How to parse different date strings to LocalDate/Year?

Question

I get list of objects from Json, each of them includes date String. There are two different formats, one is standard "yyyy-MM-dd" format, second is just year "yyyy". What is the elegant way to parse these string to unix timestamp? At the moment i am using double try-catch block with SimpleDateFormat but i would like to find better solution.

You can look into this solution https://stackoverflow.com/questions/4024544/how-to-parse-dates-in-multiple-formats-using-simpledateformat — Shivam Pandey, Jun 13 '19 at 05:36
You can really think of considering solution of @MạnhQuyếtNguyễn. However, you can also check if string length is 4 then you need to parse the date else you can use standard format. — Aniket Kulkarni, Jun 13 '19 at 05:46
How can you figure out a unix timestamp just from a year? Do you just want to get the time at 1 Jan 00:00 of that year? — Sweeper, Jun 13 '19 at 05:50
@Sweeper I assume they expect me to do exactly what you said, get the time at 1 Jan 00:00. — someone_smarter, Jun 13 '19 at 05:54
*get the time at 1 Jan 00:00* You will need to decide on a time zone for that too. — Ole V.V., Jun 13 '19 at 13:44

Basil Bourque · Answer 1 · 2019-06-13T06:13:43.813

If the length is four characters long, parse as a Year.

Year y = Year.parse( input ) ;

How do you want to represent that as a moment? Perhaps first moment of first day of the year, in UTC?

LocalDate ld = y.atDay( 1 ) ;
Instant instant = ld.atStartOfDay( ZoneOffset.UTC ).toInstant() ;

By “Unix timestamp” did you mean a count of milliseconds since the first moment of 1970 in UTC?

long millis = instant.toEpochMilli() ;

If the input is 10 characters long, parse as a LocalDate.

LocalDate ld = LocalDate.parse( input ) ;

The do the same as seen above.

long millis = ld.atStartOfDay( ZoneOffset.UTC ).toInstant().toEpochMilli() ;

Put that all together.

switch ( input.length() ) {
    case 4 : return Year.parse( input ).atDay( 1 ).atStartOfDay( ZoneOffset.UTC ).toInstant().toEpochMilli() ;
    case 10 : return LocalDate.parse( input ).atStartOfDay( ZoneOffset.UTC ).toInstant().toEpochMilli() ;
    default : … throw exception, unexpected input. 
}

How to parse different date strings to LocalDate/Year?

1 Answers1