PARQUET-1925: Introduce Velocity Template Engine to Parquet Generator

[belugabehr]

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[belugabehr]

I like this very much. Would it be possible to have a test to check the output of the template?

Great! I started working on some of the more complex templates, but I didn't want to invest too much time before getting some buy-in on this effort.

I was manually generating and compiling the output for testing. I'll see if I can write a unit test.

[belugabehr]

OK. I added a unit test. I don't love the test, but it's something (and better than nothing). I'm also not sure how good of an example it will be for future tests in this 'generator' project.

I ran into a host of issues trying to test this. It's probably best to, in the future, change Version to implement an interface and then use normal getters instead of static fields. Since this class is compiled without any interface, there is nothing to import into the test at compile time in order to cast it to something I can then easily test against.

[belugabehr]

@Fokko @gszadovszky What are your thoughts on this and moving it forward?

[gszadovszky]

It looks good to me. We already have the unit test VersionTest to validate Version. Writing this additional test for the code generation made me more confident accepting this change. I am not an expert of velocity but looks much better than our original code so I would appreciate your work going forward.

[gszadovszky]

@belugabehr, are you planning to work further in this PR or shall I merge it as is?

[shangxinli]

@belugabehr As @gszadovszky asked, do you plan to work on this further?