Fun with kotlin and jackson

fun_with_kotlin_and_jackson.kt

import com.fasterxml.jackson.databind.JsonNode
import com.fasterxml.jackson.databind.ObjectMapper
import com.fasterxml.jackson.module.kotlin.KotlinModule

fun main(args: Array<String>) {
    val jsonString : String = """
{
  "authors" : [
    {
      "name" : "Kalle Jönsson",
      "age" : 30
    }
  ]
}
"""

  val jsonNode = ObjectMapperSingleTon.INSTANCE.readTree(jsonString)

  // Vanilla jackson
  println(jsonNode["authors"][0]["name"].asText())
  println(jsonNode["authors"][0]["age"].asInt())

  // With our new "cast()" function where type is inferred from left hand side
  val name : String = jsonNode["authors"][0]["name"].cast()
  println(name)
  // or explicitly as a type parameter to the cast functions
  println(jsonNode["authors"][0]["age"].cast<Int>())

  // But the really cool part is that you can cast to a domain object
  // without having to have to map *everything*.
  val author : Author = jsonNode["authors"][0].cast()
  println(author.name)
  println(author.age)
}

data class Author(val name : String, val age : Int)

inline fun <reified T : Any> JsonNode.cast() : T {
  return ObjectMapperSingleTon.INSTANCE.convertValue(this, T::class.java)
}

object ObjectMapperSingleTon {
  val INSTANCE : ObjectMapper = ObjectMapper().apply {this.registerModule(KotlinModule())}
}