build.gradle

// apply java plugin since we develop a java app
apply plugin: 'java'

// specify source compatibility & encoding
sourceCompatibility = 1.9
compileJava.options.encoding = 'UTF-8'

// we use the gradle wrapper in version 4.3
task wrapper(type: Wrapper) {
    gradleVersion = '4.5.1'
    distributionUrl = "https://services.gradle.org/distributions/gradle-$gradleVersion-all.zip"
}

// repositories used for dependency lookup
repositories {
    mavenCentral()
    jcenter()
}

// dependencies (compile-time, runtime & testing)
dependencies {
    // add your dependencies here
}

def jdk = System.getProperty("java.home")
def moduleName = "eu.mihosoft.tutorials.nativejdk9apptemplate"
def mainClass = 'eu.mihosoft.tutorials.nativejdk9apptemplate.Main'


// jar file task (we add the main class and classpath attributes to the manifest)
jar {
    manifest {
        attributes(
                'Main-Class': mainClass,
        )
    }
}

// creates application bundle (executable + runtime)
task javaPackager(type: Exec, dependsOn: assemble) {

    workingDir project.projectDir
    commandLine = [
            'javapackager',
            '-deploy',
            '-nosign',
            '-native', 'image',
            '-outdir', "${buildDir}/distribution",
            '-outfile', project.name,
            '-name', project.name,
            '-appclass', mainClass,
            '-p', "${jdk}/jmods${File.pathSeparator}${buildDir}/libs",
            '--add-modules', moduleName,
            '-m', "$moduleName/$mainClass"
    ]
}

// removes bloated runtime created by javapackager
task cleanPackagerRuntime(dependsOn: javaPackager) {
    doLast() {
        File runtimeFile = new File("${buildDir}/distribution/${project.name}/runtime")
        runtimeFile.deleteDir()
        System.out.println("deleting bloated runtime in " + runtimeFile)
    }
}

// creates a replacement runtime via jlink command (much smaller than jpackager)
task createFinalAppBundle(type: Exec, dependsOn: [cleanPackagerRuntime]) {

    workingDir project.projectDir
    commandLine = [
            'jlink',
            '-p', "${jdk}/jmods${File.pathSeparator}${buildDir}/libs",
            '--add-modules', moduleName,
            '--strip-debug',
            '--no-header-files',
            '--no-man-pages',
            '--strip-native-commands',
            "--vm=server",
            "--compress=2",
            '--output', "${buildDir}/distribution/${project.name}/runtime"
    ]

    doLast{
        System.out.println("Application '${project.name}' packaged.")
        System.out.println(" -> location: ${buildDir}/distribution/${project.name}/")
    }
}