Develop Reference

Calendar in Java is not working for UTC timezone

My code:
TimeZone timeZone = TimeZone.getTimeZone("UTC");
Calendar cal = (Calendar) Calendar.getInstance(timeZone);
SimpleDateFormat simpleDateFormat = new SimpleDateFormat("EE MMM dd HH:mm:ss zzz yyyy", Locale.US);
System.out.println("Gregorian cal time:"+cal.getTime());
System.out.println("utc time: "+simpleDateFormat.format(cal.getTime()));
Both the print statements are showing the same local time.

You need to set the TimeZone of your DateFormatter to "UTC"
SimpleDateFormat simpleDateFormat = new SimpleDateFormat("EE MMM dd HH:mm:ss zzz yyyy", Locale.US);
simpleDateFormat.setTimeZone(TimeZone.getTimeZone("UTC"));
System.out.println("utc time: "+simpleDateFormat.format(cal.getTime()));

LocalDateTime utc_time = LocalDateTime.now(ZoneId.of("UTC"));
System.out.println("Date: "+utc_time);
works fine

tl;dr
Instant.now()
Avoid legacy date-time classes
You are using troublesome old date-time classes, now legacy, supplanted by the java.time classes. The legacy classes are an awful mess, poorly designed, confusing, and flawed. Avoid them.
Instant
The Instant class represents a moment on the timeline in UTC with a resolution of nanoseconds (up to nine (9) digits of a decimal fraction).
Instant instant = Instant.now();
instant.toString(): 2017-02-23T03:30:58.431Z
The format of that string generated by toString is standard ISO 8601 format. The Z on the end is short for Zulu and means UTC.
That's it, you are done.
ZonedDateTime
If you want to see that same moment as the wall-clock time of some particular region, then apply a ZoneId to get a ZonedDateTime.
Specify a proper time zone name in the format of continent/region, such as America/Montreal, Africa/Casablanca, or Pacific/Auckland. Never use the 3-4 letter abbreviation such as EST or IST as they are not true time zones, not standardized, and not even unique(!).
ZoneId z = ZoneId.of( "Asia/Kolkata" );
ZonedDateTime zdt = instant.atZone( z );
zdt.toString(): 2017-02-23T09:00:58.431+05:30[Asia/Kolkata]
India is five and a half hours ahead of UTC. So when adjusted into Asia/Kolkata time zone, note how the time-of-day jumps from 03:30 to 09:00.
About java.time
The java.time framework is built into Java 8 and later. These classes supplant the troublesome old legacy date-time classes such as java.util.Date, Calendar, & SimpleDateFormat.
The Joda-Time project, now in maintenance mode, advises migration to the java.time classes.
To learn more, see the Oracle Tutorial. And search Stack Overflow for many examples and explanations. Specification is JSR 310.
Where to obtain the java.time classes?
Java SE 8 and SE 9 and later
Built-in.
Part of the standard Java API with a bundled implementation.
Java 9 adds some minor features and fixes.
Java SE 6 and SE 7
Much of the java.time functionality is back-ported to Java 6 & 7 in ThreeTen-Backport.
Android
The ThreeTenABP project adapts ThreeTen-Backport (mentioned above) for Android specifically.
See How to use ThreeTenABP….
The ThreeTen-Extra project extends java.time with additional classes. This project is a proving ground for possible future additions to java.time. You may find some useful classes here such as Interval, YearWeek, YearQuarter, andfz more.

Format a Date String with Time zone and return Date object

I need to format a string date with given time zone and return the date object back. I am currently in IST time zone.
So IST is 5 hours and 30 minutes ahead of UTC.
public void getDate(){
String dateStr = "11/25/2016T13:30:00.000";
String dateFormat = "MM/dd/yyyy'T'HH:mm:ss.SSS";
Date date = formatedStringToDate(dateStr, dateFormat);
System.out.println(date);
}
public static Date formatedStringToDate(final String date, final String dateFormat) throws ParseException {
final SimpleDateFormat sdf = new SimpleDateFormat(dateFormat);
sdf.setTimeZone(TimeZone.getTimeZone("UTC"));
Date parsedDate = null;
if (date != null) {
try {
parsedDate = sdf.parse(date);
} catch (ParseException e) {
throw e;
}
}
return parsedDate;
}
I get the below out put.
Fri Nov 25 19:00:00 **IST** 2016
The time seems to be change from 5.30 hours but then if its a IST to UCT time converstion, it should be 5.30 hours before 13:30:00 which is 08:00:00?
Also how could I change the highlighted IST part of out put string to show the currect time zone in this case UTC?

When you call toString on a Date (by printing it) you get the default format (because a Date is an object that stores a number of milliseconds, or nanoseconds in Java 9+, since an epoch). To see the result in UTC you need something like,
final DateFormat sdf = DateFormat.getDateTimeInstance(DateFormat.FULL,
DateFormat.FULL);
sdf.setTimeZone(TimeZone.getTimeZone("UTC"));
Date date = formatedStringToDate(dateStr, dateFormat);
System.out.println(sdf.format(date)); // <-- format the Date

tl;dr
LocalDateTime.parse( "2017-11-25T13:30:00.000" )
.atZone( ZoneId.of( "Asia/Kolkata" ) )
2017-11-25T13:30+05:30[Asia/Kolkata]
java.time
The modern approach uses the java.time classes that replaced the troublesome old legacy date-time classes.
Parse your input string as a LocalDateTime given the lack of any indicator of zone or offset-from-UTC.
Using standard ISO 8601 format for such strings is preferred. The java.time classes use the standard formats by default when parsing/generating strings.
LocalDateTime ldt = LocalDateTime.parse( "2017-11-25T13:30:00.000" ) ;
ldt.toString(): 2017-11-25T13:30
If you are certain this date-time was intended to represent a moment by the wall-clock time of India, then assign a time zone to produce a ZonedDateTime object.
Specify a proper time zone name in the format of continent/region, such as America/Montreal, Africa/Casablanca, or Pacific/Auckland. Never use the 3-4 letter abbreviation such as EST or IST as they are not true time zones, not standardized, and not even unique(!).
ZoneId z = ZoneId.of( "Asia/Kolkata" ) ;
ZonedDateTime zdt = ldt.atZone( z ) ;
zdt.toString(): 2017-11-25T13:30+05:30[Asia/Kolkata]
You can adjust into another zone for comparison.
ZonedDateTime zdtMontreal = zdt.withZoneSameInstant( ZoneId.of( "America/Montreal") );
zdtMontreal.toString(): 2017-11-25T03:00-05:00[America/Montreal]
To parse/generate strings in other formats such as the one in your Question, use the DateTimeFormatter or DateTimeFormatterBuilder classes. Search Stack Overflow for more info, as these have been covered extensively.
DateTimeFormatter f = DateTimeFormatter.ofPattern( "MM/dd/uuuu'T'HH:mm:ss.SSS" , Locale.US ) ;
Use that formatter for parsing.
LocalDateTime ldt = LocalDateTime.parse( "11/25/2016T13:30:00.000" , f ) ;
And for generating.
String output = ldt.format( f ) ; // Generate string.
Consider using ISO 8601 formats instead.
About java.time
The java.time framework is built into Java 8 and later. These classes supplant the troublesome old legacy date-time classes such as java.util.Date, Calendar, & SimpleDateFormat.
The Joda-Time project, now in maintenance mode, advises migration to the java.time classes.
To learn more, see the Oracle Tutorial. And search Stack Overflow for many examples and explanations. Specification is JSR 310.
With a JDBC driver complying with JDBC 4.2 or later, you may exchange java.time objects directly with your database. No need for strings or java.sql.* classes.
Where to obtain the java.time classes?
Java SE 8, Java SE 9, and later
Built-in.
Part of the standard Java API with a bundled implementation.
Java 9 adds some minor features and fixes.
Java SE 6 and Java SE 7
Much of the java.time functionality is back-ported to Java 6 & 7 in ThreeTen-Backport.
Android
Later versions of Android bundle implementations of the java.time classes.
For earlier Android, the ThreeTenABP project adapts ThreeTen-Backport (mentioned above). See How to use ThreeTenABP….
The ThreeTen-Extra project extends java.time with additional classes. This project is a proving ground for possible future additions to java.time. You may find some useful classes here such as Interval, YearWeek, YearQuarter, and more.

Java library function for converting from gregorian timestamp to UNIX timestamp(epoch) [duplicate]

I am getting time in string like this "2011-02-27T10:03:33.099-06:00" which is of xml dateTime type. I also have timezone of TimeZone type. How should I convert the dateTime to GregorianCalendar java type in that timezone.

Java has built in code to parse xml datetimes: use DatatypeConverter.parseDateTime(). that will return a Calendar in the parsed TimeZone. you can then set the Calendar TimeZone to your desired target TimeZone for whatever you need to do next.

sdf = new java.text.SimpleDateFormat ("yyyy-MM-dd'T'HH:mm:ss.S");
parses everything, except the trailing TZ.
sdf.parse (sd);
res168: java.util.Date = Sun Feb 27 10:03:33 CET 2011
From the api docs, I would expect
sdf = new java.text.SimpleDateFormat ("yyyy-MM-dd'T'HH:mm:ss.SSSz");
to be used to read the -06:00 in the end. But I see, that there is either an offset in the form 0700 expected, or with a prefix of GMT for example "GMT-04:00". So you have to insert that GMT-thingy yourself:
sdf.parse (sd.replaceAll ("(......)$", "GMT$1"))
SDF.parse (str) returns a Date, which has to be converted into a GC:
GregorianCalendar calendar = new GregorianCalendar ();
calendar.setTime (date);

tl;dr
OffsetDateTime.parse( "2011-02-27T10:03:33.099-06:00" )
java.time
The modern approach uses the java.time classes that supplanted the troublesome old legacy date-time classes. Specifically, GregorianCalendar was replaced by ZonedDateTime for a time zone, and OffsetDateTime for a mere offset-from-UTC.
ISO 8601
Your input string happens to comply with the ISO 8601 standard format.
The java.time classes use these standard formats by default when parsing/generating strings. So no need to specify a formatting pattern.
OffsetDateTime
Your input string contains an offset-from-UTC, but not a time zone. So parse as an OffsetDateTime.
OffsetDateTime odt = OffsetDateTime.parse( "2011-02-27T10:03:33.099-06:00" ) ;
ZonedDateTime
If you know for certain the intended time zone, apply a ZoneId to produce a ZonedDateTime.
A time zone is always preferable to a mere offset. A zone is a history of past, present, and future changes to the offset used by the people of a particular region.
Specify a proper time zone name in the format of continent/region, such as America/Montreal, Africa/Casablanca, or Pacific/Auckland. Never use the 3-4 letter abbreviation such as EST or IST as they are not true time zones, not standardized, and not even unique(!).
ZoneId z = ZoneId.of( "Pacific/Galapagos" ) ;
ZonedDateTime zdt = odt.atZoneSameInstant( z ) ;
Converting legacy ↔ modern
If you must have a GregorianCalendar object to inter-operate with old code not yet updated to java.time, you can convert. Look to new methods added to the old classes.
GregorianCalendar myGregCal = GregorianCalendar.from( zdt ) ;
And going the other direction…
ZonedDateTime zdt = myGregCal.toZonedDateTime() ;
About java.time
The java.time framework is built into Java 8 and later. These classes supplant the troublesome old legacy date-time classes such as java.util.Date, Calendar, & SimpleDateFormat.
The Joda-Time project, now in maintenance mode, advises migration to the java.time classes.
To learn more, see the Oracle Tutorial. And search Stack Overflow for many examples and explanations. Specification is JSR 310.
Using a JDBC driver compliant with JDBC 4.2 or later, you may exchange java.time objects directly with your database. No need for strings nor java.sql.* classes.
Where to obtain the java.time classes?
Java SE 8, Java SE 9, and later
Built-in.
Part of the standard Java API with a bundled implementation.
Java 9 adds some minor features and fixes.
Java SE 6 and Java SE 7
Much of the java.time functionality is back-ported to Java 6 & 7 in ThreeTen-Backport.
Android
Later versions of Android bundle implementations of the java.time classes.
For earlier Android, the ThreeTenABP project adapts ThreeTen-Backport (mentioned above). See How to use ThreeTenABP….
The ThreeTen-Extra project extends java.time with additional classes. This project is a proving ground for possible future additions to java.time. You may find some useful classes here such as Interval, YearWeek, YearQuarter, and more.

Java Date Format Parsing

I am trying to change the date format from a JSON response, but I keep getting java.text.ParseException.
This is the date from the server 2015-02-03T08:37:38.000Z and I want it to show as 2015/02/03 That's yyyy-MM-dd. And I did this.
DateFormat df1 = new SimpleDateFormat("yyyy-MM-dd'T'HH:mm:ss.SSSZ");
SimpleDateFormat dateFormatter = new SimpleDateFormat("yyyy-MM-dd");
String dateResp = transactionItem.get(position).getDate();
try {
Date date = df1.parse(dateResp);
transDate.setText(dateFormatter.format(date));
} catch (ParseException e) {
e.printStackTrace();
}
But the exception keeps showing.

You must escape the Z:
"yyyy-MM-dd'T'HH:mm:ss.SSS'Z'"
Try to use this for formatting purpose instead of your provided formatting string. It should work nicely :)

tl;dr
Instant.parse( "2015-02-03T08:37:38.000Z" )
.atZone( ZoneId.of( "America/Montreal" ) )
.toLocalDate()
.toString() // 2015-02-03
Using java.time
The modern way to handle date-time work is with the java.time classes.
Your input string format happens to comply with the ISO 8601 standard. The java.time classes use ISO 8601 formats by default when parsing/generating strings that represent date-time values. So no need to specify a formatting pattern at all.
Parse that string as an Instant. The Instant class represents a moment on the timeline in UTC with a resolution of nanoseconds (up to nine (9) digits of a decimal fraction).
Instant instant = Instant.parse( "2015-02-03T08:37:38.000Z" ) ;
To extract a date, you must specify a time zone. For any given moment the date varies around the globe by zone. For example, a moment after midnight in Paris France is a new day while still “yesterday” in Montréal Canada.
ZoneId z = ZoneId.of( "America/Montreal" );
ZonedDateTime zdt = instant.atZone( z );
You want only the date portion without the time of day. So extract a LocalDate. While a LocalDate lacks any concept of offset-from-UTC or time zone, the toLocalDate method respects the ZonedDateTime object’s time zone in determining the date.
LocalDate ld = zdt.toLocalDate();
You seem to want standard ISO 8601 format, YYYY-MM-DD. Simply call toString without need to specify a formatting pattern.
String output = ld.toString();
2015-02-03
About java.time
The java.time framework is built into Java 8 and later. These classes supplant the troublesome old legacy date-time classes such as java.util.Date, Calendar, & SimpleDateFormat.
The Joda-Time project, now in maintenance mode, advises migration to the java.time classes.
To learn more, see the Oracle Tutorial. And search Stack Overflow for many examples and explanations. Specification is JSR 310.
Where to obtain the java.time classes?
Java SE 8 and SE 9 and later
Built-in.
Part of the standard Java API with a bundled implementation.
Java 9 adds some minor features and fixes.
Java SE 6 and SE 7
Much of the java.time functionality is back-ported to Java 6 & 7 in ThreeTen-Backport.
Android
The ThreeTenABP project adapts ThreeTen-Backport (mentioned above) for Android specifically.
See How to use ThreeTenABP….
The ThreeTen-Extra project extends java.time with additional classes. This project is a proving ground for possible future additions to java.time. You may find some useful classes here such as Interval, YearWeek, YearQuarter, and more.

Convert IST to PST in java

Hi
I have a date/Time field i want to get Convert current IST to CURRENT PST in java... need help....
ex: now in IST its :13/may/2011 3.32.58pm want the same in PST i.e. 13/may/2011 3.02.58 AM
thank you........

If you're interested in the current time, you don't need to know about IST at all... just the current instance, and the conversion to PST. You can do this with something like:
Date now = new Date();
TimeZone zone = TimeZone.getTimeZone("America/Los_Angeles"); // For example...
DateFormat format = new SimpleDateFormat("..."); // Put your pattern here
format.setTimeZone(zone);
String text = format.format(now);
Personally I'd recommend you use Joda Time for all date/time work instead, as it's a much nicer API - but in this case it's really pretty simple even with the built-in API.

The Answer by Jon Skeet is correct but now outdated with the arrival of the java.time code in Java 8 and later.
java.time
The Instant class represents a moment on the timeline in UTC with a resolution of nanoseconds (up to nine (9) digits of a decimal fraction).
Get current moment in UTC.
Instant instant = Instant.now();
Adjust into a time zone.
Specify a proper time zone name in the format of continent/region, such as America/Montreal, Africa/Casablanca, or Pacific/Auckland. Never use the 3-4 letter abbreviation such as EST or IST as they are not true time zones, not standardized, and not even unique(!).
ZoneId z = ZoneId.of( "America/Los_Angeles" );
ZonedDateTime zdt = instant.atZone( z );
To generate a String in standard ISO 8601 format, call the toString. For alternate formatting, use the DateTimeFormatter class already covered in many other Questions and Answers.
String output = zdt.format( myDateTimeFormatter );
See the same moment in India time, specifically Asia/Kolkata.
ZoneId zKolkata = ZoneId.of( "Asia/Kolkata" );
ZonedDateTime zdtKolkata = zdt.withZoneSameInstant( zKolkata );
I am not sure if by IST you meant India Standard Time or Irish Standard Time. Let's cover Europe/Dublin as well. That zone happens to currently use an offset of zero, +00:00. So its wall-clock time in the same as UTC.
ZoneId zDublin = ZoneId.of( "Europe/Dublin" );
ZonedDateTime zdtDublin = zdt.withZoneSameInstant( zDublin );
See this code run live at IdeOne.com.
instant.toString(): 2017-02-13T07:28:57.738Z
zdt.toString(): 2017-02-12T23:28:57.738-08:00[America/Los_Angeles]
zdtKolkata.toString(): 2017-02-13T12:58:57.738+05:30[Asia/Kolkata]
zdtDublin.toString(): 2017-02-13T07:28:57.738Z[Europe/Dublin]
About java.time
The java.time framework is built into Java 8 and later. These classes supplant the troublesome old legacy date-time classes such as java.util.Date, Calendar, & SimpleDateFormat.
The Joda-Time project, now in maintenance mode, advises migration to the java.time classes.
To learn more, see the Oracle Tutorial. And search Stack Overflow for many examples and explanations. Specification is JSR 310.
Where to obtain the java.time classes?
Java SE 8 and SE 9 and later
Built-in.
Part of the standard Java API with a bundled implementation.
Java 9 adds some minor features and fixes.
Java SE 6 and SE 7
Much of the java.time functionality is back-ported to Java 6 & 7 in ThreeTen-Backport.
Android
The ThreeTenABP project adapts ThreeTen-Backport (mentioned above) for Android specifically.
See How to use ThreeTenABP….
The ThreeTen-Extra project extends java.time with additional classes. This project is a proving ground for possible future additions to java.time. You may find some useful classes here such as Interval, YearWeek, YearQuarter, and more.