<dependency>
    <groupId>mysql</groupId>
    <artifactId>mysql-connector-java</artifactId>
    <version>8.0.33</version> <!-- 使用最新穩(wěn)定版本 -->
</dependency>

implementation 'mysql:mysql-connector-java:8.0.33'

-- 創(chuàng)建數(shù)據(jù)庫
CREATE DATABASE IF NOT EXISTS demo_db CHARACTER SET utf8mb4 COLLATE utf8mb4_unicode_ci;

-- 使用數(shù)據(jù)庫
USE demo_db;

-- 創(chuàng)建用戶表
CREATE TABLE IF NOT EXISTS users (
    id INT AUTO_INCREMENT PRIMARY KEY,
    name VARCHAR(100) NOT NULL,
    email VARCHAR(150) UNIQUE NOT NULL,
    created_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP
);

-- 插入測試數(shù)據(jù)
INSERT INTO users (name, email) VALUES
('張三', 'zhangsan@example.com'),
('李四', 'lisi@example.com'),
('王五', 'wangwu@example.com');

import java.sql.*;

/**
 * 手寫JDBC連接數(shù)據(jù)庫示例
 * 演示連接MySQL、查詢、插入操作
 */
public class JDBCDemo {

    // 數(shù)據(jù)庫連接信息 - 請根據(jù)實際情況修改
    private static final String DB_URL = "jdbc:mysql://localhost:3306/demo_db?useSSL=false&serverTimezone=UTC&useUnicode=true&characterEncoding=utf8";
    private static final String USER = "your_username"; // 替換為你的MySQL用戶名
    private static final String PASSWORD = "your_password"; // 替換為你的MySQL密碼

    // JDBC驅(qū)動類名 (MySQL 8.0+)
    private static final String DRIVER_CLASS = "com.mysql.cj.jdbc.Driver";

    public static void main(String[] args) {
        Connection connection = null;
        Statement statement = null;
        ResultSet resultSet = null;
        PreparedStatement preparedStatement = null;

        try {
            // ========== 步驟1：加載JDBC驅(qū)動 (可選，現(xiàn)代JDBC通常自動加載) ==========
            // 顯式加載驅(qū)動類，確保驅(qū)動被注冊到DriverManager
            // 對于JDBC 4.0+ (Java 6+)，通常不需要這一步，驅(qū)動會自動發(fā)現(xiàn)和加載
            // 但顯式加載可以確保兼容性或在特定環(huán)境下工作
            Class.forName(DRIVER_CLASS);
            System.out.println("JDBC驅(qū)動加載成功！");

            // ========== 步驟2：建立數(shù)據(jù)庫連接 ==========
            System.out.println("正在連接數(shù)據(jù)庫...");
            connection = DriverManager.getConnection(DB_URL, USER, PASSWORD);
            System.out.println("數(shù)據(jù)庫連接成功！");

            // ========== 步驟3：創(chuàng)建Statement對象 ==========
            statement = connection.createStatement();

            // ========== 步驟4：執(zhí)行查詢SQL并處理結(jié)果 ==========
            System.out.println("\n--- 查詢所有用戶信息 ---");
            String selectSql = "SELECT id, name, email, created_at FROM users";
            resultSet = statement.executeQuery(selectSql); // executeQuery用于SELECT

            // 處理ResultSet
            System.out.printf("%-5s %-15s %-25s %-20s%n", "ID", "姓名", "郵箱", "創(chuàng)建時間");
            System.out.println("------------------------------------------------------------");
            while (resultSet.next()) {
                int id = resultSet.getInt("id"); // 根據(jù)列名獲取int值
                String name = resultSet.getString("name"); // 根據(jù)列名獲取String值
                String email = resultSet.getString("email");
                Timestamp createdAt = resultSet.getTimestamp("created_at");

                // 格式化輸出
                System.out.printf("%-5d %-15s %-25s %-20s%n", id, name, email, createdAt);
            }

            // ========== 步驟5：使用PreparedStatement執(zhí)行插入操作 (防止SQL注入) ==========
            System.out.println("\n--- 準備插入新用戶 ---");
            String insertSql = "INSERT INTO users (name, email) VALUES (?, ?)";
            preparedStatement = connection.prepareStatement(insertSql); // 使用PreparedStatement

            // 設(shè)置參數(shù)值 (索引從1開始)
            preparedStatement.setString(1, "趙六");
            preparedStatement.setString(2, "zhaoliu@example.com");

            // 執(zhí)行插入
            int rowsAffected = preparedStatement.executeUpdate(); // executeUpdate用于INSERT, UPDATE, DELETE
            System.out.println("插入操作完成，影響了 " + rowsAffected + " 行。");

            // ========== 步驟6：再次查詢，驗證插入結(jié)果 ==========
            System.out.println("\n--- 再次查詢所有用戶信息 (驗證插入) ---");
            // 重新執(zhí)行查詢
            resultSet.close(); // 關(guān)閉之前的ResultSet
            resultSet = statement.executeQuery(selectSql);

            System.out.printf("%-5s %-15s %-25s %-20s%n", "ID", "姓名", "郵箱", "創(chuàng)建時間");
            System.out.println("------------------------------------------------------------");
            while (resultSet.next()) {
                int id = resultSet.getInt("id");
                String name = resultSet.getString("name");
                String email = resultSet.getString("email");
                Timestamp createdAt = resultSet.getTimestamp("created_at");
                System.out.printf("%-5d %-15s %-25s %-20s%n", id, name, email, createdAt);
            }

        } catch (ClassNotFoundException e) {
            System.err.println("JDBC驅(qū)動類未找到！請檢查驅(qū)動JAR是否在類路徑中。");
            e.printStackTrace();
        } catch (SQLException e) {
            System.err.println("數(shù)據(jù)庫操作發(fā)生錯誤！");
            e.printStackTrace();
        } finally {
            // ========== 步驟7：關(guān)閉資源 (非常重要！) ==========
            // 必須在finally塊中關(guān)閉，確保即使發(fā)生異常也能釋放資源
            // 關(guān)閉順序：ResultSet -> Statement/PreparedStatement -> Connection
            try {
                if (resultSet != null) {
                    resultSet.close();
                    System.out.println("ResultSet已關(guān)閉。");
                }
            } catch (SQLException e) {
                System.err.println("關(guān)閉ResultSet時出錯！");
                e.printStackTrace();
            }

            try {
                if (statement != null) {
                    statement.close();
                    System.out.println("Statement已關(guān)閉。");
                }
            } catch (SQLException e) {
                System.err.println("關(guān)閉Statement時出錯！");
                e.printStackTrace();
            }

            try {
                if (preparedStatement != null) {
                    preparedStatement.close();
                    System.out.println("PreparedStatement已關(guān)閉。");
                }
            } catch (SQLException e) {
                System.err.println("關(guān)閉PreparedStatement時出錯！");
                e.printStackTrace();
            }

            try {
                if (connection != null) {
                    connection.close();
                    System.out.println("數(shù)據(jù)庫連接已關(guān)閉。");
                }
            } catch (SQLException e) {
                System.err.println("關(guān)閉Connection時出錯！");
                e.printStackTrace();
            }
        }

        System.out.println("JDBC演示程序結(jié)束。");
    }
}