Add a JPMS module descriptor

[Benjamin Marwell]

I already tried to, but I cam back with a little more knowledge

Please add a Java 9+ JPMS module descriptor. PR will follow.

Technical details of the upcoming PR

1. Add a java9+ <profile><id>java9</id></profile>
2. In this profile, the folder src/main/java9 is added as an additional source folder
3. The source folder contains a module-info.java.

This will require a JDK9+ for compilation, but the whole rest of the source code will still produce java8 bytecode. I.e. no compatiblity issues.

The only file which will be compiled to Java9+ is the module descriptor. It will transparently be included in the resulting jar archive.

We do this in the maven-jlink-plugin the same way. A lot of plexus maven plugins do this as well.

Jlink example:

• 9+ Source code: https://github.com/apache/maven-jlink-plugin/tree/master/src/main/java9/org/apache/maven/plugins/jlink
• 9+ pom profile: https://github.com/apache/maven-jlink-plugin/blob/master/pom.xml#L201-L247

‌

Benefit / User stories

Applications requiring snakeyaml will be able to be packed into a jlink or jpackage archive, or even easier with the client-maven-plugin for gluon. At the moment this will not work, as at least jlink and jpackage require all dependencies to be modules.

[Andrey Somov]

Please be aware that SnakeYAML is under Java 7 (not Java 8)

I am afraid it will create compatibility issues.

Why not to migrate to Engine ? And implement this there ?

[Benjamin Marwell]

Hi Andrey, it does not really matter if it is Java 7 or 8. The only difference will be that there is a new META-INF/java9 directory in the jar file, containing a module-info.java.

What is “Engine”?

[Alexander Maslov]

I see you mention client-maven-plugin plugin. So, I expect you want to cross-platform application (like Android maybe).
But android version and non-android version would need to have different module-info.java files (e.g. android one does not require java.desktop).

I think making multirelease jar should not be a problem, since maven-compile-plugin supports it.

But I am not sure should we really do it in this project.
I guess it is also possible to use https://github.com/moditect/moditect to inject module-info.class for the dependencies missing it.

[Andrey Somov]

Engine - https://bitbucket.org/asomov/snakeyaml-engine (YAML 1.2 and Java8+)

[Benjamin Marwell]

I am not able to get the tests working I could upload a draft PR if you wish.

Btw: I do not think snakeyaml requires java.desktop at all.

[Andrey Somov]

./mvnw clean install
./docker-run-jdk7.sh

[Benjamin Marwell]

About snakeyaml-engine: Oh great! I didn’t know about that! I will now convert to snakeyaml-engine.

You are right that this issue will not make sense here. Thanks for the clarification!

[Benjamin Marwell]

Makes no sense here, users should update to snakeyaml-engine first.

[Andrey Somov]

SnakeYAML Engine has different API (no magic to support JavaBeans)

[Alexander Maslov]

@Benjamin Marwell snakeyaml uses Introspection which uses java.beans package which is part of java.desktop https://docs.oracle.com/javase/9/docs/api/java.desktop-summary.html