将SQL UTC时间戳转换为本地时区Java

Question

I have the following code. I have stored a utc time in my mySQL db and would like to convert it to local time when I pull it from the database.

        Instant startInstant = rs.getTimestamp(5).toInstant();
        Instant endInstant = rs.getTimestamp(6).toInstant();
        ZoneId z = ZoneId.of(TimeZone.getDefault().getID());

        ZonedDateTime start = startInstant.atZone(z);
        ZonedDateTime end = startInstant.atZone(z);


        System.out.println(start.format(DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss VV")));
        System.out.println(end.format(DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss VV")));

This is the output I get:

2017-11-01 01:40:00 America/Chicago
2017-11-01 01:40:00 America/Chicago

The date and time are the same as in my db: This is the field value in the table:

2017-11-01 01:40:00

The only thing that seems to have updated is just the zoneID to America/Chicago which is functionally useless for what I'm needing.

Any pointers as to where I've gone wrong?

Answer 1

You have not supplied enough information to give an exact Answer. You did not explain exactly the data type of the column around your date-time value. I suspect you did not use the MySQL equivalent to the SQL standard type of TIMESTAMP WITH TIME ZONE .

I also wonder why your example of a stored value lacks any offset-from-UTC or time zone. That is suspicious.

Lastly, you may be looking st your stored value by using an interactive SQL session with a default time zone bring dynamically applied to the value retrieved from the database before displaying in your session. While well-intentioned, I consider this an anti-feature as it masks the true nature of the stored data. This behavior may explain your confusion. Try explicitly setting your session's default time zone to UTC.

Other issues with your code…

Skip the use of java.sql.Timestamp altogether. If your JDBC driver supports JDBC 4.2 or later, you can work directly with the java.time types.

Instant instant = myResultSet.getObject( … , Instant.class ) ;

Do not mix an old legacy class like TimeZone with the modern java.time classes. The legacy classes are completely supplanted by java.time; good riddance.

ZoneId z = ZoneId.systemDefault() ;

Answer 2

You are getting the same value that you have entered in a database. You have timestamp values in database, but how you can say that the values stored are in UTC (the values might be in UTC but not in UTC format, so by looking into the value, you can't say that the value is in UTC -> '2017-11-01 01:40:00').

If you want to fetch the value in the different time zone, you can also do like this :

eg: SET time_zone ='+03:00'; SELECT value FROM table;

It will be providing you the value in specified time zone.