Application.kt

package controllers

import com.fasterxml.jackson.databind.ObjectMapper
import com.fasterxml.jackson.databind.SerializationFeature
import com.fasterxml.jackson.datatype.jsr310.JSR310Module
import org.springframework.boot.SpringApplication
import org.springframework.boot.autoconfigure.SpringBootApplication
import org.springframework.context.annotation.Bean
import org.springframework.context.annotation.Configuration
import org.springframework.http.converter.json.MappingJackson2HttpMessageConverter
import org.springframework.web.servlet.config.annotation.WebMvcConfigurerAdapter

@SpringBootApplication
open class Application {

	companion object {
		@JvmStatic public fun main(args: Array<String>) {
			SpringApplication.run(Application::class.java, *args)
		}
	}
}

@Configuration
open class WebConfig() : WebMvcConfigurerAdapter() {
	@Bean
	open fun converter(): MappingJackson2HttpMessageConverter {
		val mapper = ObjectMapper();

		mapper.registerModule(JSR310Module());
		mapper.configure(SerializationFeature.WRITE_DATES_AS_TIMESTAMPS, false);

		return MappingJackson2HttpMessageConverter(mapper);
	}
}

EventsController.kt

package controllers

import com.fasterxml.jackson.annotation.JsonCreator
import com.fasterxml.jackson.annotation.JsonProperty
import org.springframework.web.bind.annotation.RequestBody
import org.springframework.web.bind.annotation.RequestMapping
import org.springframework.web.bind.annotation.RequestMethod
import org.springframework.web.bind.annotation.RestController

@RestController
@RequestMapping("/events")
open class EventsController {
	val events: MutableList<Event> = arrayListOf(
			Event(
					host = Host("1", "Czar"),
					activity = "playing poker",
					invited = listOf()),
			Event(
					host = Host("1", "Czar"),
					activity = "playing Dominion",
					invited = listOf()))
	/**
	give it POST `{"host":{"id":"1","name":"Czar"},"activity":"playing RPG","invited":[]}` and you'll get:
	`.c.j.MappingJackson2HttpMessageConverter : Failed to evaluate deserialization for type [simple type, class controllers.Event]: com.fasterxml.jackson.databind.JsonMappingException: Argument #0 of constructor [constructor for controllers.Guest, annotations: {interface com.fasterxml.jackson.annotation.JsonCreator=@com.fasterxml.jackson.annotation.JsonCreator()}] has no property name annotation; must have name when multiple-parameter constructor annotated as Creator`
	*/
	@RequestMapping(method = arrayOf(RequestMethod.POST), value = "")
	fun post(@RequestBody Event: Event): List<Event> {
		events.add(Event)
		return events.toList()
	}
}
data class Host @JsonCreator constructor(
		@JsonProperty("id") val id: String, @JsonProperty("name") val name: String)

data class Event @JsonCreator constructor(
		@JsonProperty("host") val host: Host,
		@JsonProperty("activity") val activity: String,
		@JsonProperty("invited") val invited: List<Guest>)

data class Guest @JsonCreator constructor(
		@JsonProperty("id") val id: String, @JsonProperty("name") val name: String,
		@JsonProperty("rsvp") var rsvp: RSVP = RSVP.interested)

enum class RSVP(val nameKey: String) {
	going("rsvp.going"), maybe("rsvp.maybe"), interested("rsvp.interested")
}