Example of a more advanced lock system in Java

Main.java

package YOUR_PACKAGE_NAME;

import java.io.File;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
import java.nio.channels.FileChannel;
import java.nio.channels.FileLock;

/**
 * Minimal reproducible example (MRE) - Example of a more advanced lock system.
 * @author Remzi Cavdar - ict@remzi.info - <a href="https://github.com/Remzi1993">@Remzi1993</a>
 */
public class Main {
    public static void main(String[] args) {
        /*
         * Prevents the user of starting multiple instances of the application.
         * This is done by creating a temporary file in the app directory.
         * The temp file should be excluded from git and is called App.lock in this example.
         */
        final File FILE = new File("App.lock");

        if (FILE.exists()) {
            System.err.println("The application is already running!");
            return;
        }

        try (
                FileOutputStream fileOutputStream = new FileOutputStream(FILE);
                FileChannel channel = fileOutputStream.getChannel();
                FileLock lock = channel.lock()
        ) {
            System.out.println("Starting application");
        } catch (FileNotFoundException e) {
            throw new RuntimeException(e);
        } catch (IOException e) {
            throw new RuntimeException(e);
        }

        /*
         * Register a shutdown hook to delete the lock file when the application is closed. Even when forcefully closed
         * with the task manager. (Tested on Windows 11 with JavaFX 19)
         */
        FILE.deleteOnExit();
        // Whatever your app is supposed to do
    }
}

Interested in a very simple file lock system? Check this gist out: https://gist.github.com/Remzi1993/f97a55054f3769a5d3d0d16597691f57