (result > 0) {
                System.out.println("删除图书成功！");
            } else {
                System.out.println("删除图书失败！");
            }
            showMenu();
        } catch (SQLException e) {
            System.out.println("删除图书失败：" + e.getMessage());
        }
    }

    private static void updateBook() {
        try {
            System.out.print("请输入要修改的图书的ISBN：");
            String isbn = scanner.nextLine();
            String sql = "SELECT * FROM book WHERE isbn = ?";
            pstmt = conn.prepareStatement(sql);
            pstmt.setString(1, isbn);
            rs = pstmt.executeQuery();
            if (rs.next()) {
                System.out.print("请输入新的书名（原书名为 " + rs.getString("title") + "）：");
                String title = scanner.nextLine();
                System.out.print("请输入新的作者（原作者为 " + rs.getString("author") + "）：");
                String author = scanner.nextLine();
                System.out.print("请输入新的出版日期（格式为 yyyy-MM-dd，原出版日期为 " + rs.getString("pub_date") + "）：");
                String pubDate = scanner.nextLine();
                System.out.print("请输入新的出版社（原出版社为 " + rs.getString("publisher") + "）：");
                String publisher = scanner.nextLine();
                sql = "UPDATE book SET title = ?, author = ?, pub_date = ?, publisher = ? WHERE isbn = ?";
                pstmt = conn.prepareStatement(sql);
                pstmt.setString(1, title);
                pstmt.setString(2, author);
                pstmt.setString(3, pubDate);
                pstmt.setString(4, publisher);
                pstmt.setString(5, isbn);
                int result = pstmt.executeUpdate();
                if (result > 0) {
                    System.out.println("修改图书成功！");
                } else {
                    System.out.println("修改图书失败！");
                }
            } else {
                System.out.println("没有找到要修改的图书！");
            }
            showMenu();
        } catch (SQLException e) {
            System.out.println("修改图书失败：" + e.getMessage());
        }
    }
}

这个代码示例实现了以下功能：

1. 连接 MySQL 数据库；
2. 提供登录功能；
3. 提供菜单功能，用户可以选择要执行的操作；
4. 实现添加图书、查询图书、删除图书、修改图书等功能；
5. 对异常进行了简单的处理。

当然，这个代码示例还有很多不足之处，您可以根据自己的需求进行修改和完善。