Often we want to make sure that only 1 instance our application running.
Because something terrible could happen when more than 1 instance running (for example the whole server would exploded and that would make you fired 
)
Nevertheless what the reason, one of the way to make this happen is by creating a lock file as a sign that an instance is currently running.
So you application will have this flow:
- Check if the lock file exists.
- Try to delete the lock file to check if there’s really a running process lock the file.
- Get the file lock.
- If failed to get the lock file, show error that there’s already an instance running
- If successfully get the lock then go on with your application want to do.
- When application ended/closed release the lock and delete the file lock.
package test.jimmy.filelock; import java.io.File; import java.io.IOException; import java.io.RandomAccessFile; import java.nio.channels.FileChannel; import java.nio.channels.FileLock; public class MyApp { private static File f; private static FileChannel channel; private static FileLock lock; public static void main(String[] args) { try { f = new File("RingOnRequest.lock"); // Check if the lock exist if (f.exists()) { // if exist try to delete it f.delete(); } // Try to get the lock channel = new RandomAccessFile(f, "rw").getChannel(); lock = channel.tryLock(); if(lock == null) { // File is lock by other application channel.close(); throw new RuntimeException("Only 1 instance of MyApp can run."); } // Add shutdown hook to release lock when application shutdown ShutdownHook shutdownHook = new ShutdownHook(); Runtime.getRuntime().addShutdownHook(shutdownHook); //Your application tasks here.. System.out.println("Running"); try { Thread.sleep(10000); } catch (InterruptedException e) { e.printStackTrace(); } catch(IOException e) { throw new RuntimeException("Could not start process.", e); } } public static void unlockFile() { // release and delete file lock try { if(lock != null) lock.release(); channel.close(); f.delete(); } catch(IOException e) { e.printStackTrace(); } } static class ShutdownHook extends Thread { public void run() { unlockFile(); } } } |
Technorati Tags: java, file lock, shutdownhook, lock, single, one, intance