When Hibernate writes a Java Calendar object to an SQL TIMESTAMP column, to which time zone does it adjust the date, that of the computer or that specified in the calendar object (or some other)?
When Hibernate reads the TIMESTAMP into the calendar object, to which time zone does it translate the date?
When Hibernate writes a Java Calendar object to an SQL TIMESTAMP column, to which time zone does it adjust the date, that of the computer or that specified in the calendar object (or some other)?
Hiberante 3.x uses the following in the CalendarType (see HB-1006):
public void set(PreparedStatement st, Object value, int index) throws HibernateException, SQLException {
final Calendar cal = (Calendar) value;
//st.setTimestamp( index, new Timestamp( cal.getTimeInMillis() ), cal ); //JDK 1.5 only
st.setTimestamp( index, new Timestamp( cal.getTime().getTime() ), cal );
}
So Hibernate uses PreparedStatement#setTimestamp(int, Timestamp, Calendar) which uses the time zone of the calendar.
When Hibernate reads the TIMESTAMP into the calendar object, to which time zone does it translate the date?
Well, again, let's look at the CalendarType class:
public Object get(ResultSet rs, String name) throws HibernateException, SQLException {
Timestamp ts = rs.getTimestamp(name);
if (ts!=null) {
Calendar cal = new GregorianCalendar();
if ( Environment.jvmHasTimestampBug() ) {
cal.setTime( new Date( ts.getTime() + ts.getNanos() / 1000000 ) );
}
else {
cal.setTime(ts);
}
return cal;
}
else {
return null;
}
}
So Hibernate constructs a default GregorianCalendar using the current time in the default time zone with the default locale.
As a side note, I highly suggest to read the following question:
I just spent 6 hours on a similar issue and thought I would document it here. Hibernate indeed does use the JVM timezone but it can be changed by extending the CalendarType like this:
public class UTCCalendarType extends CalendarType {
private static final TimeZone UTC = TimeZone.getTimeZone("UTC");
/**
* This is the original code from the class, with two changes. First we pull
* it out of the result set with an example Calendar. Second, we set the new
* calendar up in UTC.
*/
@Override
public Object get(ResultSet rs, String name) throws SQLException {
Timestamp ts = rs.getTimestamp(name, new GregorianCalendar(UTC));
if (ts != null) {
Calendar cal = new GregorianCalendar(UTC);
cal.setTime(ts);
return cal;
} else {
return null;
}
}
@Override
public void set(PreparedStatement st, Object value, int index) throws SQLException {
final Calendar cal = (Calendar) value;
cal.setTimeZone(UTC);
st.setTimestamp(index, new Timestamp(cal.getTime().getTime()), cal);
}
}
the secret sauce here is :
rs.getTimestamp(name, new GregorianCalendar(UTC));
This converts the timezone from the result set to whatever timezone you want. So what I did was use this type with any UTC calendars and the standard Hibernate type for the local time. Works slick as a whistle...
By default, it's up to the JDBC Driver to decide what timezone to use. Typically, the JVM time zone is used unless you configure the JDBC Driver to use a custom time zone.
If you want to control what time zone is used, you can set the time zone at the JVM level. If you want the JVM time zone to differ from the one used by the database, then you need to use the hibernate.jdbc.time_zone Hibernate 5.2 configuration property:
<property name="hibernate.jdbc.time_zone" value="US/Eastern"/>
If you don't want to write the code yourself, you can just use the open source library DbAssist. After applying this fix, the dates in the database will be treated by JDBC and then Hibernate as UTC, so you do not even have to change your entitiy classes.
For example, if you are using JPA Annotations with Hibernate 4.3.11, add the following Maven dependency:
<dependency>
<groupId>com.montrosesoftware</groupId>
<artifactId>DbAssist-4.3.11</artifactId>
<version>1.0-RELEASE</version>
</dependency>
Then you just apply the fix:
For Hibernate + Spring Boot setup, add the @EnableAutoConfiguration annotation before the application class.
For HBM files, you have to change the entity mapping files to map Date types to the custom one:
<property name="createdAt" type="com.montrosesoftware.dbassist.types.UtcDateType" column="created_at"/>
If you want to learn more about how to apply the fix for different Hibernate versions (or HBM files), refer to the project's github. You can also read more about the time zone shift issue in this article.
