Build as multi release jar

[Til7701]

As mentioned in #61 here is the build config to build this as a multi release jar with a module-info.java for Java 9+. This allows using this dependency with JLink while maintaining support for Java 8.

• update GitHub Action to use JDK 11
• added module info in java9 source folder
• added executions for java 8 and 9
• removed automatic module
• added multi release entry to manifest

[wing328]

Sorry for late reply.

We're looking for maintainers: #71

Let me know if you're interesting in maintaining this project. Thank you.

[nrayburn-tech]

Instead of source/target, use release with 8.

[Til7701]

Its practically identical, but you are right. It's a bit clearer that way.

[nrayburn-tech]

I think release is meant to be a bit more robust in terms of ensuring backwards compatibility. I can’t say I actually know the difference other than release is typically used in newer Java versions.

[nrayburn-tech]

Does this work correctly in projects that only have the javax OR jakarta dependency? This project has both as a provided scope, so I expect tests/compile will pass. However an application/library that depends on this project will typically only have one or the other.

Sorry, I'm not super familiar with the module system.

[Til7701]

I have used this in one project when I first created the PR. That project is now suspended, but it worked with JLink at the time. I only hat the Jakarta namespace in that project.

[Til7701]

There is a problem with the javadoc plugin. Ill have to take a look at that later.

[Til7701]

The JavaDoc problem seems to be fixed now. I still don't really know what the problem was...

[nrayburn-tech]

There's the below warning emitted when building locally. I don't really understand anything about it, except that it can't be fixed without using Java 17 for the build step. It might be worth checking what other Jackson modules are doing today with Jackson v2 support.

[INFO] --- bundle:5.1.9:manifest (bundle-manifest) @ jackson-databind-nullable ---
[INFO] No MANIFEST.MF file found, generating manifest.
[WARNING] Manifest org.openapitools:jackson-databind-nullable:jar:0.2.8-SNAPSHOT : Classes found in the wrong directory: {META-INF/versions/9/module-info.class=module-info}
Manifest org.openapitools:jackson-databind-nullable:jar:0.2.8-SNAPSHOT : Classes found in the wrong directory: {META-INF/versions/9/module-info.class=module-info}

bndtools/bnd#3514 contains some suggestions on how to just ignore the message.
The real fix is to use a newer maven-bundle-plugin version that supports the multi-release jars. The maven-bundle-plugin is currently inherited from the parent pom, but could be overridden in this project directly.

I think it can be left alone, but it might be better to add the ignore message config with a note about fixing it when migrating to Java 17/Jackson 3.

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Aside from that, if the build passes after the merge conflicts are resolved I'm good with this.