带有 play-json 的 JSON
play-json 使用隐式格式作为其他 json 框架
SBT 依赖：libraryDependencies += ""com.typesafe.play" %% "play-json" % "2.4.8"
import play.api.libs.json._
import play.api.libs.functional.syntax._ // if you need DSL
DefaultFormat 包含读取/写入所有基本类型的默认格式。要为你自己的类型提供 JSON 功能，你可以使用便捷构建器来显示格式或写入格式。
读 json
// generates an intermediate JSON representation (abstract syntax tree)
val res = Json.parse("""{ "foo": "bar" }""") // JsValue = {"foo":"bar"}
res.as[Map[String, String]] // Map(foo -> bar)
res.validate[Map[String, String]] //JsSuccess(Map(foo -> bar),)
写 json
val values = List("a", "b", "c")
Json.stringify(Json.toJson(values)) // ["a", "b", "c"]
DSL
val json = parse("""{ "foo": [{"foo": "bar"}]}""")
(json \ "foo").get //Simple path: [{"foo":"bar"}]
(json \\ "foo") //Recursive path:List([{"foo":"bar"}], "bar")
(json \ "foo")(0).get //Index lookup (for JsArrays): {"foo":"bar"}
因为总是喜欢模式匹配 JsSuccess / JsError 并尽量避免 .get，array(i) 调用。
读写案例类
case class Address(street: String, city: String)
case class Person(name: String, address: Address)
// create the formats and provide them implicitly
implicit val addressFormat = Json.format[Address]
implicit val personFormat = Json.format[Person]
// serialize a Person
val fred = Person("Fred", Address("Awesome Street 9", "SuperCity"))
val fredJsonString = Json.stringify(Json.toJson(Json.toJson(fred)))
val personRead = Json.parse(fredJsonString).as[Person] //Person(Fred,Address(Awesome Street 9,SuperCity))
自己的格式
如果需要对类型进行特殊的序列化，可以编写自己的 JsonFormat（例如，在 scala 和 Json 中以不同的方式命名字段，或者根据输入实例化不同的具体类型）
case class Address(street: String, city: String)
// create the formats and provide them implicitly
implicit object AddressFormatCustom extends Format[Address] {
def reads(json: JsValue): JsResult[Address] = for {
street <- (json \ "Street").validate[String]
city <- (json \ "City").validate[String]
} yield Address(street, city)
def writes(x: Address): JsValue = Json.obj(
"Street" -> x.street,
"City" -> x.city
)
}
// serialize an address
val address = Address("Awesome Street 9", "SuperCity")
val addressJsonString = Json.stringify(Json.toJson(Json.toJson(address)))
//{"Street":"Awesome Street 9","City":"SuperCity"}
val addressRead = Json.parse(addressJsonString).as[Address]
//Address(Awesome Street 9,SuperCity)
替代
如果 json 与你的 case 类字段不完全匹配（案例类中的 isAlive 和 json 中的 is_alive）：
case class User(username: String, friends: Int, enemies: Int, isAlive: Boolean)
object User {
import play.api.libs.functional.syntax._
import play.api.libs.json._
implicit val userReads: Reads[User] = (
(JsPath \ "username").read[String] and
(JsPath \ "friends").read[Int] and
(JsPath \ "enemies").read[Int] and
(JsPath \ "is_alive").read[Boolean]
) (User.apply _)
}
Json 带有可选字段
case class User(username: String, friends: Int, enemies: Int, isAlive: Option[Boolean])
object User {
import play.api.libs.functional.syntax._
import play.api.libs.json._
implicit val userReads: Reads[User] = (
(JsPath \ "username").read[String] and
(JsPath \ "friends").read[Int] and
(JsPath \ "enemies").read[Int] and
(JsPath \ "is_alive").readNullable[Boolean]
) (User.apply _)
}
从 json 读取时间戳
想象一下，你有一个带有 Unix 时间戳字段的 Json 对象：
{
"field": "example field",
"date": 1459014762000
}
解：
case class JsonExampleV1(field: String, date: DateTime)
object JsonExampleV1{
implicit val r: Reads[JsonExampleV1] = (
(__ \ "field").read[String] and
(__ \ "date").read[DateTime](Reads.DefaultJodaDateReads)
)(JsonExampleV1.apply _)
}
阅读自定义案例类
现在，如果你确实包装了对象标识符以确保类型安全，那么你将会喜欢这个。请参阅以下 json 对象：
{
"id": 91,
"data": "Some data"
}
和相应的案例类：
case class MyIdentifier(id: Long)
case class JsonExampleV2(id: MyIdentifier, data: String)
现在你只需要读取原始类型（Long），并映射到你的 idenfier：
object JsonExampleV2 {
implicit val r: Reads[JsonExampleV2] = (
(__ \ "id").read[Long].map(MyIdentifier) and
(__ \ "data").read[String]
)(JsonExampleV2.apply _)
}