[Java] Allocate the FieldReader for Arrow Vectors only on demand. Also introduce getTransferPair which takes Field as parameter.

[prashanthbdremio]

Describe the enhancement requested

[Java] Allocate the FieldReader for Arrow Vectors only on demand. Also introduce getTransferPair which takes Field as parameter.

1. FieldReader objects are created in the constructor of arrow vectors. FieldReader objects might not be needed in all cases. So create them only if required. https://github.com/apache/arrow/blob/master/java/vector/src/main/java/org/apache/arrow/vector/BitVector.java#L83

2. Introduce a new getTransferPair method which takes 'Field' as a parameter. In some cases its useful to pass a 'Field' object directly and not create a new 'Field' everytime. https://github.com/apache/arrow/blob/master/java/vector/src/main/java/org/apache/arrow/vector/BitVector.java#L553

Component(s)

Java

[rtadepalli]

take

[lwhite1]

Other than my comment about trying to lift the code for a thread-safe supplier from Guava, this looks good to me. FWIW, we did something similar with org.apache.arrow.util.Preconditions in the memory component.