I am trying to serialize (and eventually deseriali...

# getting-started

[nkiesel]

I am trying to serialize (and eventually deserialize) a koltin.time.Duration property of a data class in Kotlin 1.5.30 using Jackson 2.12.5. One immediate problem is that - because Duration is a value class - Jackson sees just a long value and thus serializes a Duration.seconds(10) as 20000000000. This is obviously not what I want because it exposes the internal "use high bit to differentiate nano from milli". I tried to register a custom serializer which extends JsonSerializer<Duration>() using @JsonSerialize but that is ignored (presumably because Jackson just sees a long value). The only way I see right now is to have an explicit durationAsString property and keep that in sync with the duration property. Is there a better way? Note: I think I cannot use Kotlin serialization because this is part of a mixed Java/Kotlin project. But if I could: would that solve the issue?

[ephemient]

it could work in kotlinx.serialization, but there isn't a serializer for kotlin.time.Duration built in

[ephemient]

using Jackson's `@JsonSerialize`/`@JsonDeserialize` to customize how each field is serialized should work

[ephemient]

this also seems to work:

@ExperimentalTime
data class Foo(
    @get:JsonIgnore
    val dur: Duration
) {
    @JsonCreator constructor(
        @JsonProperty("dur")
        dur: String
    ) : this(Duration.parse(dur))
    @get:JvmName("getDur")
    val _dur: String get() = dur.toString()
}

[nkiesel]

I tried `@JsonSerialize`/`@JsonDeserialize` but could not make that work. However, the 2nd solution does work for me. Thanks a lot!

[nkiesel]

BTW: I could also make kotlinx.serialization work by creating a object DurationAsStringSerializer : KSerializer<Duration> and annotating the property with @Serializable(with = DurationAsStringSerializer::class) . This looks cleaner (and easier to replicate) than the `@JsonIgnore`/`@JsonCreator`/`@JsonProperty`/`@JvmName` approach. I will see if using kotlinx.serializatin is really not an option for my project.

[ephemient]

if it's repeated, you can use @file:Serializers(DurationAsStringSerializer::class) once at the top of the file, which is equivalent to adding @Serializable(with = ...) at every occurrence of Duration

[nkiesel]

Yeah. Ideally, the jackson-kotlin module will add custom serializers for Kotlin stdlib-specific types (and especially value/inline classes like Duration)

[ephemient]

Duration is tricky because it's an inline class, so it appears as a long with a mangled name to Java

[nkiesel]

yeah. But so are all inline/value classes. Which is why I hope we will get built-in support for these. Duration is especially tricky because it uses bit manipulation to encode type information (nanos vs. millis).

[ephemient]

https://github.com/FasterXML/jackson-module-kotlin/issues/413 all the inline stuff is effectively invisible to Java