Remove unused GPL-licensed code

[bencomp]

For unknown reasons, in 2009 several files from the JDK were copied into the Dataverse codebase, instead of referenced.
It appears that these classes weren't really used.

What this PR does / why we need it:

It removes clear examples of license confusion (if not copyright infringement) caused by including GPL-licensed code in a Apache 2.0 codebase with Harvard copyright notice. I am not a lawyer, however, and wouldn't want to get involved in legal troubles.

Which issue(s) this PR closes:

Partially addresses #2576 – which had been closed "while waiting for legal advice".

Special notes for your reviewer:

If you ever want to use services and service providers, you could do it the Java way, explained at https://docs.oracle.com/en/java/javase/11/docs/api/java.base/java/util/ServiceLoader.html.

It appears that @landreev wanted to use the ServiceRegistry at some point in TabularDataFileReader.getTabDataReaderByMimeType(String mimeType).

I'd appreciate a positive review to have this PR count towards my Hacktoberfest goal.

Suggestions on how to test this:

See that there are no compilation errors and test failures without these classes. Check that there are no more references to these classes in comments.

Does this PR introduce a user interface change? If mockups are available, please link/include them here:

Is there a release notes update needed for this change?:

Additional documentation:

[bencomp]

I just noticed that the ServiceLoader pattern is in use for Exporters, so it's not completely new. :)

[coveralls]

Coverage increased (+0.07%) to 20.051% when pulling ddfae97 on bencomp:remove-gpl-code into 470f99b on IQSS:develop.

[qqmyers]

It does indeed look like unused code (and build/test passes). FWIW, it does not look like there is any copyright/license issue - the Classpath Exception on these classes is meant to allow them to be used in other software (on a different classpath) without the GPL applying.

[bencomp]

Thanks for the review, @qqmyers ! I wasn't aware of the Classpath Exception.
So even if copyright may not have been an issue, removing these unused classes may allow more attention to go to actually used classes.

[bencomp]

Is there anything that I can do to get this merged? The checks passed and there was a positive review over 9 months ago… Of course I don't want to sound impatient 😉

[landreev]

Hello,
I personally simply missed this PR last fall. And it looks like nobody ever put it into our workflow queue, and that was the only reason it sat all this time. (Not because anybody thought there was a problem with the PR).
We are not merging new PRs right now, because we are in the process of putting together a platform upgrade-focused release. But once it is out (shortly), we'll make sure to add this PR to the queue.
I did add the code in question to the Dataverse source tree, but I merely copy-and-pasted it from a project that preceded Dataverse where it was written by another developer. It was originally there to be able to load ingest plugins from external jars. But since we stopped doing that it is indeed unused as of now.

[cmbz]

Added to 6.1 milestone as per 2023/08/24 discussion.

[pdurbin]

API tests are passing: https://jenkins.dataverse.org/job/IQSS-Dataverse-Develop-PR/job/PR-9009/2/testReport/

[scolapasta]

@bencomp now that we've released 6.0, I'm moving waiting 6.1 issues back to the board.

But could you first handle the 6.0 merge and address any EE10 issues. Thanks.

[bencomp]

Although the Jenkins build failed for unknown reason, I think this is ready, @scolapasta. As far as I can tell, there are no EE10 issues.

[landreev]

Yes, Jenkins appears to be failing for unrelated reasons (PostgreSQL config).

Although the Jenkins build failed for unknown reason, I think this is ready, @scolapasta. As far as I can tell, there are no EE10 issues.