Reputation: 7244
I'm trying to convert some string that is in UTC time to a java Calendar object that should be set to GMT-5.
My current UTC string input is this:
UTC date : 20050329174411
I use this code (I detect the 'pattern' as shown below):
DateFormat dateFormat = new SimpleDateFormat(pattern);
Date date = dateFormat.parse(utcDate);
calendar = Calendar.getInstance(TimeZone.getTimeZone("GMT-5"));
calendar.setTime(date);
I then printed the time like this:
calendar.getTime()
And I got this result:
GMT date : Tue Mar 29 17:44:11 EST 2005
I need to support theses date/time string patterns:
FORMAT_UTC4 = "yyyy";
FORMAT_UTC6 = "yyyyMM";
FORMAT_UTC8 = "yyyyMMdd";
FORMAT_UTC10 = "yyyyMMddHH";
FORMAT_UTC12 = "yyyyMMddHHmm";
FORMAT_UTC14 = "yyyyMMddHHmmss";
I would be expecting the time to be set to "12:44:11". I have read a couple of examples and I find date time handling pretty confusing. For me, it's always the same, I get some sort of string formatted UTC and I convert it to GMT-5. I really feel it should be easy!
Ref 1 : How can I get the current date and time in UTC or GMT in Java?
Ref 2 : How to handle calendar TimeZones using Java?
Upvotes: 4
Views: 5405
Reputation: 79115
Note that GMT-5
or timezone offset of -05:00
hours is a fixed offset i.e. independent of the DST and type to represent a date-time with timezone offset is OffsetDateTime
.
Demo:
import java.time.Instant;
import java.time.OffsetDateTime;
import java.time.ZoneOffset;
public class Main {
public static void main(String[] args) {
Instant instant = Instant.ofEpochMilli(20050329174411L);
OffsetDateTime odt = instant.atOffset(ZoneOffset.of("-05:00"));
// Alternatively
// OffsetDateTime.ofInstant(instant, ZoneOffset.of("-05:00"));
System.out.println(odt);
}
}
Output:
2605-05-15T18:52:54.411-05:00
If you are looking for an automatic adjustment of timezone offset as per the DST, use ZonedDateTime
.
Demo:
import java.time.Instant;
import java.time.ZoneId;
import java.time.ZonedDateTime;
public class Main {
public static void main(String[] args) {
Instant instant = Instant.ofEpochMilli(20050329174411L);
ZonedDateTime zdt = instant.atZone(ZoneId.of("America/Chicago"));
// Alternatively
// ZonedDateTime.ofInstant(instant, ZoneId.of("America/Chicago"));
System.out.println(zdt);
}
}
Output:
2605-05-15T18:52:54.411-05:00[America/Chicago]
Learn more about java.time
, the modern date-time API* from Trail: Date Time.
If at all you need an object of java.util.Calendar
from this object of ZonedDateTime
, you can do so as follows:
Calendar calendar = Calendar.getInstance();
calendar.setTime(Date.from(zdt.toInstant()));
* For any reason, if you have to stick to Java 6 or Java 7, you can use ThreeTen-Backport which backports most of the java.time functionality to Java 6 & 7. If you are working for an Android project and your Android API level is still not compliant with Java-8, check Java 8+ APIs available through desugaring and How to use ThreeTenABP in Android Project.
Upvotes: 0
Reputation: 691835
You must set the SimpleDateFormat's time zone to UTC before parsing the date. Else, it uses your default timezone.
And to display the date in the "GMT-5" timezone, you should use another DateFormat, with the timezone set to GMT-5, and format the date with this DateFormat. The toString()
method of Date uses your default time zone to transform the date into something readable.
Upvotes: 5