Hibernate retrieve timestamps in UTC

I am using hibernate + spring and want to store/load timestamps in UTC. I've read that I should add a property, so I added this to my application.properties

spring.jpa.properties[hibernate.jdbc.time_zone]=UTC

This worked for one part of the problem - now dates are saved in utc in the database. But when I retrieve timestamps, they are transformed into default timezone. How can I fix this without setting default time zone to UTC? The property of the entity has type LocalDateTime. I ran the code, and noticed that the proper result set method is used during get(the one that accepts calendar) with instance that has zone info storing UTC. But after setting calendar's values to the one retrieved from the database, the calendar is transformed into Timestamp with this code

Timestamp ts = new Timestamp(c.getTimeInMillis());

In debug mode, I see that ts stores cdate field with value of timestamp in default time zone(not UTC).

First of all, if we are talking about Hibernate 5 (5.2.3 - 5.6.x if to be precise) the purpose of hibernate.jdbc.time_zone setting is not to give the ability for application developer to implement some kind of sophisticated date/time logic, but to synchronize persistence provider with underlying database, that is clearly stated in the corresponding CR:

Currently my database has implicit date times in UTC. No zoned data is appended to the end of the string (e.g. "2013-10-14 04:00:00"). When Hibernate reads this as a ZonedDateTime, it incorrectly reads it in as EST, as that is the TimeZone of the JVM. It would be nice to be able to specify the TimeZone of a field by an annotation perhaps.

basically: you definitely need to set up hibernate.jdbc.time_zone if (mine: and only if) SQL statement like SELECT SYSDATE FROM DUAL (SELECT LOCALTIMESTAMP for PostgreSQL, etc) returns something, what you do not expect, in that case Hibernate will start adjusting non-timezone-aware JDBC data to something more or less reliable for application - that is exactly what you are observing (when I retrieve timestamps, they are transformed into default timezone)

At second, any speculations around JSR-310 and JDBC 4.2 (like for timezone-aware java types you need to define DB columns as timestamp with time zone), are not correct in case of Hibernate 5, that is mentioned in the corresponding CR as well:

The whole idea of "stored TZ" really depends on how the database/driver treats TIMESTAMP and whether it supports a "TIMESTAMP_WITH_TIMEZONE" type. I personally think it is a huge mistake to save the specific TZ differences to the DB, so I would personally continue to not support TIMESTAMP_WITH_TIMEZONE types. This would mean we never have to bind the Calendar because we could simply convert the value to to the JVM/JDBC TZ ourselves. Specifically I would suggest that we (continue to) assume that the driver has been set up such that the same TZ is used when ...

And indeed, if you try to find usage of java.sql.Types#TIMESTAMP_WITH_TIMEZONE in Hibernate 5 sources you will find nothing, just because that time Hibernate developers didn't get a common opinion about how timezone conversions should work in cases of different Java versions, Java types, DB engines and JDBC drivers (they are developing the most popular (mine: the only one) JPA implementation, that is definitely not the same as develop microservice), however, there are a lot of related changes in Hibernate 6 (check TimeZoneStorageType for example). In Hibernate 5 all timezone conversion logic passes through TimestampTypeDescriptor:

@Override
protected X doExtract(ResultSet rs, String name, WrapperOptions options) throws SQLException {
  return options.getJdbcTimeZone() != null ?
   javaTypeDescriptor.wrap( rs.getTimestamp( name, Calendar.getInstance( options.getJdbcTimeZone() ) ), options ) :
   javaTypeDescriptor.wrap( rs.getTimestamp( name ), options );
}

and as you can see, Hibernate 5 just gives a hint to JDBC driver, how the last should process #getTimestamp call:

Retrieves the value of a JDBC TIMESTAMP parameter as a java.sql.Timestamp object, using the given Calendar object to construct the Timestamp object. With a Calendar object, the driver can calculate the timestamp taking into account a custom timezone and locale. If no Calendar object is specified, the driver uses the default timezone and locale.

in regard to your case:

you either need to use timezone-aware java types (ZonedDateTime/OffsetDateTime, or even Instant) or code your own Hibernate type, which will handle timezone conversions - that is not so hard as it might seem.