Java のシャットダウン フックとは何ですか?また、それを効果的に使用するにはどうすればよいですか?

public class ShutdownHookExample {
    public static void main(String[] args) {
        // Create a new thread for the shutdown hook
        Thread shutdownHook = new Thread(() -> {
            System.out.println("Shutdown Hook is running...");
            // Perform any cleanup here
        });

        // Register the shutdown hook
        Runtime.getRuntime().addShutdownHook(shutdownHook);

        // Simulate some work
        System.out.println("Application is running...");
        try {
            Thread.sleep(5000); // Sleep for 5 seconds
        } catch (InterruptedException e) {
            Thread.currentThread().interrupt();
        }

        System.out.println("Application is ending...");
    }
}

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

public class DatabaseShutdownHookExample {
    private static Connection connection;

    public static void main(String[] args) {
        try {
            // Initialize database connection
            connection = DriverManager.getConnection("jdbc:mysql://localhost:3306/mydatabase", "user", "password");

            // Register shutdown hook to close the connection
            Runtime.getRuntime().addShutdownHook(new Thread(() -> {
                try {
                    if (connection != null && !connection.isClosed()) {
                        connection.close();
                        System.out.println("Database connection closed.");
                    }
                } catch (SQLException e) {
                    e.printStackTrace();
                }
            }));

            // Simulate application work
            System.out.println("Application is running...");
            Thread.sleep(5000); // Sleep for 5 seconds

        } catch (SQLException | InterruptedException e) {
            e.printStackTrace();
        }
    }
}

import java.io.FileWriter;
import java.io.IOException;

public class StateShutdownHookExample {
    public static void main(String[] args) {
        // Register a shutdown hook to save state to a file
        Runtime.getRuntime().addShutdownHook(new Thread(() -> {
            try (FileWriter writer = new FileWriter("app_state.txt")) {
                writer.write("Application state saved on shutdown.");
                System.out.println("Application state saved.");
            } catch (IOException e) {
                e.printStackTrace();
            }
        }));

        // Simulate application work
        System.out.println("Application is running...");
        try {
            Thread.sleep(5000); // Sleep for 5 seconds
        } catch (InterruptedException e) {
            Thread.currentThread().interrupt();
        }
    }
}