Make export maven/gradle create runnable uber-jars

[quintesse]

Right now the maven/gradle export create runnable JARs but without the dependencies.

We should also generate an additional runnable "uber/shadow" JAR containing all the dependencies to make it really easy to run the end result.

Ideally those dependencies would also be available separately in a folder in the build/target folder, so the user could also run java -cp 'target/libs/*' target/myapp-0.0.1-jar

[wfouche]

Adding the maven-shade-plugin to a Maven pom.xml file

<plugin>
	<groupId>org.apache.maven.plugins</groupId>
	<artifactId>maven-shade-plugin</artifactId>
	<version>3.6.0</version>
	<executions>
		<execution>
			<phase>package</phase>
			<goals>
				<goal>shade</goal>
			</goals>
		</execution>
	</executions>
</plugin>

and running mvn package creates a runnable uber jar in target/App-999-SNAPSHOT.jar which can be run as

$ java -jar target/App-999-SNAPSHOT.jar

[wfouche]

Gradle just need a few updates applied to the build.gradle file:

task createFatJar(type: Jar) {
    manifest {
        attributes 'Main-Class': '........'
    }
    archiveBaseName = 'App-999-SNAPSHOT'
    duplicatesStrategy = DuplicatesStrategy.EXCLUDE
    from { configurations.runtimeClasspath.collect { it.isDirectory() ? it : zipTree(it) } }
    with jar
}

and then run task

$ gradle createFatJar

The self-contained JAR is then run with command:

$ java -jar build/libs/App-999-SNAPSHOT.jar

[wfouche]

Gradle changes tested to work with Java, Groovy and Kotlin.

The Maven pom.xml change was only tested to work with Java; the Maven generated JARs for Groovy and Kotlin could not find the MainClass at runtime (might just be a config issue).

[maxandersen]

you do know there is this tool called jbang that can run those jars using maven GAV just fine ?

i'm not against having option of generating uber-jars but I think it would make perfect sense the generated pom.xml/build.gradle has a comment or something mentioning you can just run the jar as is using jbang :)

[quintesse]

you do know there is this tool called jbang that can run those jars using maven GAV just fine ?

Well no, you can't run a JAR that has dependencies, even with JBang :-)

The moment you export a script to Maven/Gradle and then build it we don't have any information about dependencies that JBang could use. (There's no extra information in the META-INF and no access to the source).

Also, for me the whole idea of a project export is because you want something that is independent from JBang. The uber jar is just a nice touch that gives you a user experience that's most similar to using JBang. Seems like a small thing to add for a big user benefit.