Kotlin in Action: Answers to Chapter 4 Exercises

So here are the answers to the last post:

Exercise 1: Json to Pojo and Back Again

import com.google.gson.JsonObject
import com.google.gson.JsonParser

fun main() {
  val johnJson = """{
                   |  "username": "john123",
                   |  "firstName": "John",
                   |  "lastName": "Smith",
                   |  "email": "john@smith.com"
                   |}""".trimMargin()
  val janeJson = """{
                   |  "username": "janedoe5",
                   |  "firstName": "Jane",
                   |  "lastName": "Doe",
                   |  "email": "jane.doe@gmail.com"
                   |}""".trimMargin()

  val parser = JsonParser()
  val johnJsonObject = parser.parse(johnJson).asJsonObject
  val janeJsonObject = parser.parse(janeJson).asJsonObject

  val john1 = User.fromJson(johnJsonObject)
  val john2 = User.fromJson(johnJsonObject)
  val jane = User.fromJson(janeJsonObject)

  println(john1)
  println(john2)
  println(jane)

  println("john1 = john2: " + (john1 == john2))
  println("john1 = jane: " + (john1 == jane))

  val usersSet = hashSetOf(john1, john2, jane)

  println("HashSet size (expected 2): " + usersSet.size)

  val johnFinal = john1.toJson()
  val janeFinal = jane.toJson()

  println(johnFinal)
  println(janeFinal)
}

data class User(val username: String,
                val firstName: String,
                val lastName: String,
                val email: String) {
  companion object {
    fun fromJson(jsonObject: JsonObject) : User =
      User(jsonObject.get("username").asString,
             jsonObject.get("firstName").asString,
             jsonObject.get("lastName").asString,
             jsonObject.get("email").asString)
  }

  fun toJson() : JsonObject {
    val jsonObject = JsonObject()
    jsonObject.addProperty("username", username)
    jsonObject.addProperty("firstName", firstName)
    jsonObject.addProperty("lastName", lastName)
    jsonObject.addProperty("email", email)
    return jsonObject
  }
}

Or, alternatively, if you prefer to pull the json processing out into extension functions:

import com.google.gson.JsonObject
import com.google.gson.JsonParser

fun main() {
  val johnJson = """{
                   |  "username": "john123",
                   |  "firstName": "John",
                   |  "lastName": "Smith",
                   |  "email": "john@smith.com"
                   |}""".trimMargin()
  val janeJson = """{
                   |  "username": "janedoe5",
                   |  "firstName": "Jane",
                   |  "lastName": "Doe",
                   |  "email": "jane.doe@gmail.com"
                   |}""".trimMargin()

  val parser = JsonParser()
  val johnJsonObject = parser.parse(johnJson).asJsonObject
  val janeJsonObject = parser.parse(janeJson).asJsonObject

  val john1 = User.fromJson(johnJsonObject)
  val john2 = User.fromJson(johnJsonObject)
  val jane = User.fromJson(janeJsonObject)

  println(john1)
  println(john2)
  println(jane)

  println("john1 = john2: " + (john1 == john2))
  println("john1 = jane: " + (john1 == jane))

  val usersSet = hashSetOf(john1, john2, jane)

  println("HashSet size (expected 2): " + usersSet.size)

  val johnFinal = john1.toJson()
  val janeFinal = jane.toJson()

  println(johnFinal)
  println(janeFinal)
}

data class User(val username: String,
                val firstName: String,
                val lastName: String,
                val email: String) {
  companion object
}

fun User.Companion.fromJson(jsonObject: JsonObject) : User =
  User(jsonObject.get("username").asString,
    jsonObject.get("firstName").asString,
    jsonObject.get("lastName").asString,
    jsonObject.get("email").asString)

fun User.toJson() : JsonObject {
  val jsonObject = JsonObject()
  jsonObject.addProperty("username", username)
  jsonObject.addProperty("firstName", firstName)
  jsonObject.addProperty("lastName", lastName)
  jsonObject.addProperty("email", email)
  return jsonObject
}