How to send java.util.Date in Json?

Question

I need to send data in json. What's important is that I want the locale to be preserved so that the receiver gets the date in his local time. How can I do that?

I cannot simply use Date.toString() because then I won't be able to parse it back to date on the receiving end if their locale is different(different day and month names and so on).

Is there a solution to this?

Answer 1

tl;dr

Instant.now()
       .toString()

2017-01-23T12:34:56.123456789Z

UTC

Generally best to exchange data for date-time values in UTC (GMT). Let the receiver adjust into a desired time zone.

Instant

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

Instant instant = Instant.now() ;
String output = instant.toString() ;  // Generate a String in standard ISO 8601 format.

2017-01-23T12:34:56.123456789Z

You can easily parse that string.

Instant instant = Instant.parse( "2017-01-23T12:34:56.123456789Z" ) ; 

ISO 8601

The ISO 8601 standard defines clear easy-to-read easy-to-parse formats for textual representations of date-time values. These formats are ideal for data-exchange.

For a moment in UTC, that means the format seen in example above. The T separates the date portion from the time of day portion. The Z on the end is short for Zulu and means UTC.

Locale

The Question mentions locale as if related to time zone. A Locale has nothing to do with time zone. A Locale specifies (a) the human language for translation of name of day, name of month, and such, and (b) the cultural norms deciding issues of abbreviation, capitalization, punctuation, and such.

A time zone is a history of changes to a region’s offset-from-UTC, tracking anomalies causing those changes such as Daylight Saving Time (DST).

Search Stack Overflow to learn more. This has already been covered many hundreds of times already. Search for classes such as ZoneId, ZoneOffset, ZonedDateTime, Instant, OffsetDateTime, and DateTimeFormatter. Read the Oracle Tutorial on the java.time classes.

ZonedDateTime zdt = instant.atZone( ZoneId.of( "Pacific/Auckland" ) ) ;

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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, Java SE 11, and later - 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
  • Most 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

Use java.util.Date's getTime method for the timestamp. Once you convert it back to a date every receiver can display it using it's local time zone.

Remember that Date

represents a specific instant in time, with millisecond precision.

The toString method just formats it in a specific way:

dow mon dd hh:mm:ss zzz yyyy

Chosing to send the timestamp means you also use less bandwidth.