Check if 24 hours have passed (reading from a string)

Question

I am saving date\'s in a file in the following format as a string.

Sat Jul 21 23:31:55 EDT 2012

How can I check if 24 hours have passed? I am a

Answer 1

Define A Day

Do you really mean one day or 24-hours? Because of Daylight Saving Time nonsense, a day can vary in length such as 23 or 25 hours in the United States.

Avoid 3-Letter Time Zone Codes

That String format is a terrible representation of a date-time. It is difficult to parse. It uses a 3-letter time zone code, and such codes are neither standardized nor unique. If possible, choose another format. The obvious choice is ISO 8601, for example: 2014-07-08T04:17:01Z.

Use proper time zone names.

Avoid j.u.Date & .Calendar

The java.util.Date and .Calendar classes bundled with Java are notoriously troublesome. Avoid them.

Instead use either the venerable Joda-Time library or the new java.time package bundled in Java 8 (and inspired on Joda-Time).

Joda-Time

Here is some example code in Joda-Time.

Get the current moment.

DateTime now = DateTime.now();

Parse the input string.

String input = "Sat Jul 21 23:31:55 EDT 2012";
DateTime formatter = DateTimeFormat.forPattern( "EEE MMM dd HH:mm:ss zzz yyyy" ).with Locale( java.util.Locale.ENGLISH );
DateTime target = formatter.parseDateTime( input );

Calculate 24 hours (or next day).

DateTime twentyFourHoursLater = target.plusHours( 24 );

Test if current moment happened after.

boolean expired = now.isAfter( twentyFourHoursLater );

Or, if you want next day rather than 24-hours, use plusDays rather than plusHours. If necessary, adjust to desired time zone. Time zone is crucial as it defines the day/date and applies rules for anomalies such as Daylight Saving Time.

DateTime targetAdjusted = target.withZone( DateTimeZone.forID( "Europe/Paris" ) );
…
DateTime aDayLater = targetAdjusted.plusDays( 1 ); // Go to next day, accounting for DST etc.
boolean expired = now.isAfter( aDayLater ); // Test if current moment happened after.