Retrieving UTC DATETIME field from MySQL in Java when server timezone is not UTC

Question

I'm trying to write code to interoperate with a third-party-developed database using Java and MySQL. This database has a field that stores a time stamp in a DATETIME field as a UTC date. The timezone for the server on which both the database and client run is set to a non-UTC zone (Europe/London), so by default the timestamp is read back incorrectly as if it were a local time. I'm trying to write code to read it back as UTC.

I have read several similar questions here, but none of them have an answer that works for me:

• MySQL - how to store time with correct timezone? (from Java)
• How to store a java.util.Date into a MySQL timestamp field in the UTC/GMT timezone?
• Date in UTC in mysql
• How do I set the time zone of MySQL?

Unfortunately, I cannot change any server settings, so I have tried using the connection's "time_zone" variable to set the database server to use UTC and the optional Calendar parameter to ResultSet.getTimestamp to retrieve the date, but this has no effect on the result. Here is my code:

private static final Calendar UTCCALENDAR = Calendar.getInstance (TimeZone.getTimeZone (ZoneOffset.UTC));
public Date getDate ()
{
    try (Connection c = dataSource.getConnection ();
         PreparedStatement s = c
             .prepareStatement ("select datefield from dbmail_datefield where physmessage_id=?"))
    {
        fixTimeZone (c);
        s.setLong (1, getPhysId ());
        try (ResultSet rs = s.executeQuery ())
        {
            if (!rs.next ()) return null;
            return new Date (rs.getTimestamp(1,UTCCALENDAR).getTime ());    // do not use SQL timestamp object, as it fucks up comparisons!
        }
    }
    catch (SQLException e)
    {
        throw new MailAccessException ("Error accessing dbmail database", e);
    }
}

private void fixTimeZone (Connection c)
{
    try (Statement s = c.createStatement ())
    {
        s.executeUpdate ("set time_zone='+00:00'");
    }
    catch (SQLException e)
    {
        throw new MailAccessException ("Unable to set SQL connection time zone to UTC", e);
    }
}

The database field I'm trying to read has a value stored in it as follows:

mysql> select * from dbmail_datefield where physmessage_id=494539;
+----------------+--------+---------------------+
| physmessage_id | id     | datefield           |
+----------------+--------+---------------------+
|         494539 | 494520 | 2015-04-16 10:30:30 |
+----------------+--------+---------------------+

But unfortunately, the result comes out as BST not UTC:

java.lang.AssertionError: expected:<Thu Apr 16 11:30:30 BST 2015> but was:<Thu Apr 16 10:30:30 BST 2015>

Answer 1

Your client getDate() code looks correct as far as it goes. I think you also need to get the MySQL Connector/J JDBC driver to treat the dates stored in the table as UTC dates, to avoid a spurious time zone conversion. This means setting the effective server time zone, in addition to the client session time zone and Calendar used for JDBC getTimestamp calls as you're doing.

Take a look at the values you got in your failed assertion, and which direction the error is in:

expected:<Thu Apr 16 11:30:30 BST 2015> but was:<Thu Apr 16 10:30:30 BST 2015>

What you got back was 10:30 BST, which is 9:30 GMT. This is consistent with the database treating that 10:30 in the table as a BST value and spuriously converting it to GMT for you, before you parse it as a GMT date. That's the opposite direction of a GMT value being spuriously converted to BST.

This may be a JDBC-specific issue, because JDBC requires that time times be converted to the local zone. (Where the MySQL C API doesn't, probably because C's classic time types are not zone-aware the way Java's are.) And it needs to know what zone it's converting from, as well. The MySQL TIMESTAMP type is always stored as UTC. But that's not stated for the DATETIME type. I think that implies that MySQL is going to interpret DATETIME column values as being in the server's time zone. Which you mentioned as being set to BST, and that's consistent with the direction of the shift shown in your assertion error message.

The time_zone session variable you set is telling the MySQL server what your client machine's time zone is, but it doesn't affect what the server thinks its own time zone is. That can be overridden with the serverTimezone JDBC connection property. On your connection, set the serverTimezone to UTC, and make sure useLegacyDatetimeCode is off. (And look through the other zone-related properties if that doesn't work.) See if that gets your dates to come through as UTC with the same calendar field values as in the database.

Be aware that this is going to change the interpretation of other DATETIME values in your database: they're all going to look like UTC dates now (in the context of your JDBC connection). Whether that's correct is going to depend on how they were populated initially. While your client code will have the behavior you want, I don't know if this system as a whole can be made to behave fully consistently without setting the server's time zone to UTC at the server level. Basically, if it doesn't have its zone set to UTC, it's not fully configured for the behavior you want, and you're kludging around it.

Answer 2

If you want to use timezone you can read column as UTC.

ZonedDateTime zdt = ZonedDateTime.of(rs.getTimestamp(1).toLocalDateTime(), ZoneOffset.UTC);

Next you can change to whatever timezone you want using:

zdt = zdt.withZoneSameInstant(ZoneId.of(
            TARGET_ZONE));

If you want only to read Date and do not care about zones at all use only:

LocalDateTime ldt = rs.getTimestamp(1).toLocalDateTime()

You will obtain LocalDateTime without timezone.

If you have to return java.util.Date use:

Date.from(ldt.atZone(ZoneOffset.UTC).toInstant());

Answer 3

Your best bet, in my view, is to tell MySQL to use GMT and handle all local time issues in your application code, not your database. The values in the database would always be GMT, full stop, which is unambiguous. As you say, with daylight savings time (summer time) adjustments, you can end up with the same value in your database for what is, to us humans, two different times.

This also makes the database portable. If you move to North America and start using MySQL set to (say) Central time, all of a sudden the values in your database seem to have moved several hours. I had that issue with a database I inherited which was using the server's local time, when I moved it from the east coast of the U.S. to the west coast, not having thought to check whether MySQL was slaved to the machine's zone...

long t = 1351382400000; // the timestamp in UTC
String insert = "INSERT INTO my_table (timestamp) VALUES (?)";
PreparedStatement stmt = db.prepareStatement(insert);
java.sql.Timestamp date = new Timestamp(t);
stmt.setTimestamp(1, date);
stmt.executeUpdate();

.....

TimeZone timezone = TimeZone.getTimeZone("MyTimeZoneId");
Calendar cal = java.util.Calendar.getInstance(timezone);
String select = "SELECT timestamp FROM my_table";
// some code omitted....
ResultSet rs = stmt.executeQuery();
while (rs.next()) {
   java.sql.Timestamp ts = rs.getTimestamp(1);
   cal.setTimeInMillis(ts.getTime());
   System.out.println("date in db: " + cal.getTime());
}

Answer 4

Don't think about converting or adapting time zone. Don't think about the TZ the mysql uses to store your timestamps or anythink like that. Those things are already handled. There are three things that you must handle: INPUT, OUTPUT and bugs.

INPUT

When a user enters a date (in a form) without an explicit time zone you have to know what TZ did he intend to use. You can use a SimpleDateFormat object with time zone set to solve this. You don't have to convert the input date, you have to 'interpret' it correctly. Once you have a correctly interpreted Date or timestamp you are done with input.

Input is not only user input, includes configuration files too.

OUTPUT

The same here. Forget about what TZ have your Date objects and timestamps have none, they are just milliseconds since epoch. You have to format your dates to the TZ the user expects so he understand them.

Bugs

You may have bugs in your code related to TZ, but libraries may have them too!!

I noticed mysql java driver failed to communicate the client timezone to the server. This command s.executeUpdate ("set time_zone='+xx:yy'"); is the workaround but you are using it wrong. You have to tell the server with it the TZ the client is using, before both inserting and querying. The variable is stored in the session. Maybe you may automatize it on your connection pool config. This is needed so the server know what TZ the client need to use to read or write. This is not dependent on server TZ. It does not mean "store this date in UTC", it does mean "this date I am giving to you is UTC" and "Send me result sets in UTC". No matter you are using Date class with it's internal TZ, the driver screws it up, you would need to set that session variable.

By default it assumes client TZ is the same as server TZ so you shouldn't need to worry about it as you said they are the same.

Answer 5

Maybe you can use JodaTime as follows;

private static final Calendar UTCCALENDAR = Calendar.getInstance (TimeZone.getTimeZone (ZoneOffset    .UTC));
public Date getDate ()
{
    try (Connection c = dataSource.getConnection ();
         PreparedStatement s = c
             .prepareStatement ("select datefield from dbmail_datefield where physmessage_id=?"))
    {
        s.setLong (1, getPhysId ());
        try (ResultSet rs = s.executeQuery ())
        {
            if (!rs.next ()) return null;
            DateTime dt = new LocalDateTime(rs.getTimestamp(1,UTCCALENDAR).getTime ()).toDateTime(DateTimeZone.forID("Europe/London"));  

            return dt.toDate();               }
    }
    catch (SQLException e)
    {
        throw new MailAccessException ("Error accessing dbmail database", e);
    }
}

EDIT:

java.util.Date is not TimeZone agnostic. The method toDateTime takes care of TimeZone and DST so you don't care about it

The following code:

public static void main(String[] args) {
    // 29/March/2015 1:05 UTC
    DateTime now = new DateTime(2015, 3,29,1,5,DateTimeZone.UTC);
    // Pre DST 29/March/2015 0:30 UTC
    DateTime preDst = new DateTime(2015, 3,29,0,30,DateTimeZone.UTC);
    System.out.println("1:05 UTC:"+now);
    System.out.println("0:30 UTC:"+preDst);
    DateTimeZone europeDTZ = DateTimeZone.forID("Europe/London");
    DateTime europeLondon = now.toDateTime(europeDTZ);
    System.out.println("1:05 UTC as Europe/London:"+europeLondon);
    DateTime europeLondonPreDst = preDst.toDateTime(europeDTZ);
    System.out.println("0:30 UTC as Europe/London:"+europeLondonPreDst);
}

Will print:

1:05 UTC:2015-03-29T01:05:00.000Z
0:30 UTC:2015-03-29T00:30:00.000Z
1:05 UTC as Europe/London:2015-03-29T02:05:00.000+01:00
0:30 UTC as Europe/London:2015-03-29T00:30:00.000Z

If you can see JodaTime takes care of DST.