How one would access to internal representation of DataTypes.DateType from Spark (2.0.1) Java API?
From https://github.com/apache/spark/blob/51b1c1551d3a7147403b9e821fcc7c8f57b4824c/sql/catalyst/src/main/scala/org/apache/spark/sql/types/DateType.scala : "Internally, this is represented as the number of days from 1970-01-01."
