SCALA-400 Add code for zio-json article

Author: Matteo Di Pirro

build.sbt

@@ -640,8 +640,10 @@ lazy val zio2 = (project in file("zio-2"))
     name := "zio-2",
     scalaVersion := scala3Version,
     libraryDependencies += "dev.zio" %% "zio" % zioVersion,
+    libraryDependencies += "dev.zio" %% "zio-json" % "0.6.2",
     libraryDependencies += "dev.zio" %% "zio-test" % zioVersion % Test,
     libraryDependencies += "dev.zio" %% "zio-test-sbt" % zioVersion % Test,
+    libraryDependencies ++= scalaTestDeps,
     testFrameworks += new TestFramework("zio.test.sbt.ZTestFramework")
   )
 

zio-2/src/main/scala/com/baeldung/scala/zio/json/BaeldungZIOJson.scala

@@ -0,0 +1,27 @@
+package com.baeldung.scala.zio.json
+
+import zio.json.*
+
+sealed trait Command
+case class Start(timeout: Long) extends Command
+case object Stop extends Command
+
+@jsonDiscriminator("type")
+sealed trait Command2
+case class Start2(timeout: Long) extends Command2
+case object Stop2 extends Command2
+
+object Start {
+  implicit val encoder: JsonEncoder[Start] = DeriveJsonEncoder.gen[Start]
+  implicit val decoder: JsonDecoder[Start] = DeriveJsonDecoder.gen[Start]
+}
+
+object Command {
+  implicit val encoder: JsonEncoder[Command] = DeriveJsonEncoder.gen[Command]
+  implicit val decoder: JsonDecoder[Command] = DeriveJsonDecoder.gen[Command]
+}
+
+object Command2 {
+  implicit val encoder: JsonEncoder[Command2] = DeriveJsonEncoder.gen[Command2]
+  implicit val decoder: JsonDecoder[Command2] = DeriveJsonDecoder.gen[Command2]
+}

zio-2/src/test/scala/com/baeldung/scala/zio/json/DecodingSpec.scala

@@ -0,0 +1,53 @@
+package com.baeldung.scala.zio.json
+
+import org.scalatest.matchers.should.Matchers
+import org.scalatest.wordspec.AnyWordSpec
+import zio.json.*
+
+class DecodingSpec extends AnyWordSpec with Matchers {
+  "zio-json" should {
+    "decode a JSON object to a case class" in {
+      """{"timeout":789}""".fromJson[Start] shouldBe Right(Start(789))
+    }
+
+    "return a decoding error if the JSON is not correct" in {
+      """{"duration":789}""".fromJson[Start] shouldBe Left(".timeout(missing)")
+    }
+
+    "decode a JSON object with extra fields to a case class" in {
+      """{"timeout":789, "extra": "field"}""".fromJson[Start] shouldBe Right(
+        Start(789)
+      )
+    }
+
+    "decode an ADT to JSON" in {
+      """{"Start":{"timeout":100}}""".fromJson[Command] shouldBe Right(
+        Start(100)
+      )
+      """{"Stop":{}}""".fromJson[Command] shouldBe Right(Stop)
+    }
+
+    "decode Stop to JSON" in {
+      implicit val decoder: JsonDecoder[Stop.type] =
+        implicitly[JsonDecoder[String]].map(_ => Stop)
+
+      """{"Start":{"timeout":100}}""".fromJson[Command] shouldBe Right(
+        Start(100)
+      )
+      """"Stop"""".fromJson[Stop.type] shouldBe Right(Stop)
+    }
+
+    "use a discriminator" in {
+      """{"type":"Start2","timeout":100}""".fromJson[Command2] shouldBe Right(
+        Start2(100)
+      )
+      """{"type":"Stop2"}""".fromJson[Command2] shouldBe Right(Stop2)
+    }
+
+    "fail if there's no discriminator" in {
+      """{"timeout":100}""".fromJson[Command2] shouldBe Left(
+        "(missing hint 'type')"
+      )
+    }
+  }
+}

zio-2/src/test/scala/com/baeldung/scala/zio/json/EncodingSpec.scala

@@ -0,0 +1,33 @@
+package com.baeldung.scala.zio.json
+
+import org.scalatest.matchers.should.Matchers
+import org.scalatest.wordspec.AnyWordSpec
+import zio.json.*
+
+class EncodingSpec extends AnyWordSpec with Matchers {
+  "zio-json" should {
+    "encode a case class to JSON" in {
+      Start(100).toJson shouldBe """{"timeout":100}"""
+    }
+
+    "encode an ADT to JSON" in {
+      (Start(100): Command).toJson shouldBe """{"Start":{"timeout":100}}"""
+      (Stop: Command).toJson shouldBe """{"Stop":{}}"""
+    }
+
+    "encode Stop to JSON" in {
+      implicit val encoder: JsonEncoder[Stop.type] =
+        implicitly[JsonEncoder[String]].contramap(_.toString())
+
+      (Start(100): Command).toJson shouldBe """{"Start":{"timeout":100}}"""
+      Stop.toJson shouldBe """"Stop""""
+    }
+
+    "use a discriminator" in {
+      (Start2(
+        100
+      ): Command2).toJson shouldBe """{"type":"Start2","timeout":100}"""
+      (Stop2: Command2).toJson shouldBe """{"type":"Stop2"}"""
+    }
+  }
+}