15.2. Creating a JSON String from Classes That Have Collections

Problem

You want to generate a JSON representation of a Scala object that contains one or more collections, such as a Person class that has a list of friends or addresses.

Solution

Once classes start containing collections, converting them to JSON becomes more difficult. In this situation, I prefer to use the Lift-JSON domain-specific library (DSL) to generate the JSON.

Lift-JSON version 1

The Lift-JSON library uses its own DSL for generating JSON output from Scala objects. As shown in the previous recipe, this isn’t necessary for simple objects, but it is necessary once objects become more complex, specifically once they contain collections. The benefit of this approach is that you have complete control over the JSON that is generated.

The following example shows how to generate a JSON string for a Person class that has a friends field defined as List[Person]:

import net.liftweb.json._
import net.liftweb.json.JsonDSL._

case class Person(name: String, address: Address) {
  var friends = List[Person]()
}

case class Address(city: String, state: String)

object LiftJsonListsVersion1 extends App {

  //import net.liftweb.json.JsonParser._
  implicit val formats = DefaultFormats

  val merc = Person("Mercedes", Address("Somewhere", "KY"))
  val mel = Person("Mel", Address("Lake Zurich", "IL"))
  val friends = List(merc, mel)
  val p = Person("Alvin Alexander", Address("Talkeetna", "AK"))
  p.friends = friends

  // define the json output
  val json 

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