AppLocker

AppLocker is a small library which provides the often missing single instance functionality.

Features

• Safe: based on file channel locking, lock will be released even in case of power outage
• An arbitrary AppLocker can send a string message to the AppLocker which currently owns the lock
• Lightweight
• No transitive dependencies
• JDK 11+ support
• Logging via System.Logger

Quick Start

AppLocker locker = AppLocker.create("my-app")
        .setMessageHandler(file -> open(file))  // optional: answer messages from other instances
        .build();

if (!locker.tryLock()) {
    // another instance is running: pass it the file and exit
    locker.sendMessage(file);
    System.exit(0);
}

AppLocker.Builder options, all optional:

• setPath(Path): directory for the lock files (default: working directory)
• setIdEncoder(LockIdEncoder): maps the id to a file name (default: SHA-1)
• setMessageHandler(MessageHandler): enables messaging (default: none)
• setMessageTimeout(Duration): how long sendMessage waits for the answer (default: 30 seconds)

I/O errors are reported as LockingException.

More details can be found in JavaDocs.

Download

Maven:

<dependency>
    <groupId>io.github.sanyarnd</groupId>
    <artifactId>app-locker</artifactId>
    <version>2.0.0</version>
</dependency>

Gradle:

implementation("io.github.sanyarnd:app-locker:2.0.0")

Jars are also available in GitHub Packages and on the releases page.

Building

Requires JDK 25:

./gradlew build
./gradlew spotlessApply

Releasing

Pushing a tag like 2.0.0 publishes to Maven Central and GitHub Packages, creates a GitHub release and updates the site.

Secrets: MAVEN_CENTRAL_USERNAME, MAVEN_CENTRAL_PASSWORD (Central Portal token), GPG_PRIVATE_KEY, GPG_KEY_PASSPHRASE.

Changelog

See CHANGELOG.md.