Scala Language JSON JSON with json4s
Example
json4s uses implicit formats as other json frameworks.
SBT dependency:
libraryDependencies += "org.json4s" %% "json4s-native" % "3.4.0"
//or
libraryDependencies += "org.json4s" %% "json4s-jackson" % "3.4.0"
Imports
import org.json4s.JsonDSL._
import org.json4s._
import org.json4s.native.JsonMethods._
implicit val formats = DefaultFormats
DefaultFormats contains default formats to read/write all basic types.
Read json
// generates an intermediate JSON representation (abstract syntax tree)
val res = parse("""{ "foo": "bar" }""") // JValue = {"foo":"bar"}
res.extract[Map[String, String]] // Map(foo -> bar)
Write json
val values = List("a", "b", "c")
compact(render(values)) // ["a", "b", "c"]
DSL
json \ "foo" //Simple path: JArray(List(JObject(List((foo,JString(bar))))))
json \\ "foo" //Recursive path: ~List([{"foo":"bar"}], "bar")
(json \ "foo")(0) //Index lookup (for JsArrays): JObject(List((foo,JString(bar))))
("foo" -> "bar") ~ ("field" -> "value") // {"foo":"bar","field":"value"}
Read and write to case class
import org.json4s.native.Serialization.{read, write}
case class Address(street: String, city: String)
val addressString = write(Address("Awesome stree", "Super city"))
// {"street":"Awesome stree","city":"Super city"}
read[Address](addressString) // Address(Awesome stree,Super city)
//or
parse(addressString).extract[Address]
Read and Write heterogenous lists
To serialize and deserialize an heterogenous (or polymorphic) list, specific type-hints need to be provided.
trait Location
case class Street(name: String) extends Location
case class City(name: String, zipcode: String) extends Location
case class Address(street: Street, city: City) extends Location
case class Locations (locations : List[Location])
implicit val formats = Serialization.formats(ShortTypeHints(List(classOf[Street], classOf[City], classOf[Address])))
val locationsString = write(Locations(Street("Lavelle Street"):: City("Super city","74658")))
read[Locations](locationsString)
Own Format
class AddressSerializer extends CustomSerializer[Address](format => (
{
case JObject(JField("Street", JString(s)) :: JField("City", JString(c)) :: Nil) =>
new Address(s, c)
},
{
case x: Address => ("Street" -> x.street) ~ ("City" -> x.city)
}
))
implicit val formats = DefaultFormats + new AddressSerializer
val str = write[Address](Address("Awesome Stree", "Super City"))
// {"Street":"Awesome Stree","City":"Super City"}
read[Address](str)
// Address(Awesome Stree,Super City)
