Date time String + TimeZone

Question

I have a String representation of a local date time, and a Java TimeZone.

I am trying to get output in the format MM/dd/yyyy HH:mm:ssZ but I can't figure out how to create a Calendar or JodaTime object with the correct date time and timezone. How do you get a TimeZone converted to a value that can be parsed by SimpleDateFormat 'Z' or 'z'?

TimeZone tz = TimeZone.getTimeZone("America/Chicago");
String startDate = "08/14/2014 15:00:00";

SimpleDateFormat sdf = new SimpleDateFormat("MM/dd/yyyy HH:mm:ss");
Calendar cal = Calendar.getInstance(tz);
cal.setTime(sdf.parse(startDate));
SimpleDateFormat sdf = new SimpleDateFormat("MM/dd/yyyy HH:mm:ssZ");

and

sdfZ.format(cal.getTime())

returns

08/14/2014 15:00:00-0400

which is EST.

Is the only workaround to create a Calendar or Joda DateTime and set the individual year/month/day/hour/min values by parsing the string "08/14/2014 15:00:00" ?

In the example above I am trying to get '08/14/2014 15:00:00-0500' which represents the date time '08/14/2014 15:00:00' in CST. — Shawn, Aug 29 '14 at 14:19
FYI, the troublesome old date-time classes such as [`java.util.Date`](https://docs.oracle.com/javase/9/docs/api/java/util/Date.html), [`java.util.Calendar`](https://docs.oracle.com/javase/9/docs/api/java/util/Calendar.html), and `java.text.SimpleDateFormat` are now [legacy](https://en.wikipedia.org/wiki/Legacy_system), supplanted by the [java.time](https://docs.oracle.com/javase/9/docs/api/java/time/package-summary.html) classes built into Java 8 & Java 9. See [Tutorial by Oracle](https://docs.oracle.com/javase/tutorial/datetime/TOC.html). — Basil Bourque, Feb 12 '18 at 22:53

Tkachuk_Evgen · Accepted Answer · 2014-08-28T22:20:56.733

1

Calendar getTime() - Returns a Date object representing this Calendar's time value (millisecond offset from the Epoch(01-01-1970 00:00 GMT)") irrespective of which timezone you are displaying. But hour of day in different TimeZone will be different. get(Calendar.HOUR_OF_DAY)

You should try

sdfZ.setTimeZone(tz);

edited Aug 28 '14 at 22:20

answered Aug 28 '14 at 22:09

Tkachuk_Evgen

1,334
11
17

Thanks. Setting the timezone of the SimpleDateFormat before the cal.setTime(sdf.parse(startDate)) did the trick. – Shawn Aug 29 '14 at 14:21

Basil Bourque · Answer 2 · 2018-02-12T22:54:21.270

tl;dr

ZonedDateTime zdt = ZonedDateTime.now( ZoneId.of( "America/Chicago" ) ) ;
String output = zdt.toInstant().toString() ;

2016-12-03T10:15:30Z

java.time

Both the java.util.Calendar class and the Joda-Time library have been supplanted by the java.time classes.

`Instant`

The Instant class represents a moment on the timeline in UTC with a resolution of nanoseconds.

Instant instant = Instant.now();

Call toString to generate a String in standard ISO 8601 format. For example, 2011-12-03T10:15:30Z. This format is good for serializing date-time values for data storage or exchange.

String output = instant.toString();  // Ex: 2011-12-03T10:15:30Z

Time zone

Assign a time zone.

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

As a shortcut, you can skip over using Instant.

ZonedDateTime zdt = ZonedDateTime.now( z );

Calling toString on ZonedDateTime gets you an extended version of standard ISO 8601 format where the name of the time zone is appended in square brackets. For example, 2007-12-03T10:15:30+01:00[Europe/Paris].

String output = zdt.toString(); //  Ex: 2007-12-03T10:15:30+01:00[Europe/Paris]

`DateTimeFormatter`

The DateTimeFormatter class has a predefined formatter constant for your desired output: DateTimeFormatter.ISO_LOCAL_DATE_TIME

String output zdt.format( DateTimeFormatter.ISO_LOCAL_DATE_TIME );

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.

With a JDBC driver complying with JDBC 4.2 or later, you may exchange java.time objects directly with your database. No need for strings or java.sql.* classes.

Where to obtain the java.time classes?

Java SE 8, Java SE 9, 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, 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.