Java SimpleDateFormat(“yyyy-MM-dd'T'HH:mm:ss'Z'”) gives timezone as IST

问题:

I have SimpleDateFormat constructor as

SimpleDateFormat("yyyy-MM-dd'T'HH:mm:ss'Z'") 

and I am parsing string "2013-09-29T18:46:19Z".

I have read that here Z represents the GMT/UTC timezone. but when I print this date on console , It prints IST timezne for the returned date.

Now my question is whether my output is right or wrong?

回答1:

You haven't set the timezone only added a Z to the end of the date/time, so it will look like a GMT date/time but this doesn't change the value.

Set the timezone to GMT and it will be correct.

SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd'T'HH:mm:ss'Z'"); sdf.setTimeZone(TimeZone.getTimeZone("GMT")); 

回答2:

'T' and 'Z' are considered here as constants. You need to pass Z without the quotes. Moreover you need to specify the timezone in the input string.

Example : 2013-09-29T18:46:19-0700 And the format as "yyyy-MM-dd'T'HH:mm:ssZ"

回答3:

IF you want to handle 'standard' JSON representation of the Date then better to use this pattern: "yyyy-MM-dd'T'HH:mm:ssX".

Notice the X on the end. It will handle timezones in ISO 8601 standard, and ISO 8601 is exactly what produces this statement in Javascript new Date().toJSON()

Comparing to other answers it has some benefits:

1. You don't need to require your clients to send date in GMT
2. You don't need to explicitly convert your Date object to GMT using this: sdf.setTimeZone(TimeZone.getTimeZone("GMT"));

回答4:

From ISO 8601 String to Java Date Object

SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd'T'HH:mm:ss'Z'"); sdf.setTimeZone(TimeZone.getTimeZone("GMT")); sdf.parse("2013-09-29T18:46:19Z"); //prints-> Mon Sep 30 02:46:19 CST 2013 

if you don't set TimeZone.getTimeZone("GMT") then it will output Sun Sep 29 18:46:19 CST 2013

From Java Date Object to ISO 8601 String

And to convert Dateobject to ISO 8601 Standard (yyyy-MM-dd'T'HH:mm:ss'Z') use following code

SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd'T'HH:mm:ss'Z'", Locale.US); sdf.setTimeZone(TimeZone.getTimeZone("GMT"));            System.out.println(sdf.format(new Date())); //-prints-> 2015-01-22T03:23:26Z 

Also note that without ' ' at Z yyyy-MM-dd'T'HH:mm:ssZ prints 2015-01-22T03:41:02+0000

回答5:

The other Answers are outmoded as of Java 8.

ISO 8601

Your string format happens to comply with the ISO 8601 standard. This standard defines sensible formats for representing various date-time values as text.

java.time

The old java.util.Date/.Calendar and java.text.SimpleDateFormat classes have been supplanted by the java.time framework built into Java 8 and later. See Tutorial. Avoid the old classes as they have proven to be poorly designed, confusing, and troublesome.

Part of the poor design in the old classes has bitten you, where the toString method applies the JVM's current default time zone when generating a text representation of the date-time value that is actually in UTC (GMT); well-intentioned but confusing.

The java.time classes use ISO 8601 formats by default when parsing/generating textual representations of date-time values. So no need to specify a parsing pattern.

An Instant is a moment on the timeline in UTC.

Instant instant = Instant.parse( "2013-09-29T18:46:19Z" ); 

You can apply a time zone as needed to produce a ZonedDateTime object.

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

回答6:

and if you don't have the option to go on java8 better use 'yyyy-MM-dd'T'HH:mm:ssXXX' as this gets correctly parsed again (while with only one X this may not be the case... depending on your parsing function)

X generates: +01

XXX generates: +01:00

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