Hi, is it possible to specify custom `Composer` f...

# serialization

[Yuri]

Hi, is it possible to specify custom Composer for Json configuration?

I need to serialize objects with spaced format like

data class Foo(val country: CountryCode)
->
{"country": "US"}

With Jackson I can specify PrettyPrinter

class SpacedPrettyPrinter : MinimalPrettyPrinter() {
    override fun writeArrayValueSeparator(g: JsonGenerator) = g.writeRaw(", ")
    override fun writeObjectFieldValueSeparator(g: JsonGenerator) = g.writeRaw(": ")
    override fun writeObjectEntrySeparator(g: JsonGenerator) = g.writeRaw(", ")
}

[Chris Lee]

what is the requirement for having a space there? it’s still valid json, the whitespace is ignored.

[Yuri]

There are only 2 options in Json configuration right now:
• prettyPrint = true - it adds \n
• prettyPrint = false - it doesn't add any spaces
In my case I need to match the format returned from JSONB columns in Postgres (using Exposed),
which adds space separators.

{
  "bar": "baz",
  "active": false,
  "balance": 7.77
}

[Chris Lee]

Not seeing where space separators are required to be there.

jsonb does not preserve white space, does not preserve the order of object keys, and does not keep duplicate object keys

Why does the format have to match, other than being valid json?

[Yuri]

Yes, they are not required and I'm not saying there is any bug here. Let's just say my business logic requires to have specific serialization format.

With Jackson it is possible with custom PrettyPrint class, I just want to know if such customization is possible with kotlin serialization:

{
  "bar": "baz",
  "active": false,
  "balance": 7.77
}

[Adam S]

aside from whether it's necessary or not, you could encode to a JsonElement

val data = SomeData(...)
val json: JsonElement = Json.encodeToJsonElement(data)

and then create an extension function to encode it to a String

fun JsonElement.toJsonBString(): String {
  return when (this) {
    is JsonObject  -> /*...*/
    is JsonArray   -> toString()
    JsonNull       -> toString()
    is JsonPrimitive -> toString()
  }
}

Everything apart from JsonObject is the same, and for JsonObject you'd have to re-implement the existing toString(), but use append(": ") instead of append(':')

[Yuri]

Got it, thanks