How to Change Timezone for a Java.Util.Calendar/Date

How to change TIMEZONE for a java.util.Calendar/Date

In Java, Dates are internally represented in UTC milliseconds since the epoch (so timezones are not taken into account, that's why you get the same results, as getTime() gives you the mentioned milliseconds).

In your solution:

Calendar cSchedStartCal = Calendar.getInstance(TimeZone.getTimeZone("GMT"));
long gmtTime = cSchedStartCal.getTime().getTime();

long timezoneAlteredTime = gmtTime + TimeZone.getTimeZone("Asia/Calcutta").getRawOffset();
Calendar cSchedStartCal1 = Calendar.getInstance(TimeZone.getTimeZone("Asia/Calcutta"));
cSchedStartCal1.setTimeInMillis(timezoneAlteredTime);

you just add the offset from GMT to the specified timezone ("Asia/Calcutta" in your example) in milliseconds, so this should work fine.

Another possible solution would be to utilise the static fields of the Calendar class:

//instantiates a calendar using the current time in the specified timezone
Calendar cSchedStartCal = Calendar.getInstance(TimeZone.getTimeZone("GMT"));
//change the timezone
cSchedStartCal.setTimeZone(TimeZone.getTimeZone("Asia/Calcutta"));
//get the current hour of the day in the new timezone
cSchedStartCal.get(Calendar.HOUR_OF_DAY);

Refer to stackoverflow.com/questions/7695859/ for a more in-depth explanation.

How to set time zone of a java.util.Date?

Use DateFormat. For example,

SimpleDateFormat isoFormat = new SimpleDateFormat("yyyy-MM-dd'T'HH:mm:ss");
isoFormat.setTimeZone(TimeZone.getTimeZone("UTC"));
Date date = isoFormat.parse("2010-05-23T09:01:02");

How do I set a Calendar with TimeZone?

The problem here is that Java does not know of the timezone "EDT" (Eastern Daylight Time). As a result, Calendar seems to be setting the timezone to GMT.

The timezone needed here is "America/New_York" or "EST5EDT". When either of these values are used, the correct result is produced.

The list of valid Time Zones can be obtained by calling TimeZone.getAvailableIDs()

It is unfortunate that no warnings are produced when the requested Time Zone is not found.

How to handle calendar TimeZones using Java?

Thank you all for responding. After a further investigation I got to the right answer. As mentioned by Skip Head, the TimeStamped I was getting from my application was being adjusted to the user's TimeZone. So if the User entered 6:12 PM (EST) I would get 2:12 PM (GMT). What I needed was a way to undo the conversion so that the time entered by the user is the time I sent to the WebServer request. Here's how I accomplished this:

// Get TimeZone of user
TimeZone currentTimeZone = sc_.getTimeZone();
Calendar currentDt = new GregorianCalendar(currentTimeZone, EN_US_LOCALE);
// Get the Offset from GMT taking DST into account
int gmtOffset = currentTimeZone.getOffset(
    currentDt.get(Calendar.ERA), 
    currentDt.get(Calendar.YEAR), 
    currentDt.get(Calendar.MONTH), 
    currentDt.get(Calendar.DAY_OF_MONTH), 
    currentDt.get(Calendar.DAY_OF_WEEK), 
    currentDt.get(Calendar.MILLISECOND));
// convert to hours
gmtOffset = gmtOffset / (60*60*1000);
System.out.println("Current User's TimeZone: " + currentTimeZone.getID());
System.out.println("Current Offset from GMT (in hrs):" + gmtOffset);
// Get TS from User Input
Timestamp issuedDate = (Timestamp) getACPValue(inputs_, "issuedDate");
System.out.println("TS from ACP: " + issuedDate);
// Set TS into Calendar
Calendar issueDate = convertTimestampToJavaCalendar(issuedDate);
// Adjust for GMT (note the offset negation)
issueDate.add(Calendar.HOUR_OF_DAY, -gmtOffset);
System.out.println("Calendar Date converted from TS using GMT and US_EN Locale: "
    + DateFormat.getDateTimeInstance(DateFormat.SHORT, DateFormat.SHORT)
    .format(issueDate.getTime()));

The code's output is: (User entered 5/1/2008 6:12PM (EST)

Current User's TimeZone: EST

Current Offset from GMT (in hrs):-4 (Normally -5, except is DST adjusted)

TS from ACP: 2008-05-01 14:12:00.0

Calendar Date converted from TS using GMT and US_EN Locale: 5/1/08 6:12 PM (GMT)

Convert Date/Time for given Timezone - java

For me, the simplest way to do that is:

import java.text.SimpleDateFormat;
import java.util.Calendar;
import java.util.Date;
import java.util.TimeZone;

Calendar calendar = Calendar.getInstance();
calendar.setTime(new Date());
SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd hh:mm:ss");

//Here you say to java the initial timezone. This is the secret
sdf.setTimeZone(TimeZone.getTimeZone("UTC"));
//Will print in UTC
System.out.println(sdf.format(calendar.getTime()));    

//Here you set to your timezone
sdf.setTimeZone(TimeZone.getDefault());
//Will print on your default Timezone
System.out.println(sdf.format(calendar.getTime()));

How to create Calendar with specific TimeZone?

Just reverse the order of "specify date, specify time zone" to "specify time zone, specify date":

Calendar calendar = new GregorianCalendar(TimeZone.getTimeZone("UTC"));
calendar.set(2014, 0, 1, 0, 0, 0);
calendar.set(Calendar.MILLISECOND, 0);

I'd also recommend avoiding the Calendar/Date API entirely - use java.time for Java 8, and Joda Time for older versions of Java.

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