Application with JNI Library

You can open this sample inside an IDE using the IntelliJ native importer or Eclipse Buildship.

This sample shows how a JVM application in Gradle can use a JNI library. The library has no dependencies, and the build has a minimal configuration.

In this sample, we are using a JNI library implemented in Java and C++ within an application implemented in Java; however, this applies to other JVM and native languages as well.

GroovyKotlin

build.gradle

plugins {
	id 'java'
	id 'application'
}

import org.gradle.util.GradleVersion

application {
	if (GradleVersion.current() >= GradleVersion.version('6.7')) {
		mainClass = 'com.example.app.Main'
	} else {
		mainClassName = 'com.example.app.Main'
	}
}

dependencies {
	implementation project(':jni-library')
}

build.gradle.kts

plugins {
	id("java")
	id("application")
}

import org.gradle.util.GradleVersion
import org.gradle.api.plugins.JavaApplication

// Create a shim method to support newer Gradle version
fun JavaApplication.setMainClass(className: String) {
	if (GradleVersion.current() >= GradleVersion.version("6.7")) {
		val getMainClass = javaClass.getMethod("getMainClass")
		val mainClass = getMainClass.invoke(this) as Property<String>
		mainClass.set("com.example.app.Main")
	} else {
		mainClassName = "com.example.app.Main"
	}
}

application {
	setMainClass("com.example.app.Main")
}

dependencies {
	implementation(project(":jni-library"))
}

To build the library:

$ ./gradlew run

> Task :run
Bonjour, World!

BUILD SUCCESSFUL
6 actionable tasks: 6 executed

It’s also possible to build a distribution archive:

$ ./gradlew :distZip

BUILD SUCCESSFUL
8 actionable tasks: 3 executed, 5 up-to-date
$ ls ./build/distributions/*.zip
./build/distributions/jvm-application-with-jni-library.zip

It is possible to use the distribution on a system where the code wasn’t built, given the native component of the JNI library is supported on the platform:

$ mv ./build/distributions/jvm-application-with-jni-library.zip .
$ ./gradlew clean

BUILD SUCCESSFUL
2 actionable tasks: 2 executed
$ unzip jvm-application-with-jni-library.zip -d .
Archive:  /Users/daniel/jvm-application-with-jni-library.zip
   creating: /Users/daniel/jvm-application-with-jni-library/
   creating: /Users/daniel/jvm-application-with-jni-library/lib/
  inflating: /Users/daniel/jvm-application-with-jni-library/lib/jvm-application-with-jni-library.jar
  inflating: /Users/daniel/jvm-application-with-jni-library/lib/jni-library.jar
   creating: /Users/daniel/jvm-application-with-jni-library/bin/
  inflating: /Users/daniel/jvm-application-with-jni-library/bin/jvm-application-with-jni-library
  inflating: /Users/daniel/jvm-application-with-jni-library/bin/jvm-application-with-jni-library.bat
$ ./jvm-application-with-jni-library/bin/jvm-application-with-jni-library
Bonjour, World!

For more information, see JNI Library Plugin, C++ Language Plugin and Application Plugin reference chapters.