从零开始手写JDBC连接数据库的详细指南

<dependency>
    <groupId>mysql</groupId>
    <artifactId>mysql-connector-java</artifactId>
    <version>8.0.33</version> <!-- 使用最新稳定版本 -->
</dependency>

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

-- 创建数据库
CREATE DATABASE IF NOT EXISTS demo_db CHARACTER SET utf8mb4 COLLATE utf8mb4_unicode_ci;

-- 使用数据库
USE demo_db;

-- 创建用户表
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
);

-- 插入测试数据
INSERT INTO users (name, email) VALUES
('张三', 'zhangsan@example.com'),
('李四', 'lisi@example.com'),
('王五', 'wangwu@example.com');

import java.sql.*;

/**
 * 手写JDBC连接数据库示例
 * 演示连接MySQL、查询、插入操作
 */
public class JDBCDemo {

    // 数据库连接信息 - 请根据实际情况修改
    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"; // 替换为你的MySQL用户名
    private static final String PASSWORD = "your_password"; // 替换为你的MySQL密码

    // JDBC驱动类名 (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 {
            // ========== 步骤1：加载JDBC驱动 (可选，现代JDBC通常自动加载) ==========
            // 显式加载驱动类，确保驱动被注册到DriverManager
            // 对于JDBC 4.0+ (Java 6+)，通常不需要这一步，驱动会自动发现和加载
            // 但显式加载可以确保兼容性或在特定环境下工作
            Class.forName(DRIVER_CLASS);
            System.out.println("JDBC驱动加载成功！");

            // ========== 步骤2：建立数据库连接 ==========
            System.out.println("正在连接数据库...");
            connection = DriverManager.getConnection(DB_URL, USER, PASSWORD);
            System.out.println("数据库连接成功！");

            // ========== 步骤3：创建Statement对象 ==========
            statement = connection.createStatement();

            // ========== 步骤4：执行查询SQL并处理结果 ==========
            System.out.println("\n--- 查询所有用户信息 ---");
            String selectSql = "SELECT id, name, email, created_at FROM users";
            resultSet = statement.executeQuery(selectSql); // executeQuery用于SELECT

            // 处理ResultSet
            System.out.printf("%-5s %-15s %-25s %-20s%n", "ID", "姓名", "邮箱", "创建时间");
            System.out.println("------------------------------------------------------------");
            while (resultSet.next()) {
                int id = resultSet.getInt("id"); // 根据列名获取int值
                String name = resultSet.getString("name"); // 根据列名获取String值
                String email = resultSet.getString("email");
                Timestamp createdAt = resultSet.getTimestamp("created_at");

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

            // ========== 步骤5：使用PreparedStatement执行插入操作 (防止SQL注入) ==========
            System.out.println("\n--- 准备插入新用户 ---");
            String insertSql = "INSERT INTO users (name, email) VALUES (?, ?)";
            preparedStatement = connection.prepareStatement(insertSql); // 使用PreparedStatement

            // 设置参数值 (索引从1开始)
            preparedStatement.setString(1, "赵六");
            preparedStatement.setString(2, "zhaoliu@example.com");

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

            // ========== 步骤6：再次查询，验证插入结果 ==========
            System.out.println("\n--- 再次查询所有用户信息 (验证插入) ---");
            // 重新执行查询
            resultSet.close(); // 关闭之前的ResultSet
            resultSet = statement.executeQuery(selectSql);

            System.out.printf("%-5s %-15s %-25s %-20s%n", "ID", "姓名", "邮箱", "创建时间");
            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驱动类未找到！请检查驱动JAR是否在类路径中。");
            e.printStackTrace();
        } catch (SQLException e) {
            System.err.println("数据库操作发生错误！");
            e.printStackTrace();
        } finally {
            // ========== 步骤7：关闭资源 (非常重要！) ==========
            // 必须在finally块中关闭，确保即使发生异常也能释放资源
            // 关闭顺序：ResultSet -> Statement/PreparedStatement -> Connection
            try {
                if (resultSet != null) {
                    resultSet.close();
                    System.out.println("ResultSet已关闭。");
                }
            } catch (SQLException e) {
                System.err.println("关闭ResultSet时出错！");
                e.printStackTrace();
            }

            try {
                if (statement != null) {
                    statement.close();
                    System.out.println("Statement已关闭。");
                }
            } catch (SQLException e) {
                System.err.println("关闭Statement时出错！");
                e.printStackTrace();
            }

            try {
                if (preparedStatement != null) {
                    preparedStatement.close();
                    System.out.println("PreparedStatement已关闭。");
                }
            } catch (SQLException e) {
                System.err.println("关闭PreparedStatement时出错！");
                e.printStackTrace();
            }

            try {
                if (connection != null) {
                    connection.close();
                    System.out.println("数据库连接已关闭。");
                }
            } catch (SQLException e) {
                System.err.println("关闭Connection时出错！");
                e.printStackTrace();
            }
        }

        System.out.println("JDBC演示程序结束。");
    }
}