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'databene commons' is an open source Java library by Volker Bergmann.
It provides extensions to the Java core library by utility classes, abstract concepts
and concrete implementations.
/*
* Copyright (C) 2004-2014 Volker Bergmann ([email protected]).
* All rights reserved.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
* http://www.apache.org/licenses/LICENSE-2.0
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.databene.commons.file;
import java.io.File;
import java.io.IOException;
/**
* Utility for preventing the start of more than one process of a given application.
* The lock is acquired calling {@link #acquireLock(String)} with a file name.
* The method creates the file and registers a shutdown hook that deletes the file
* when the process finishes. When a second acquireLock is tried while the file exists
* (no matter if by this or another process), a {@link LockAlreadyAcquiredException}
* is thrown.
* It can be used like this:
*
* try {
* LockFile.acquireLock("MyApp.lock");
* } catch (LockFile.LockAlreadyAcquiredException e) {
* JOptionPane.showMessageDialog(null, "MyApp is already running", "Error", JOptionPane.ERROR_MESSAGE);
* System.exit(-1);
* }
*
*
* Created: 29.11.2013 08:16:23
* @since 0.5.25
* @author Volker Bergmann
*/
public class LockFile {
public static void acquireLock(String fileName) throws LockAlreadyAcquiredException {
final File lockFile = new File(fileName);
if (lockFile.exists()) {
throw new LockAlreadyAcquiredException(fileName);
} else {
try {
File parent = lockFile.getParentFile();
parent.mkdirs();
lockFile.createNewFile();
} catch (IOException e) {
throw new RuntimeException(e);
}
Runtime.getRuntime().addShutdownHook(new Thread() {
@Override
public void run() {
lockFile.delete();
}
});
}
}
public static class LockAlreadyAcquiredException extends Exception {
private static final long serialVersionUID = 1L;
public LockAlreadyAcquiredException(String fileName) {
super("Lock file already acquired: " + fileName);
}
}
}