How to convert date time from one time zone to another time zone

Question

The records are getting saved according to time zone of US but if I want to show the same record back to user it should convert the server date time with(US Time Zone) to user's date time with user's Time Zone

Answer 1

If you type in google "Java date change timezone" or "Javascript date change timezone". You will have one of your results:

In Java (source: http://www.coderanch.com/t/417443/java/java/Convert-Date-one-timezone-another )

Date date = new Date();  

DateFormat formatter = new SimpleDateFormat("dd MMM yyyy HH:mm:ss z");  
formatter.setTimeZone(TimeZone.getTimeZone("CET"));  

// Prints the date in the CET timezone  
System.out.println(formatter.format(date));  

// Set the formatter to use a different timezone  
formatter.setTimeZone(TimeZone.getTimeZone("IST"));  

// Prints the date in the IST timezone  
System.out.println(formatter.format(date));  

Javascript (source: http://www.techrepublic.com/article/convert-the-local-time-to-another-time-zone-with-this-javascript/6016329 )

// function to calculate local time
// in a different city
// given the city's UTC offset
function calcTime(city, offset) {

    // create Date object for current location
    d = new Date();

    // convert to msec
    // add local time zone offset
    // get UTC time in msec
    utc = d.getTime() + (d.getTimezoneOffset() * 60000);

    // create new Date object for different city
    // using supplied offset
    nd = new Date(utc + (3600000*offset));

    // return time as a string
    return "The local time in " + city + " is " + nd.toLocaleString();

}

// get Bombay time
alert(calcTime('Bombay', '+5.5'));

Answer 2

java.time

The old date-time classes are poorly designed, confusing, and troublesome. Avoid them.

Use modern classes: the java.time framework built into Java 8 and later. Find back-ports for earlier Java 6 & 7 and for Android.

An Instant is a moment on the timeline in UTC.

Instant now = Instant.now();

Apply a time zone (ZoneId) to get a ZonedDateTime.

Never use the 3-4 letter zone abbreviations such as EST or IST. They are neither standardized nor unique(!). Use proper time zone names, built in a continent/region format such as Asia/Kolkata, Pacific/Auckland, America/Los_Angeles.

ZoneId zoneId_Montreal = ZoneId.of( "America/Montreal" );
ZonedDateTime zdt_Montreal = ZonedDateTime.ofInstant( instant , zoneId_Montreal );

Apply a different time zone to generate another ZonedDateTime adjusted to that time zone. Call withZoneSameInstant.

ZoneId zoneId_Paris = ZoneId.of( "Europe/Paris" ); // Or "Asia/Kolkata", etc.
ZonedDateTime zdt_Paris = zdt_Montreal.withZoneSameInstant( zoneId_Paris );

If you want to go back to UTC, ask for an Instant.

Instant instant = zdt_Paris.toInstant();