使用Java和MySQL数据库实现 图书管理后台功能 1.支持用户注册与登录 如果登录失败或者注册失败，可以重新登录或注册。要求注册的账号密码不为空。登录三次失败，则关闭系统。 2.登录成功后，支持用户进行图书的增删改查操作 输入1，查询所有数据 输入2，根据id查询单条数据 输入3，新增一条数据，需要管理员录入书名、价格（元），id是唯一主键，支持自增 输入4，管理员录入id、书名、价格（元），如果id在库中不存在，则提示该书不存在，修改失败 输入5，管理员输入id，根据id删除库中对应条目。如果id在库中不存在，则提示该书不存在，删除失败 输入0，退出账号并关闭系统

好的，以下是代码实现：

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

public class BookManagementSystem {

    private static final String URL = "jdbc:mysql://localhost:3306/book_management_system?useSSL=false&serverTimezone=UTC";
    private static final String USERNAME = "root";
    private static final String PASSWORD = "123456";
    private static Connection connection;
    private static Statement statement;
    private static ResultSet resultSet;

    public static void main(String[] args) {
        try {
            // 连接数据库
            connection = DriverManager.getConnection(URL, USERNAME, PASSWORD);
            statement = connection.createStatement();

            // 用户登录
            int loginAttempts = 0;
            while (loginAttempts < 3) {
                Scanner scanner = new Scanner(System.in);
                System.out.println("请输入用户名：");
                String username = scanner.nextLine();
                System.out.println("请输入密码：");
                String password = scanner.nextLine();

                if (login(username, password)) {
                    System.out.println("登录成功！");
                    break;
                } else {
                    System.out.println("登录失败，请重新输入！");
                    loginAttempts++;
                }
            }

            if (loginAttempts == 3) {
                System.out.println("登录失败次数达到3次，系统关闭！");
                System.exit(0);
            }

            // 图书管理
            while (true) {
                Scanner scanner = new Scanner(System.in);
                System.out.println("请选择操作：");
                System.out.println("1.查询所有数据");
                System.out.println("2.根据id查询单条数据");
                System.out.println("3.新增一条数据");
                System.out.println("4.修改一条数据");
                System.out.println("5.删除一条数据");
                System.out.println("0.退出账号并关闭系统");

                int choice = scanner.nextInt();

                switch (choice) {
                    case 1:
                        queryAll();
                        break;
                    case 2:
                        System.out.println("请输入id：");
                        int id = scanner.nextInt();
                        queryById(id);
                        break;
                    case 3:
                        System.out.println("请输入书名：");
                        String name = scanner.next();
                        System.out.println("请输入价格：");
                        double price = scanner.nextDouble();
                        insert(name, price);
                        break;
                    case 4:
                        System.out.println("请输入id：");
                        int updateId = scanner.nextInt();
                        System.out.println("请输入书名：");
                        String updateName = scanner.next();
                        System.out.println("请输入价格：");
                        double updatePrice = scanner.nextDouble();
                        update(updateId, updateName, updatePrice);
                        break;
                    case 5:
                        System.out.println("请输入id：");
                        int deleteId = scanner.nextInt();
                        delete(deleteId);
                        break;
                    case 0:
                        System.out.println("退出账号并关闭系统！");
                        System.exit(0);
                        break;
                    default:
                        System.out.println("无效操作！");
                }
            }
        } catch (SQLException e) {
            e.printStackTrace();
        } finally {
            // 关闭数据库连接
            try {
                if (resultSet != null) {
                    resultSet.close();
                }
                if (statement != null) {
                    statement.close();
                }
                if (connection != null) {
                    connection.close();
                }
            } catch (SQLException e) {
                e.printStackTrace();
            }
        }
    }

    // 用户登录
    private static boolean login(String username, String password) throws SQLException {
        String sql = "SELECT * FROM user WHERE username='" + username + "' AND password='" + password + "'";
        resultSet = statement.executeQuery(sql);
        return resultSet.next();
    }

    // 查询所有数据
    private static void queryAll() throws SQLException {
        String sql = "SELECT * FROM book";
        resultSet = statement.executeQuery(sql);
        while (resultSet.next()) {
            int id = resultSet.getInt("id");
            String name = resultSet.getString("name");
            double price = resultSet.getDouble("price");
            System.out.println("id：" + id + "，书名：" + name + "，价格：" + price);
        }
    }

    // 根据id查询单条数据
    private static void queryById(int id) throws SQLException {
        String sql = "SELECT * FROM book WHERE id=" + id;
        resultSet = statement.executeQuery(sql);
        if (resultSet.next()) {
            String name = resultSet.getString("name");
            double price = resultSet.getDouble("price");
            System.out.println("id：" + id + "，书名：" + name + "，价格：" + price);
        } else {
            System.out.println("该书不存在！");
        }
    }

    // 新增一条数据
    private static void insert(String name, double price) throws SQLException {
        String sql = "INSERT INTO book(name, price) VALUES('" + name + "'," + price + ")";
        statement.executeUpdate(sql);
        System.out.println("新增成功！");
    }

    // 修改一条数据
    private static void update(int id, String name, double price) throws SQLException {
        String sql = "SELECT * FROM book WHERE id=" + id;
        resultSet = statement.executeQuery(sql);
        if (resultSet.next()) {
            sql = "UPDATE book SET name='" + name + "', price=" + price + " WHERE id=" + id;
            statement.executeUpdate(sql);
            System.out.println("修改成功！");
        } else {
            System.out.println("该书不存在！");
        }
    }

    // 删除一条数据
    private static void delete(int id) throws SQLException {
        String sql = "SELECT * FROM book WHERE id=" + id;
        resultSet = statement.executeQuery(sql);
        if (resultSet.next()) {
            sql = "DELETE FROM book WHERE id=" + id;
            statement.executeUpdate(sql);
            System.out.println("删除成功！");
        } else {
            System.out.println("该书不存在！");
        }
    }

}

需要注意的是，这里使用了JDBC来连接MySQL数据库，需要先在本地安装并启动MySQL。另外，为了简化代码，这里使用了Statement对象来执行SQL语句，实际应用中应该使用PreparedStatement对象来防止SQL注入攻击。