Nucleus

The all-in-one toolkit for shipping JVM desktop applications. Gradle plugin + runtime libraries + GitHub Actions — everything you need to go from ./gradlew run to a signed, notarized, auto-updating app on every store.

Compatible with any JVM application. Optimized for Compose Desktop.

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Why Nucleus?

Fast Cold Start

• JDK 25+ AOT Cache (Project Leyden) — Eliminates the JVM cold start penalty with a single Gradle flag. No GraalVM, no native-image, no compromise — your app launches almost instantly
• ProGuard — Built-in integration for release builds: obfuscation, optimization, and JAR joining
• Native library cleanup — Automatically strips non-target-platform .dll/.so/.dylib from dependency JARs, reducing app size

Distributable

• 17 packaging formats — DMG, PKG, NSIS, MSI, AppX, Portable, DEB, RPM, AppImage, Snap, Flatpak, ZIP, TAR, 7z, and more
• Store-ready outputs — Sandboxed PKG for the Mac App Store, AppX for the Microsoft Store, Snap for Snapcraft, Flatpak for Flathub — with automatic sandboxing pipelines
• Code signing & notarization — macOS (Developer ID, notarization, App Store), Windows (PFX, Azure Trusted Signing)
• Auto-update — Runtime library with SHA-512 verification, download progress, and platform-specific silent installation. Supports GitHub Releases and S3

Native

• Decorated windows — Draw anything in the title bar (icons, text, gradients) while keeping native window controls. Fork of Jewel's decorated window, without any Jewel dependency, with full Linux rework (GNOME Adwaita, KDE Breeze) and added DecoratedDialog support
• Reactive dark mode — OS-level theme listener via JNI that triggers Compose recomposition instantly. Unlike Compose's built-in isSystemInDarkTheme() which reads once and never updates
• Platform detection — Runtime APIs for OS, desktop environment (GNOME/KDE/XFCE/...), executable type (18 formats), and AOT mode
• Single instance & deep links — File-lock-based single instance enforcement with deep link forwarding between instances
• Deep links & file associations — Cross-platform protocol handlers and file type registration in one DSL block

CI/CD Ready

Action	Description
setup-nucleus	Sets up JBR + all packaging tools on any runner (Linux, macOS, Windows)
build-macos-universal	Merges arm64 + x64 into a universal binary with re-signing and notarization
build-windows-appxbundle	Merges amd64 + arm64 AppX into a signed MSIX bundle
generate-update-yml	Generates electron-builder-compatible update metadata with SHA-512 checksums
publish-release	Creates/updates GitHub Releases and uploads all artifacts

Full 6-runner matrix build (Ubuntu amd64/arm64, Windows amd64/arm64, macOS arm64/Intel) out of the box.

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Quick Start

plugins {
    id("io.github.kdroidfilter.nucleus") version "<version>"
}

nucleus.application {
    mainClass = "com.example.MainKt"

    nativeDistributions {
        targetFormats(TargetFormat.Dmg, TargetFormat.Nsis, TargetFormat.Deb)
        packageName = "MyApp"
        packageVersion = "1.0.0"
    }
}

./gradlew run                              # Run locally
./gradlew packageDistributionForCurrentOS  # Build installer for your OS

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Runtime Libraries

Use them independently or together — each module is published to Maven Central.

Module	Artifact	Description
Core Runtime	nucleus.core-runtime	Platform detection, single instance, deep links, executable type detection
AOT Runtime	nucleus.aot-runtime	AOT cache mode detection (training / runtime / off)
Updater	nucleus.updater-runtime	Auto-update engine with GitHub/S3 providers, progress tracking, SHA-512 verification
Dark Mode Detector	nucleus.darkmode-detector	Reactive OS dark mode via JNI — macOS, Windows, Linux (D-Bus)
Decorated Window	nucleus.decorated-window	Custom title bar with native controls — design-system agnostic
Decorated Window Material	nucleus.decorated-window-material	Material 3 integration for decorated windows and dialogs
Linux HiDPI	nucleus.linux-hidpi	Native HiDPI scale factor detection on Linux (JNI)
GraalVM Runtime	nucleus.graalvm-runtime	Native-image bootstrap + font substitutions (includes linux-hidpi)

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Sponsor: Automatic GraalVM Reflection Plugin

Nucleus already supports GraalVM Native Image for instant startup and low memory usage — but configuring reflection metadata remains a major pain point.

I'm looking for sponsors to fund the development of an automatic reflection resolution plugin that would eliminate most of the manual configuration work. This would make native-image practical for large Compose Desktop applications while keeping full compatibility with the Java ecosystem.

If you or your company are interested, please reach out via GitHub Issues or GitHub Discussions. Read more about this in the GraalVM Native Image docs.

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Requirements

Requirement	Version	Note
JDK	17+ (25+ for AOT cache)	JBR recommended
Gradle	8.0+
Kotlin	2.0+

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Documentation

Full documentation is available at nucleus.kdroidfilter.com.

License

MIT — See LICENSE.