Json WithDefaultValues

import play.api.libs._
import play.api.libs.json._

scala> case class Student(name: String, surname: String, year: Int = 1, age: Int = 18)
defined class Student

scala> implicit def jsonFormat: Format[Student] = Json.using[Json.WithDefaultValues].format[Student]
jsonFormat: play.api.libs.json.Format[Student]

scala> val json = Json.parse("""{"name": "Tommy", "surname": "Gray"}""")
json: play.api.libs.json.JsValue = {"name":"Tommy","surname":"Gray"}

scala> json.asOpt[Student]
res1: Option[Student] = Some(Student(Tommy,Gray,1,18))

scala> val student = Student("John", "Brown")
student: Student = Student(John,Brown,1,18)

scala> Json.toJson(student)
res2: play.api.libs.json.JsValue = {"name":"John","surname":"Brown","year":1,"age":18}