Json4s Examples

Json4sTest.scala

/**
 * Make sure you include the following in your build.sbt
    "org.json4s"          %% "json4s-core"       % "3.2.10",
    "org.json4s"          %% "json4s-jackson"    % "3.2.10"
 */
import org.json4s._
import org.json4s.jackson.JsonMethods._
import org.json4s.JsonDSL._

case class Candidate(name:Option[String], age:Option[Int], party:Option[String])

object JsonTest extends App{
  // Import DefaultFormats which has unmarshallers defined
  // for common data structures List, Map etc ...
  implicit val formats = DefaultFormats

  testJsonCreation()
  testJsonParsing()
  testJsonCreationWithImplicitConversion()

  def testJsonCreation(): Unit = {
    val candidates = List(
      Candidate(name = Some("Mitt Romney"), age = Some(65), party = None),
      Candidate(name = Some("Barack Obama"), age = Some(51), party = Some("Democrat"))
    )

    val jsonAst =
      (
        "candidates" -> candidates.map {
          c => ("name" -> c.name) ~ ("age" -> c.age) ~ ("party" -> c.party) }
      )

    println("--------------- testJsonCreation -------------")
    println(pretty(render(jsonAst)))
    println("----------------------------------------------")
  }

  // If you have an implicit conversion for your class instance to JValue
  // It will be used automatically to create the JSON AST
  def testJsonCreationWithImplicitConversion(): Unit = {
    implicit def candidate2JValue(c: Candidate): JValue = {
      ("name" -> c.name) ~ ("age" -> c.age) ~ ("party" -> c.party)
    }

    val candidates = List(
      Candidate(name = Some("Mitt Romney"), age = Some(65), party = None),
      Candidate(name = Some("Barack Obama"), age = Some(51), party = Some("Democrat"))
    )

    val json = ("candidates" -> candidates)

    println("--------------- testJsonCreationWithImplicitConversion -------------")
    println(pretty(render(json)))
    println("--------------------------------------------------------------------")
  }

  def testJsonParsing(): Unit = {
    val jsonString =
      """
        |{
        |  "candidates": [
        |    {
        |      "name": "Mitt Romney",
        |      "age": 65,
        |      "party": "Republican"
        |    },
        |    {
        |      "name": "Barack Obama",
        |      "age": 51,
        |      "party": "Democrat"
        |    }
        |  ]
        |}
      """.stripMargin

    val jsonAst: JValue = parse(jsonString)

    // Use XSL style querying on JSON AST
    val candidates = (jsonAst \ "candidates").extract[List[Candidate]]

    println("---------------- testJsonParsing ----------------")
    candidates foreach println
    println("-------------------------------------------------")
  }
}