CODEWITHSUNDEEP
javakotlin
saiedmomen
saiedmomen

Reputation: 1431

LocalDate epochDay format is one day off

I'm trying to convert date string to epoch Day using Java8's LocalDate api. When I try to verify the conversion it is actually one day off!

Here is the test

const val DATE_PATTERN = "MMMM d, yyyy"
    @Test
    fun `parse handles different cases`(){
        val case1 = "September 31, 2018"
        val dateTimeFormatter = DateTimeFormatter.ofPattern(DATE_PATTERN, Locale("en", "US"))
        val date1: Long = LocalDate.parse(case1, dateTimeFormatter).toEpochDay()
        val case1Res = LocalDate.ofEpochDay(date1).format(dateTimeFormatter)
        assertEquals(case1, case1Res)
     }

The assertion fails with

expected: <September 31, 2018> but was: <September 30, 2018>

Upvotes: 0

Views: 648

Answers (1)

Rolf
Rolf

Reputation: 7288

The comments state that, indeed, there are 30 days in September. The reason this code does not raise an error when parsing an incorrect date is because the DateFormatter is lenient by default, meaning that you can pass in September 64, 2018 and it will happily parse it for you and produce a correct epoch date.

You can make the DateFormatter throw an error on incorrect dates by adding a strict resolver style, like so:

DateTimeFormatter
    .ofPattern(DATE_PATTERN, Locale("en", "US"))
    .withResolverStyle(ResolverStyle.STRICT)

This will result in the following error when parsing the specified date:

Text 'September 31, 2018' could not be parsed: Unable to obtain LocalDate from TemporalAccessor: {YearOfEra=2018, MonthOfYear=9, DayOfMonth=31},ISO of type java.time.format.Parsed

Upvotes: 3

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