使用密封的trait/case类玩JSON:无限递归

你需要 play-json-derived-codecs

import play.api.libs.json._
import julienrf.json.derived

sealed trait Person {
  val name: String
}

object Person {
  implicit val jsonFormat: OFormat[Person] = derived.oformat[Person]()
}

final case class Teacher(name: String, salary: Int) extends Person
final case class Student(name: String, grade: Int) extends Person


val people = List[Person] (
  Teacher("Jane Doe", 40000),
  Student("Alice", 5),
  Student("Bob", 7)
)

println(Json.prettyPrint(Json.toJson(people)))

看到这里了吗 scalafiddle

这应该做到:

import play.api.libs.json._

sealed trait Person {
  val name: String
}

final case class Teacher(name: String, salary: Int) extends Person
final case class Student(name: String, grade: Int) extends Person

implicit val teacherWrites: Writes[Teacher] = Json.writes[Teacher]
implicit val studentWrites: Writes[Student] = Json.writes[Student]

implicit val personWrites: Writes[Person] = Writes[Person] {
  case t: Teacher => Json.toJson(t)(teacherWrites)
  case s: Student => Json.toJson(s)(studentWrites)
}

val people = List[Person] (
  Teacher("Jane Doe", 40000),
  Student("Alice", 5),
  Student("Bob", 7)
)

Json.prettyPrint(Json.toJson(people))

诀窍是增加 teacherWrites 和 studentWrites 明确地。因为他们都是 Person s、 在它认出他们并给你的朋友打电话之前 personWrites 同样,堆栈溢出。