How to get timezone from given datetime string in java?

Question

I want to take timezone from provided date and time as a string and want to convert it into local timezone datetime. My Simple date format is

"EEE yyyy-MM-dd 'at' hh:mm:ss aa zzz"

Accroding to this the date from client is coming as

Thu 2018-08-02 at 07:10:19 am PST

Now I want to take PST as timezone and convert date and time in local timezone (for eg. IST)

I am using JAVA 8.

Answer 1

tl;dr

myJavaUtilDate                     // Some `java.util.Date` object. This troublesome class is obsolete.
.toInstant()                       // Convert from terrible legacy class to modern *java.time* class. Both represent a moment in UTC, always UTC.
.atZone(                           // Adjust from `Instant` in UTC to a `ZonedDateTime` in the wall-clock time used by the people of a particular region (a time zone).
    ZoneId.of( "Asia/Kolkata" )    // Specify time zone with `Continent/Region` name, never 3-4 letter pseudo-zone.
)                                  // Returns a `ZonedDateTime` object.
.toString()                        // Generate a String in standard ISO 8601 format extended to append name of zone.

java.time

So you have a java.util.Date object in hand? Convert from that terrible old outmoded class to its modern replacement, java.time.Instant.

Instant instant = myJavaUtilDate.toInstant() ;

Apply a time zone (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 ) ;

To generate a string is standard ISO 8601 format wisely extended to append the name of the time zone in square brackets, call toString.

String output = zdt.toString() ;  // Standard ISO 8601 format, extended by appending name of zone.

For other formats, search Stack Overflow for DateTimeFormatter class. This has been discussed many many times already.

---

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.

You may exchange java.time objects directly with your database. Use a JDBC driver compliant with JDBC 4.2 or later. No need for strings, no need for java.sql.* classes.

Where to obtain the java.time classes?

• Java SE 8, Java SE 9, Java SE 10, 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 (<26), 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.

Answer 2

You can Format your date like this:

Date date = new Date();

DateFormat formatter = new SimpleDateFormat("dd MM yyyy HH:mm:ss z");
formatter.setTimeZone(TimeZone.getTimeZone("IST"));
System.out.println(formatter.format(date));