Add maven wrapper to scala project.

[frankfliu]

Add maven wrapper to scala project, this removed maven dependency from host machine.
And this will also eliminate build script compatibility issue with different maven version.

Checklist

Essentials

Please feel free to remove inapplicable items for your PR.

• Changes are complete (i.e. I finished coding on this PR)
• All changes have test coverage:
• Unit tests are added for small changes to verify correctness (e.g. adding a new operator)
• Nightly tests are added for complicated/long-running ones (e.g. changing distributed kvstore)
• Build tests will be added for build configuration changes (e.g. adding a new build option with NCCL)
• Code is well-documented:
• For user-facing API changes, API doc string has been updated.
• For new C++ functions in header files, their functionalities and arguments are documented.
• For new examples, README.md is added to explain the what the example does, the source of the dataset, expected performance on test set and reference to the original paper if applicable
• Check the API doc at http:https://mxnet-ci-doc.s3-accelerate.dualstack.amazonaws.com/PR-$PR_ID/$BUILD_ID/index.html
• To the my best knowledge, examples are either not affected by this change, or have been fixed to be compatible with this change

[marcoabreu]

As per previous discussion (sorry on mobile, don't have link on hand), we are not allowed to published binaries (the jar file). Basically Apache forbids that action for all of it's projects

[lebeg]

As per previous discussion...

@marcoabreu Please provide the link.

I would consider reading answers in LEGAL-427 carefully as well.

[marcoabreu]

I don't understand how that link is relevant. The Apache release guidelines forbid binaries in source releases

[Roshrini]

@nswamy Can you please take a look?
@mxnet-label-bot Add [pr-awaiting-review, Scala]

[sandeep-krishnamurthy]

@frankfliu you have any comments on the concerns from @marcoabreu ?

[frankfliu]

@marcoabreu
checkin maven wrapper or gradle wrapper is very common practice in most of modern java projects.
check in binary files are bad in general, which is not able diff while updating, and will increase git repo size rapidly. But It should be OK for tools since they are not part of source code and won't be updated frequently. And maven wrapper and gradle wrapper jar files are tiny.

You can find many apache project with maven wrapper checked in github:
Here is a link to apache log4j project: https://github.com/apache/logging-log4j2/tree/master/.mvn/wrapper

[anirudhacharya]

@marcoabreu ping for a relook at this PR.

[lanking520]

Please add some retries in here to reduce the failure

[piyushghai]

I don't think it is needed. It's code coming in from Maven Wrapper package.

[lanking520]

@frankfliu Please raise a discussion on dev@ to discuss about uploading the binary

[marcoabreu]

Thanks @lanking520 , that's a great idea. We have been advised by out mentors in the past to specifically remove the maven wrapper binary, but it might be good to bring it up again.

[mjwall]

Marco, Agree you shouldn't check in binaries, but you can exclude the maven wrapper binary from source control and it will be downloaded when needed. See https://github.com/takari/maven-wrapper#usage-without-binary-jar. Interested to read any links referencing those discussions if you have them. Mike

…

On Thu, Jan 24, 2019 at 2:56 PM Marco de Abreu ***@***.***> wrote: Thanks @lanking520 <https://github.com/lanking520> , that's a great idea. We have been advised by out mentors in the past to specifically remove the maven wrapper binary, but it might be good to bring it up again. — You are receiving this because you are subscribed to this thread. Reply to this email directly, view it on GitHub <#13702 (comment)>, or mute the thread <https://github.com/notifications/unsubscribe-auth/AAAJJsRHzUCRGh1cKWTB98CTVQN9lbhNks5vGg_bgaJpZM4Zcl_I> .

[marcoabreu]

Ah, that's an excellent alternative then :)

There you go: https://lists.apache.org/thread.html/d409819b554745937103b60d36ad3f5b2b1300fe8ae826fb0e665f7f@%3Cdev.mxnet.apache.org%3E

[marcoabreu]

Original source: https://lists.apache.org/thread.html/2bf07a377cac35d4940f0fbf7f647f46a38d2845e5dbb3c650f367d7@%3Cgeneral.incubator.apache.org%3E

[marcoabreu]

Open LEGAL ticket: https://issues.apache.org/jira/browse/LEGAL-288

[mjwall]

Great, thanks for the links. I don't see the issue if the jar file is not included in the source and not included in the distirbution, but interested to hear other's interpretations. LEGAL-288 to me is about including that jar file. Was this asked on the dev list?

…

On Thu, Jan 24, 2019 at 8:46 PM Marco de Abreu ***@***.***> wrote: Open LEGAL ticket: https://issues.apache.org/jira/browse/LEGAL-288 — You are receiving this because you commented. Reply to this email directly, view it on GitHub <#13702 (comment)>, or mute the thread <https://github.com/notifications/unsubscribe-auth/AAAJJuTxoSHcdzsyqmTKqghtgt-Yhbymks5vGmICgaJpZM4Zcl_I> .

[marcoabreu]

We had it in the past and were asked to remove it by mentors. I've linked both threads

If there is an alternative to a binary file - which is the case according to your link - I'm also in favour to not have them checked in at all as otherwise users will have to manually download them and we have to manually remove them.

[frankfliu]

@marcoabreu I removed jar file. The maven wrapper can compile MavenWrapperDownloader.java and download the .jar file on the fly.

[marcoabreu]

Awesome, thank you! :)

[lanking520]

@frankfliu Since we are good with this PR, please add the final changes on the

• Jenkins file
• Publish Jenkinsfile
• Makefile
• Docs on website

In order to coordinate this change. Thanks

[vandanavk]

@mxnet-label-bot update [Scala, pr-awaiting-merge]

[lanking520]

@frankfliu please add the remaining items in JIRA as a backlog item