如何在Java代码中处理数据库连接异常

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.SQLException;

public class DBConnectionExample {
    // 数据库连接信息（替换为实际配置）
    private static final String DB_URL = "jdbc:mysql://localhost:3306/library?useSSL=false&serverTimezone=UTC";
    private static final String USER = "root";
    private static final String PASSWORD = "123456";
    private static final String DRIVER_CLASS = "com.mysql.cj.jdbc.Driver";

    // 获取数据库连接
    public static Connection getConnection() {
        Connection conn = null;
        try {
            // 1. 加载驱动（MySQL 8.0+可省略，但建议保留兼容低版本）
            Class.forName(DRIVER_CLASS);
            System.out.println("驱动加载成功");

            // 2. 获取连接
            conn = DriverManager.getConnection(DB_URL, USER, PASSWORD);
            System.out.println("数据库连接成功");

        } catch (ClassNotFoundException e) {
            // 处理驱动类未找到异常
            System.err.println("错误：数据库驱动类未找到！请检查驱动包是否引入。");
            e.printStackTrace(); // 打印堆栈信息（调试用）
        } catch (SQLException e) {
            // 处理数据库连接异常（细分错误类型）
            handleSQLException(e);
        }
        return conn;
    }

    // 细分处理SQLException
    private static void handleSQLException(SQLException e) {
        System.err.println("数据库连接失败！原因：");
        // SQL状态码（如1045表示密码错误，08001表示连接失败）
        String sqlState = e.getSQLState();
        switch (sqlState) {
            case "08001":
                System.err.println("无法连接到数据库服务器，请检查URL和端口是否正确。");
                break;
            case "28000":
                System.err.println("用户名或密码错误。");
                break;
            case "42000":
                System.err.println("数据库不存在或权限不足。");
                break;
            default:
                System.err.println("未知错误（SQLState: " + sqlState + "）");
        }
        e.printStackTrace(); // 打印详细错误信息
    }

    // 关闭连接（需在finally中调用）
    public static void closeConnection(Connection conn) {
        if (conn != null) {
            try {
                if (!conn.isClosed()) {
                    conn.close();
                    System.out.println("数据库连接已关闭");
                }
            } catch (SQLException e) {
                System.err.println("关闭连接失败：" + e.getMessage());
                e.printStackTrace();
            }
        }
    }

    public static void main(String[] args) {
        Connection conn = null;
        try {
            conn = getConnection();
            // 执行数据库操作（如查询、插入等）
        } finally {
            // 确保连接关闭
            closeConnection(conn);
        }
    }
}

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.SQLException;
import java.sql.Statement;

public class DBConnectionWithResources {
    private static final String DB_URL = "jdbc:mysql://localhost:3306/library?useSSL=false&serverTimezone=UTC";
    private static final String USER = "root";
    private static final String PASSWORD = "123456";

    public static void main(String[] args) {
        // 资源在try块结束后自动关闭（无需手动调用close()）
        try (Connection conn = DriverManager.getConnection(DB_URL, USER, PASSWORD);
             Statement stmt = conn.createStatement()) {

            System.out.println("连接成功，执行查询...");
            // 执行SQL示例
            stmt.executeQuery("SELECT * FROM books");

        } catch (SQLException e) {
            System.err.println("数据库操作失败：" + e.getMessage());
            e.printStackTrace();
        }
    }
}

public static Connection getConnectionWithRetry(int maxRetries, long delayMillis) {
    Connection conn = null;
    int retryCount = 0;
    while (retryCount < maxRetries) {
        try {
            conn = DriverManager.getConnection(DB_URL, USER, PASSWORD);
            System.out.println("连接成功");
            return conn;
        } catch (SQLException e) {
            retryCount++;
            System.err.println("第" + retryCount + "次连接失败，将在" + delayMillis + "ms后重试...");
            if (retryCount >= maxRetries) {
                System.err.println("达到最大重试次数，连接失败：" + e.getMessage());
                return null;
            }
            try {
                Thread.sleep(delayMillis); // 等待重试
            } catch (InterruptedException ie) {
                Thread.currentThread().interrupt(); // 恢复中断状态
                return null;
            }
        }
    }
    return null;
}