[Java] Getting length of data buffer and base variable width vector

[asfimport]

For string data buffer and base variable width vector can we have a way to get length of the data? 

For instance, in ArrowColumnVector in StringAccessor we use stringResult.start and stringResult.end, instead we would like to get length of the data through an exposed function.

Reporter: Gaurangi Saxena
Assignee: Ji Liu / @tianchen92

PRs and other links:

• GitHub Pull Request #6684
• GitHub Pull Request #7280

_{Note: This issue was originally created as ARROW-8158. Please see the migration documentation for further details.}

[asfimport]

Ji Liu / @tianchen92:
Hi, I think one could get valid data length by BaseVariableWidthVector#sizeOfValueBuffer.

https://github.com/apache/arrow/blob/master/java/vector/src/main/java/org/apache/arrow/vector/BaseVariableWidthVector.java#L582

[asfimport]

Micah Kornfield / @emkornfield:
@tianchen92  The issue is there isn't a clear way to get the length of an individual VarChar or Bytes element (one needs to go through the holder or access the offsets buffer directly).  A similar issue exists for lists.

[asfimport]

Ji Liu / @tianchen92:
@emkornfield  I see, I could add a method like getDataLength(int index) for variable width vector.

For lists, we already have getElementStartIndex/getElementEndIndex, is it enough or still need to add a method like getElementLength?

[asfimport]

Micah Kornfield / @emkornfield:
we should probably be consistent and have getEndIndex or something like that instead of length.

[asfimport]

Micah Kornfield / @emkornfield:
Issue resolved by pull request 6684
#6684