How to convert date and time to user timezone

Question

Calendar cal = Calendar.getInstance();
cal.setTimeZone(TimeZone.getTimeZone("PST"));
cal.setTime(new Date());

SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd hh:mm:ss a");

Date resultdate = new Date(cal.getTimeInMillis());
sdf.setTimeZone(TimeZone.getTimeZone("PST"));

System.out.println("String date:"+sdf.format(resultdate));
System.out.println("Date:"+sdf.parse(sdf.format(resultdate)));

output:

String date:2011-12-29 09:01:58 PM                                               
Date:Fri Dec 30 10:31:58 IST 2011

Problem:

1. sdf.format(resultdate) returning correct date and time to as per timezone. But,
2. sdf.parse(sdf.format(resultdate)) not returning correct date and time to as per timezone, how to fix this problem?

Answer 1

The Date class is merely a thin wrapper around the number of milli-seconds past the 'epoch' (January 1, 1970, 00:00:00 GMT). It doesn't store any timezone information. In your last call you are adding a date instance to a String which implicitly calls the toString() method. The toString() method will use the default timezone to create a String representing the instance (as it doesn't store any timezone info). Try modifying the last line to avoid using the toString() method.

System.out.println("Date:" + sdf.format(sdf.parse(sdf.format(resultdate))));

Answer 2

Try using joda-Time api for your convenience. Example is here

Answer 3

try the below code will, it will work.

Calendar cal = Calendar.getInstance();
cal.setTimeZone(TimeZone.getTimeZone("PST"));
cal.setTime(new Date());

SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd hh:mm:ss a");
SimpleDateFormat sdf2 = new SimpleDateFormat("yyyy-MM-dd hh:mm:ss a");

Date resultdate = new Date(cal.getTimeInMillis());
sdf.setTimeZone(TimeZone.getTimeZone("PST"));

System.out.println("String date:"+sdf.format(resultdate));
System.out.println("Date:"+sdf2.parse(sdf.format(resultdate)));

Answer 4

Three-Letter Time Zone Codes

Avoid using the three-letter time zone codes. They are neither standardized nor unique. For example, IST means both India Standard Time and Irish Standard Time. Furthermore, the codes are meant to distinguish Daylight Saving Time (DST) but that only confuses matters.

Use proper descriptive time zone names to retrieve a time zone object that encompasses DST and other issues.

Joda-Time

The java.util.Date & Calendar classes bundled with Java are notoriously troublesome. Avoid them. Use Joda-Time or the new java.time.* package bundled with Java 8.

In JodaTime, a DateTime object truly knows its own time zone (unlike java.util.Date). Usually we use the immutable classes in Joda-Time. So instead of changing the time zone in a DateTime object, we create a fresh new DateTime object based on the old but with a specified difference. A different time zone might be that difference.

Here is some example code.

DateTimeZone timeZone_India = DateTimeZone.forID( "Asia/Kolkata" );
DateTimeZone timeZone_Ireland = DateTimeZone.forID( "Europe/Dublin" );
DateTimeZone timeZone_US_West_Coast = DateTimeZone.forID( "America/Los_Angeles" );

DateTime now = new DateTime( timeZone_India );

System.out.println( "now in India: " + now );
System.out.println( "now in Ireland: " + now.withZone( timeZone_Ireland ) );
System.out.println( "now in US West Coast: " + now.withZone( timeZone_US_West_Coast ) );
System.out.println( "now in UTC/GMT: " + now.withZone( DateTimeZone.UTC ) );

When run…

now in India: 2014-02-10T13:52:27.875+05:30
now in Ireland: 2014-02-10T08:22:27.875Z
now in US West Coast: 2014-02-10T00:22:27.875-08:00
now in UTC/GMT: 2014-02-10T08:22:27.875Z

java.time

Same idea using the java.time classes which supplant Joda-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).

Instant instant = Instant.now();

Apply a time zone.

ZoneId z = ZoneId.of( "America/Montreal" );
ZonedDateTime zdt = instant.atZone( z );

The instant and the zdt represent the same moment, the same point on the timeline. Each is seen through the lens of a different region's wall-clock time .

Generate a String by either specifying a formatting pattern or by letting java.time automatically localize.

To localize, specify:

• FormatStyle to determine how long or abbreviated should the string be.
• Locale to determine (a) the human language for translation of name of day, name of month, and such, and (b) the cultural norms deciding issues of abbreviation, capitalization, punctuation, and such.

Example:

Locale l = Locale.CANADA_FRENCH ; 
DateTimeFormatter f = DateTimeFormatter.ofLocalizedDateTime( FormatStyle.FULL ).withLocale( l );
String output = zdt.format( f );

Answer 5

Unfortunatley Java date returns time in GMT only. When ever you want display in front end or some where, you need to use the formated String generated in your step1.