How to read timezone from 'timestamp with time zone' column?

Question

I am unable to find a way to read timezone value in PostgreSQL column of type timestamp with time zone.

JDBC offers method java.sql.ResultSet#getTimestamp(int, java.util.Calendar) but I must provide my own calendar. I have see no way to obtain that calendar from timestamp field I am reading.

I am working on system that stores time data of multiple timezones. I need to save data with timezone information, and be able to read that timezone back from database.

Is it possible without hacks like

• storing timezone value in another field
• storing date as string, like 'Wed 17 Dec 07:37:16 1997 PST'

I am using JDBC 41 (JDBC4 Postgresql Driver, Version 9.4-1201), java 8.

Answer 1

The PostgreSQL documentation here says that:

For timestamp with time zone, the internally stored value is always in UTC (Universal Coordinated Time, traditionally known as Greenwich Mean Time, GMT).

So there is no need to "store the time zone [that corresponds to the timestamp value]" per se; the timestamp with time zone values are always stored as UTC.

Also, there is no need to "obtain the Calendar from the timestamp field". The purpose of the Calendar is for you to define the particular timezone that you want to work with in your Java application.

In other words, timestamp with timezone does not store values from various timezones (e.g., some in EST, others in PST, etc.), it converts everything to UTC when the timestamp values are inserted.