how to use utc in postgres timestamp with jdbc PrepareStatement parameter? - postgresql

Question

I'am using timestamp data type on pg9.4, but there come very strange problem with to_json.
now i am in Shanghai, UTC+08:00 timezone.
see below:
conn.createStatement().execute("set time zone 'UTC'");
String sql = "select to_json(?::timestamp) as a, to_json(current_timestamp::timestamp) as b";
PreparedStatement ps = conn.prepareStatement(sql);
Timestamp timestamp = new Timestamp(new Date().getTime());
ps.setTimestamp(1, timestamp);
ResultSet rs = ps.executeQuery();
while(rs.next()){
System.out.println("a " + rs.getString("a") + ", b " + rs.getString("b"));
}
output:
a "2015-09-24T16:52:42.529", b "2015-09-24T08:53:25.468191"
it's mean when i pass a TIMESTAMP parameter to pg with jdbc, the timezone is still in shanghai, not UTC.
this problem is not due to to_json function, i have make a table with one timestamp column, this problem still exits, the code of above is shortest sample.
how to let's all timestamp work in UTC timezone?

Answer 1

You need to set Calendar tzCal = Calendar.getInstance(TimeZone.getTimeZone("UTC"));, Before you create your prepared statement.
UPDATED CODE SNIPPET
conn.createStatement().execute("set time zone 'UTC'");
String sql = "select to_json(?::timestamp) as a, to_json(current_timestamp::timestamp) as b";
Calendar tzCal = Calendar.getInstance(TimeZone.getTimeZone("UTC"));
PreparedStatement ps = conn.prepareStatement(sql);
Timestamp timestamp = new Timestamp(new Date().getTime());
ps.setTimestamp(1, timestamp);
ResultSet rs = ps.executeQuery();
while(rs.next()){
System.out.println("a " + rs.getString("a") + ", b " + rs.getString("b"));
}
This way you will be able to set timezone to UTC in your JDBC call.
If you want to run the whole application/JVM in UTC, set -Duser.timezone=UTC flag while starting JVM.
HTH.