Add an automatic module name

[carlosame]

While I'm not an enthusiast of Java modularization, unfortunately Java libraries that aren't module-aware are increasingly being a source of compiler warnings as people migrate to newer JDKs.

It would help if dom4j set up an automatic module name in the Jar manifest, like:

Automatic-Module-Name: org.dom4j

I'm not familiar with gradle, but apparently the following would work:

jar {
  manifest {
    attributes('Automatic-Module-Name': 'org.dom4j')
  }
}

See https://guides.gradle.org/building-java-9-modules/#optional_add_code_automatic_module_name_code_manifest_entries_for_all_other_projects

Of course that a full module-info would also be a good thing, but the above solution is simple and solves the main issue of having to rely on generated module names.

[ColonelBlimp]

Can I up-vote this one 👍

[carlosame]

This issue was marked for 2.1.2, but 2.1.2/2.1.3 went out without it so I prepared a pull request. It is tested and gives the desired result.

[reinhapa]

@FilipJirsak as a OpenJDK contributor I can definitively support this PR as it should be good practice to supply at least the Automatic-Module-Name in not jet modular libraries in order to have a stable library identification as explained here