JustOneLock.java Source code

Introduction

Here is the source code for JustOneLock.java

Source

import java.io.File;
import java.io.RandomAccessFile;
import java.nio.channels.FileChannel;
import java.nio.channels.FileLock;

class JustOneLock {
    private String appName;

    FileLock lock;

    FileChannel channel;

    public JustOneLock(String appName) {
        this.appName = appName;
    }

    public boolean isAppActive() throws Exception {
        File file = new File(System.getProperty("user.home"), appName + ".tmp");
        channel = new RandomAccessFile(file, "rw").getChannel();

        lock = channel.tryLock();
        if (lock == null) {
            lock.release();
            channel.close();
            return true;
        }
        Runtime.getRuntime().addShutdownHook(new Thread() {
            public void run() {
                try {
                    lock.release();
                    channel.close();
                } catch (Exception e) {
                    e.printStackTrace();
                }
            }
        });
        return false;
    }
}

public class Main {
    public static void main(String[] args) throws Exception {
        JustOneLock ua = new JustOneLock("JustOneId");
        if (ua.isAppActive()) {
            System.out.println("Already active.");
            System.exit(1);
        } else {
            System.out.println("NOT already active.");
        }
    }
}