Add implementation of POI example

[kiryldz]

@yuryybk BTW wouldn't you like to squash commits a bit before future final merge?

[yuryybk]

@yuryybk BTW wouldn't you like to squash commits a bit before future final merge?

I prefer to squash commits after implementing feature where every commit is just a partial work to fix changes for feature and doesn't make sense independently for others.

Here every commit is directly related to notes of the review, so changes could be easily checked. In my previous teams we even forced to not merge PR review changes together.

But I understand that it is mostly depends on the team and if you prefer squashes or less commits in history for some reasons - let's follow this ideas

@kiryldz

[yuryybk]

PTAL on Java implementation

[yuryybk]

@yunikkk @alexander-kulikovskii PTAL on Java implementation