[FSTORE-1008] enable interacting with java client to hopsworks

[davitbzh]

This PR adds/fixes/changes...

• please summarize your changes to the code
• and make sure to include all changes to user-facing APIs

JIRA Issue: -

Priority for Review: -

Related PRs: -

How Has This Been Tested?

• Unit Tests
• Integration Tests
• Manual Tests on VM

Checklist For The Assigned Reviewer:

- [ ] Checked if merge conflicts with master exist
- [ ] Checked if stylechecks for Java and Python pass
- [ ] Checked if all docstrings were added and/or updated appropriately
- [ ] Ran spellcheck on docstring
- [ ] Checked if guides & concepts need to be updated
- [ ] Checked if naming conventions for parameters and variables were followed
- [ ] Checked if private methods are properly declared and used
- [ ] Checked if hard-to-understand areas of code are commented
- [ ] Checked if tests are effective
- [ ] Built and deployed changes on dev VM and tested manually
- [x] (Checked if all type annotations were added and/or updated appropriately)

[kennethmhc]

why change it to StreamFeatureGroup?

[davitbzh]

FeatureGroupBaseForApi was used as a dummy class for API calls. In hsfs only abstract classes were present and it is not initializable. Since we added now support for StreamFeatureGroup, it can do the job

[kennethmhc]

General question: what methods should be included in the java client?

[davitbzh]

Only thing in java client can be done is fetch FG, FV metadata and get feature vectors. I don't see any other use cases

[kennethmhc]

why removing all the abstract method? Are they not needed for spark/flink etc? same for featurestorebase and featuregroupbase.
I think you can implement the abstract method as "not available" in the FeatureView

[davitbzh]

My point was that who will use addTag from Flink or Beam? It doesn't make sense. But it is possible do add since only api classes are used

[kennethmhc]

When I was testing it, I found a bug. Can you change line 215 in VectorServer to

      String zippedTupleString =
          zipArraysToTupleString(preparedStatementParameters.get(fgId)
                  .entrySet()
                  .stream()
                  .sorted(Comparator.comparingInt(Map.Entry::getValue))
                  .map(e -> entry.get(e.getKey()))
              .collect(Collectors.toList()));

Basically, the problem is that when there are multiple primary key, they need to be sorted according to the index of preparedStatementParameters