在 sql 服务器中使用 UTC 时间保存当前日期的问题

Question

I want save date with UTC time zone in sql server 2014. I have used ZonedDateTime zonedDateTime = ZonedDateTime.now(ZoneId.of("UTC")) to get the current date time and persisting this to db using Hibernate session object. While debugging I can see that in Java program date is fine like this 2019-09-25T13:22:29.573Z[UTC] , but after saving in database column it is something like this 2019-09-25 18:53:23.3630000 . It's automatically converting the time part according to system time. Can anyone please suggest what is the issue? I have used datetime2 datatype while creating this column in database.

Answer 1

Wrong type

You are using the wrong data type for your column.

The type datetime2 cannot represent a moment. That type stores only a date and a time-of-day, but lacks the context of a time zone or offset-from-UTC. So if you store “noon on the 23rd of January in 2020”, we cannot know if you meant noon in Tokyo Japan, noon in Tunis Tunisia, or noon in Toledo Ohio US, three different moments several hours apart. This wrong type is akin to the SQL standard type TIMESTAMP WITHOUT TIME ZONE . The equivalent class in Java is LocalDateTime .

If you already have data stored, you will need to refactor your database . Basically, add a new column of the correct type, copy data over for each row, converting as you go. Of course, this only works if you know the intended time zone that was absent from each value saved.

Right type

While I don't use Microsoft SQL Server, according to the doc you should be using a column of type datetimeoffset to record a moment . This type adjusts any submitted value into UTC for queries and sorting, while also recording the offset. This type is akin to the SQL standard type TIMESTAMP WITH TIME ZONE .

Generally best to store your moments in UTC, an offset of zero hours-minutes-seconds.

The Instant class represents a moment in UTC.

Instant instant = Instant.now() ;

If you have a ZonedDateTime , you can extract an Instant .

Instant instant = zdt.toInstant() ;

We would like to save that Instant directly to the database. Unfortunately the JDBC 4.2 soec does not require support for either of the two most commonly used java.time classes: Instant and ZonedDateTime . The spec does require support for OffsetDateTime . So we convert.

OffsetDateTime odt = instant.atOffset( ZoneOffset.UTC ) ;

Submit to database.

myPreparedStatement.setObject( … , odt ) ; 

Retrieve.

OffsetDateTime odt = MyResultSet.getObject( … , OffsetDateTime.class ) ;

Extract an Instant to make clear in your code that you want UTC.

Instant instant = odt.toInstant() ;

See this moment through the wall-clock-time used by the people of a particular region (a time zone).

ZoneId z = ZoneId.of( "Asia/Kolkata" ) ;
ZonedDateTime zdt = instant.atZone( z ) ;

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