使用gson库将Scala Seq对象转换为JSON

Question

I am trying to do the following:

`import com.google.gson.Gson

 object someObject extends App{
      case class entries(a:Seq[String], b:String){
         def toJson() = new Gson().toJson(this)
      }

      val one : Seq[String] = List("m","n")
      val two : String = "ok"

      val ans = entries(a = one, b = two)
      println(ans.toJson)
 }`

I am getting the following output:

 `{"a":{},"b":"ok"}`

Can i know why i am not able to convert the seq to json? I tried other libraries including spray.json and json4s but no help. Tried a lot over this.

Any help is appreciated. Other similar answers did not help.

Answer 1

Since Gson library is a Java library, I would try to use Java collections instead of Scala collections. With java.util.List instead of scala.collections.Seq and java.util.ArrayList instead of scala List you should get the right output:

import com.google.gson.Gson
import scala.collection.JavaConversions._
import java.util.ArrayList
import java.util.List

object someObject extends App {

  case class entries(a: List[String], b: String) {
    def toJson() = new Gson().toJson(this)
  }

  val one: List[String] = new ArrayList[String]
  one.add("m")
  one.add("n")
  val two: String = "ok"

  val ans = entries(a = one, b = two)
  println(ans.toJson)
}

Output now is:

{"a":["m","n"],"b":"ok"}

Answer 2

You can try

case class Entry(a:Array[String], b:String)
val e = Entry(Array("a", "b"), "c")
val gson = new Gson
println(gson.toJson(e))

gson can parse Array type the output will be: {"a":["a","b"],"b":"c"}

Answer 3

Try jsoniter-scala , it supports all Scala collections, also it is most efficient serializer to JSON for Scala. Here are results of benchmarks which compare parsing & serialization performance of this library vs. Jackson, Circe and Play-JSON libraries using JDK 8.

Add the library to your dependencies list

libraryDependencies ++= Seq(
  "com.github.plokhotnyuk.jsoniter-scala" %% "jsoniter-scala-core" % "0.29.2" % Compile, 
  "com.github.plokhotnyuk.jsoniter-scala" %% "jsoniter-scala-macros" % "0.29.2" % Provided // required only in compile-time
)

Generate codecs for your case classes, collections, etc.

import com.github.plokhotnyuk.jsoniter_scala.macros._
import com.github.plokhotnyuk.jsoniter_scala.core._

case class entries(a: Seq[String], b: String)

implicit val codec: JsonValueCodec[entries] = JsonCodecMaker.make[entries](CodecMakerConfig())

Now you can use it for serialization

writeToArray(entries(a = Seq("m", "n"), b = "ok"))