Timezone conversion

Question

I need to convert from one timezone to another timezone in my project.

I am able to convert from my current timezone to another but not from a different timezone to

Answer 1

If you don't want to use Joda, here is a deterministic way using the built in libraries.

First off I recommend that you force your JVM to default to a timezone. This addresses the issues you might run into as you move your JVM from one machine to another that are set to different timezones but your source data is always a particular timezone. For example, lets say your data is always PDT/PST time zone, but you run on a box that is set to UTC timezone.

The following code snippet sets the default timezone in my JVM:

 //You can either pass the JVM a parameter that 
 //enforces a TZ: java -Duser.timezone=UTC or you can do it
 //programatically like this
 TimeZone tz = TimeZone.getTimeZone("America/Los_Angeles");
 TimeZone.setDefault(tz);

Now lets say your source date is coming in as PDT/PST but you need to convert it to UTC. These are the steps:

    DateFormat dateFormatUtc = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
    DateFormat dateFormat = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
    dateFormatUtc.setTimeZone(TimeZone.getTimeZone("UTC"));

    String dateStrInPDT = "2016-05-19 10:00:00";
    Date dateInPDT = dateFormat.parse(dateStrInPDT);


    String dateInUtc = dateFormatUtc.format(dateInPDT);

    System.out.println("Date In UTC is " + dateInUtc);

The output would be:

Date In UTC is 2016-05-19 17:00:00