The java sessionDataset's functions is somehow redundant

Given a column index, the data type is unique, so we should provide users with a single "Get" api instead of apis with type. Besides, getting timestamp can be done without making sure what the column is, and the current logic is false when users gives column names or indexes other than "Time" or 1

Start by locating the Java sessionDataset implementation and its typed Get APIs. Compare timestamp retrieval for column names and indexes other than “Time” or 1; done means the redundant typed APIs are consolidated and timestamp lookup works for valid column identifiers without the current assumption.

Written by the indexing model from the issue text.