```@JsonFormat(pattern = "yyyy-MM-dd HH:mm", shape...

# http4k

[King River Lee]

@JsonFormat(pattern = "yyyy-MM-dd HH:mm", shape = JsonFormat.Shape.STRING)

not work on LocalDateTime field of data class

[dave]

For this, the problem is that the standard http4k mapping overrides any Jackson mapping for the type. I've not really used many of the annotations (so can't really help with the specifics of getting it working with them), but one way to fix this without annotations is to define your own marshaller:

data class FooBar(val field: LocalDateTime)

object MyJackson : ConfigurableJackson(
    KotlinModule.Builder().build()
        .asConfigurable()
        .withStandardMappings()
        .text(StringBiDiMappings.localDateTime(DateTimeFormatter.ofPattern( "yyyy-MM-dd HH:mm")))
        .done()
)

fun main() {
    println(MyJackson.asFormatString(FooBar(LocalDateTime.now())))
}

.. which will yield what you want:

{
  "field": "2023-12-06 10:36"
}

[King River Lee]

Ok. but I just use the special format in one handler. and others use default is ok.

[King River Lee]

I also disable the

WRITE_DATES_AS_TIMESTAMPS

for jackson mapper.

[dave]

you can do that in the construction of your Jackson as well.

object MyJackson : ConfigurableJackson(
    KotlinModule.Builder().build()
        .asConfigurable()
        .withStandardMappings()
        .text(StringBiDiMappings.localDateTime(DateTimeFormatter.ofPattern( "yyyy-MM-dd HH:mm")))
        .done()
        .configure(DeserializationFeature.WHATEVERFEATUREYOUWANT, true)
)

There are a few things going on here. http4k is overriding the serialization of the annotation with it's own mapping (which is in .withStandardMappings() . I don't know about the predecence of the custom mappings to the annotations for Jackson - it's all quite magical (which is why we don't try to use them). You could create a custom type which controls the serialisation

import com.fasterxml.jackson.databind.DeserializationFeature
import com.fasterxml.jackson.module.kotlin.KotlinModule
import dev.forkhandles.values.LocalDateTimeValue
import dev.forkhandles.values.LocalDateTimeValueFactory
import org.http4k.format.ConfigurableJackson
import org.http4k.format.asConfigurable
import org.http4k.format.value
import org.http4k.format.withStandardMappings
import org.http4k.lens.StringBiDiMappings
import java.time.LocalDateTime
import java.time.format.DateTimeFormatter

class MyFunnyDateTime private constructor(value: LocalDateTime) : LocalDateTimeValue(value) {
    companion object : LocalDateTimeValueFactory<MyFunnyDateTime>(
        ::MyFunnyDateTime, fmt =
        DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm")
    )
}

data class FooBar(val field: MyFunnyDateTime)

object MyJackson : ConfigurableJackson(
    KotlinModule.Builder().build()
        .asConfigurable()
        .withStandardMappings()
        .value(MyFunnyDateTime)
        .text(StringBiDiMappings.localDateTime(DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm")))
        .done()
        .configure(DeserializationFeature.FAIL_ON_INVALID_SUBTYPE, true)
)

fun main() {
    println(MyJackson.asFormatString(FooBar(MyFunnyDateTime.of(LocalDateTime.now()))))
}

[King River Lee]

Yes, annotation is magic. So I will try your method. I will try less annotation in the furture. Thanks