Java – In joda time how to convert time zone without changing time

For strings such as 2012-09-19 01:27:30.000, DateTime.Parse cannot tell what time zone the date and time are from.

DateTime has a Kind property, which can have one of three time zone options:

• Unspecified
• Local
• Utc

NOTE If you are wishing to represent a date/time other than UTC or your local time zone, then you should use DateTimeOffset.

So for the code in your question:

DateTime convertedDate = DateTime.Parse(dateStr);

var kind = convertedDate.Kind; // will equal DateTimeKind.Unspecified

You say you know what kind it is, so tell it.

DateTime convertedDate = DateTime.SpecifyKind(
    DateTime.Parse(dateStr),
    DateTimeKind.Utc);

var kind = convertedDate.Kind; // will equal DateTimeKind.Utc

Now, once the system knows its in UTC time, you can just call ToLocalTime:

DateTime dt = convertedDate.ToLocalTime();

This will give you the result you require.

Jon's answer talks about TimeZone, but I'd suggest using TimeZoneInfo instead.

Personally I like keeping things in UTC where possible (at least for the past; storing UTC for the future has potential issues), so I'd suggest a structure like this:

public struct DateTimeWithZone
{
    private readonly DateTime utcDateTime;
    private readonly TimeZoneInfo timeZone;

    public DateTimeWithZone(DateTime dateTime, TimeZoneInfo timeZone)
    {
        var dateTimeUnspec = DateTime.SpecifyKind(dateTime, DateTimeKind.Unspecified);
        utcDateTime = TimeZoneInfo.ConvertTimeToUtc(dateTimeUnspec, timeZone); 
        this.timeZone = timeZone;
    }

    public DateTime UniversalTime { get { return utcDateTime; } }

    public TimeZoneInfo TimeZone { get { return timeZone; } }

    public DateTime LocalTime
    { 
        get 
        { 
            return TimeZoneInfo.ConvertTime(utcDateTime, timeZone); 
        }
    }        
}

You may wish to change the "TimeZone" names to "TimeZoneInfo" to make things clearer - I prefer the briefer names myself.