Reading and Writing UTC Timestamps to DB with Hibernate

Problem

Reading and writing UTC timestamps to a database when the default timezone may change. E.g., this might happen in an application server if an application running in the same JRE changes the default timezone as follows:

    TimeZone.setDefault(TimeZone.getTimeZone("Europe/Zurich")); 

This is not possible as the applications are running in separated classloaders, you may say. I thought the same. And perhaps this must not happen because there is a spec that does forbid this (by the way, is there any?). However, it is possible to change the default timezone for all applications in the same node that way at least in Oracle Weblogic server. Try it out, if you dont't believe me.

Solution

The easiest solution to solve this problem I know is to create an own mapping type extending the standard Hibernate timestamp type org.hibernate.type.TimestampType:

package ch.meteoswiss.commons.hibernate;

import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Timestamp;
import java.util.Calendar;
import java.util.SimpleTimeZone;


/**
 * timestamp: A type that maps an SQL TIMESTAMP to a Java
 * java.util.Date or java.sql.Timestamp using UTC time zone.
 * @author Peter Keller
 */
public class UTCTimestampType extends org.hibernate.type.TimestampType {

    @Override
    public Object get(ResultSet rs, String name) throws SQLException {
        return rs.getTimestamp(name, createUTCCalendar());
    }

    /**
     * Creates UTC calendar. DO NOT USE a static calendar instance.
     * This may lead to concurrency problems with (at least) the Oracle DB
     * driver!
     * @return Calendar with UTC time zone.
     */
    private static Calendar createUTCCalendar() {
        final Calendar c = Calendar.getInstance();
        c.setTimeZone(new SimpleTimeZone(0, "UTC"));
        return c;
    }
    
    @Override
    public void set(PreparedStatement st, Object value, int index) throws SQLException {
        Timestamp ts;
        if (value instanceof Timestamp) {
            ts = (Timestamp) value;
        } else {
            ts = new Timestamp(((java.util.Date)value).getTime());
        }
        st.setTimestamp(index, ts, createUTCCalendar());
    }

}

Use it as follows with Java annotations (you could use the type class also in a XML configuration file):

import java.util.Date;
import org.hibernate.annotations.Type;

@Entity
@Table(name="...")
public class Data {

    private Date receptionTimeDt;
 
    @Type(type="ch.meteoswiss.commons.hibernate.UTCTimestampType")
    @Column(name="RECEPTION_TIME_DT", nullable=false)
    public Date getReceptionTimeDt() {
        return receptionTimeDt;
    }

}

Of course, this mapping class only works with Hibernate and is not standard JPA.