Java并发编程之如何优雅关闭钩子Shutdown Hook

public class HookThreadDemo {
    privatestaticclass HookRunnable implements Runnable {
        @Override
        public void run() {
            try {
                System.out.println("钩子线程 " + Thread.currentThread().getName() + " 正在执行...");
                Thread.sleep(2000L);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
            System.out.println("钩子线程 " + Thread.currentThread().getName() + " 执行结束");
        }
    }

    public static void main(String[] args) {
        HookRunnable hookRunnable = new HookRunnable();
        // 添加钩子线程 0
        Runtime.getRuntime().addShutdownHook(new Thread(hookRunnable));
        // 添加钩子线程 1
        Runtime.getRuntime().addShutdownHook(new Thread(hookRunnable));
        System.out.println("主线程即将结束执行");
    }
}

public class DatabaseConnection {
    privatestatic Connection conn;

    public static void main(String[] args) {
        System.out.println("主线程开始执行");
        initConnection(); // 初始化数据库连接
        System.out.println("执行数据查询与处理");

        // 注册关闭钩子
        Runtime.getRuntime().addShutdownHook(new Thread(() -> closeConnection()));
        System.out.println("主线程结束执行");
    }

    private static void initConnection() {
        try {
            Class.forName("com.mysql.cj.jdbc.Driver");
            conn = DriverManager.getConnection(
                "jdbc:mysql://localhost:3306/school_info?useSSL=true&",
                "root", "root"
            );
            System.out.println("数据库连接成功！");
        } catch (ClassNotFoundException | SQLException e) {
            e.printStackTrace();
        }
    }

    private static void closeConnection() {
        try {
            conn.close();
            System.out.println("数据库连接已关闭！");
        } catch (SQLException e) {
            e.printStackTrace();
        }
    }
}

public void registerShutdownHook() {
    if (this.shutdownHook == null) {
        this.shutdownHook = new Thread(() -> doClose());
        Runtime.getRuntime().addShutdownHook(this.shutdownHook);
    }
}

public void registerShutdownHook() {
    if (this.shutdownHook == null) {
        this.shutdownHook = new Thread(() -> {
            synchronized (startupShutdownMonitor) {
                doClose();
            }
        });
        Runtime.getRuntime().addShutdownHook(this.shutdownHook);
    }
}

public class SignalHandlerTest implements SignalHandler {
    public static void main(String[] args) {
        Runtime.getRuntime().addShutdownHook(new Thread(() -> 
            System.out.println("关闭钩子正在运行...")));

        SignalHandler handler = new SignalHandlerTest();
        Signal.handle(new Signal("INT"), handler);  // 捕获 Ctrl+C
        Signal.handle(new Signal("TERM"), handler); // 捕获 kill 命令

        while (true) {
            System.out.println("主线程运行中...");
            Thread.sleep(2000);
        }
    }

    @Override
    public void handle(Signal signal) {
        System.out.println("接收到信号：" + signal.getName() + "-" + signal.getNumber());
        System.exit(0);
    }
}