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javaserializationtimejacksonjackson-databind

Java/Jackson: Why serialized date has an extra 04?

When I execute the following code:

System.out.println(new ObjectMapper().configure(SerializationFeature.WRITE_DATES_AS_TIMESTAMPS, false).writeValueAsString(new SimpleDateFormat("MMMM d, yyyy", Locale.ENGLISH).parse("April 12, 2001")));

I see the output:

"2001-04-12T04:00:00.000+00:00"

I am trying to understand where the 04 after the T is coming from? My Jackson dependency:

implementation("com.fasterxml.jackson.core", "jackson-databind", "2.11.1")
Solution

  • This happens because you're not specifying time and timezone, so output contains date-time in UTC timezone. Your system has timezone UTC-4, so, 4 hours are added to the date you've provided.

    My timezone is UTC+3, so the output I'm getting

    "2001-04-11T21:00:00.000+00:00"

    I would recommend using Java 8 time for such cases, so you can always be sure what output you'll receive.

    Following code outputs

    "2001-04-12T00:00:00Z"

    regardless your local timezone.

    DateTimeFormatter formatter = DateTimeFormatter.ofPattern("MMMM d, yyyy", Locale.ENGLISH);

System.out.println(new ObjectMapper().registerModule(new JavaTimeModule()).configure(SerializationFeature.WRITE_DATES_AS_TIMESTAMPS, false).writeValueAsString(LocalDate.parse("April 12, 2001", formatter).atStartOfDay().atOffset(ZoneOffset.UTC)));

    P.S. You can play around with parsed LocalDate and it's not necessary to convert it to OffsetDateTime