ApplicationLock.java

package net.mms_projects.copy_it;

import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.File;
import java.io.FileNotFoundException;
import java.io.FileReader;
import java.io.FileWriter;
import java.io.IOException;
import java.net.InetSocketAddress;
import java.net.ServerSocket;
import java.net.Socket;
import java.net.SocketAddress;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

public class ApplicationLock {

	private File lockFile;
	private ServerSocket server;
	private ServerThread thread;
	private boolean locked = false;
	private final Logger log = LoggerFactory.getLogger(this.getClass());

	public ApplicationLock(File path) {
		this.lockFile = new File(path, ".lock");
	}

	public void lock() throws LockException {
		log.info("Application locked");
		if (this.isLocked()) {
			throw new LockException("The app is already locked");
		}
		BufferedWriter writer = null;
		try {
			this.server = new ServerSocket(0);

			this.thread = new ServerThread();
			this.thread.setDaemon(true);
			this.thread.start();

			writer = new BufferedWriter(new FileWriter(this.lockFile));
			writer.write(Integer.toString(this.server.getLocalPort()));
		} catch (IOException e) {
			throw new LockException(e);
		} finally {
			try {
				if (writer != null) {
					writer.close();
				}
			} catch (IOException e) {
			}
		}
		this.locked = true;
	}

	public void unlock() {
		log.info("Application unlocked");
		if (!this.isLocked()) {
			return;
		}
		this.lockFile.delete();
		this.thread.interrupt();
		try {
			this.server.close();
		} catch (IOException e) {
		}
		this.locked = false;
	}

	public boolean isLocked() {
		return this.locked;
	}

	public boolean isRunning() {
		BufferedReader reader = null;
		Socket socket = null;
		try {
			if (!this.lockFile.exists()) {
				return false;
			}
			reader = new BufferedReader(new FileReader(this.lockFile));
			String content = reader.readLine();
			if (content == null) {
				return false;
			}
			SocketAddress sockaddr = new InetSocketAddress("127.0.0.1",
					Integer.parseInt(content));
			socket = new Socket();
			socket.connect(sockaddr, 100);
			if (socket.isConnected()) {
				return true;
			}
		} catch (FileNotFoundException e) {
		} catch (IOException e) {
			return false;
		} finally {
			try {
				if (reader != null) {
					reader.close();
				}
				if (socket != null) {
					socket.close();
				}
			} catch (IOException e) {
			}
		}
		return false;
	}

	public class LockException extends Exception {
		private static final long serialVersionUID = -1567053088980704966L;

		public LockException(String message) {
			super(message);
		}

		public LockException(Throwable clause) {
			super(clause);
		}
	}

	private class ServerThread extends Thread {
		@Override
		public void run() {
			log.info("Lock server thread running");
			while (true) {
				if (this.isInterrupted()) {
					log.info("Lock server thread interrupted");
					break;
				}
				try {
					if (!server.isClosed()) {
						server.accept();
					}
				} catch (IOException e) {
				}
			}
		}
	}

}