How to get UTC timestamps from JDBC+postgreSql timestamp?

Question

I created a table like like this in PostgreSQL:

create table myTable (
    dateAdded timestamp(0) without time zone null          


        

Answer 1

Solution

Set UTC as default timezone of your JVM -Duser.timezone=UTC or set your whole OS to UTC.

Background

In Postgres both TIMESTAMP and TIMESTAMP WITH TIMEZONE are stored the same way - number of seconds since Postgres epoch (2000-01-01). The main difference is what Postgres do when it saves timestamp value such as 2004-10-19 10:23:54+02:

• without TZ the +02 is just stripped away
• with TZ a -02 correction is performed to make it UTC

Now the interesting thing is when JDBC driver loads the value:

• without TZ the stored value is shifted by the user's (JVM / OS) TZ
• with TZ the value is considered to be UTC

In both cases you will end up with java.sql.Timestamp object with user's default TZ.

Time Zones

Timestamps without TZ are pretty limited. If you have two systems connected to your database, both with different TZ, they will interpret timestamps differently. Therefore, I strongly advice you to use TIMESTAMP WITH TIMEZONE.

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Update

You can tell JDBC what kind of TZ it should use when reading timestamp via ResultSet#getTimestamp(String, Calendar). Excerpt from JavaDoc:

This method uses the given calendar to construct an appropriate millisecond value for the timestamp if the underlying database does not store timezone information.