Add predefined JsonFormat for Either type

2 files changed, 44 insertions, 0 deletions

diff --git a/src/main/scala/cc/spray/json/StandardFormats.scala b/src/main/scala/cc/spray/json/StandardFormats.scala
index 2a07d6c..20012b4 100644
--- a/src/main/scala/cc/spray/json/StandardFormats.scala
+++ b/src/main/scala/cc/spray/json/StandardFormats.scala
@@ -17,12 +17,24 @@
 
 package cc.spray.json
 
+import scala.{Left, Right}
+
 /**
   * Provides the JsonFormats for the non-collection standard types.
  */
 trait StandardFormats {
 
   private type JF[T] = JsonFormat[T] // simple alias for reduced verbosity
+
+  def safeReader[A :JsonFormat] = new JsonReader[Either[Exception, A]] {
+    def read(json: JsValue) = {
+      try {
+        Right(json.fromJson)
+      } catch {
+        case e: Exception => Left(e)
+      }
+    }
+  }
   
   implicit def optionFormat[T :JF] = new JF[Option[T]] {
     def write(option: Option[T]) = option match {
@@ -34,6 +46,19 @@ trait StandardFormats {
       case x => Some(x.fromJson)
     }
   }
+
+  implicit def eitherFormat[A :JF, B :JF] = new JF[Either[A, B]] {
+    def write(either: Either[A, B]) = either match {
+      case Right(a) => a.toJson
+      case Left(b) => b.toJson
+    }
+    def read(value: JsValue) = (value.fromJson(safeReader[A]), value.fromJson(safeReader[B])) match {
+      case (Right(a), _: Left[_, _]) => Left(a)
+      case (_: Left[_, _], Right(b)) => Right(b)
+      case (_: Right[_, _], _: Right[_, _]) => throw new DeserializationException("Ambiguous Either value: can be read as both, Left and Right, values")
+      case (Left(ea), Left(eb)) => throw new DeserializationException("Could not read Either value:\n" + ea + "---------- and ----------\n" + eb)
+    }
+  }
   
   implicit def tuple1Format[A :JF] = new JF[Tuple1[A]] {
     def write(t: Tuple1[A]) = t._1.toJson
diff --git a/src/test/scala/cc/spray/json/StandardFormatsSpec.scala b/src/test/scala/cc/spray/json/StandardFormatsSpec.scala
index 00561e0..7c454ac 100644
--- a/src/test/scala/cc/spray/json/StandardFormatsSpec.scala
+++ b/src/test/scala/cc/spray/json/StandardFormatsSpec.scala
@@ -1,6 +1,7 @@
 package cc.spray.json
 
 import org.specs.Specification
+import scala.Right
 
 class StandardFormatsSpec extends Specification with StandardFormats with BasicFormats {
 
@@ -18,6 +19,24 @@ class StandardFormatsSpec extends Specification with StandardFormats with BasicF
       JsString("Hello").fromJson[Option[String]] mustEqual Some("Hello")
     } 
   }
+
+  "The eitherFormat" should {
+    val a: Either[Int, String] = Left(42)
+    val b: Either[Int, String] = Right("Hello")
+
+    "convert the left side of an Either value to Json" in {
+      a.toJson mustEqual JsNumber(42)
+    }
+    "convert the right side of an Either value to Json" in {
+      b.toJson mustEqual JsString("Hello")
+    }
+    "convert the left side of an Either value from Json" in {
+      JsNumber(42).fromJson[Either[Int, String]] mustEqual Left(42)
+    }
+    "convert the right side of an Either value from Json" in {
+      JsString("Hello").fromJson[Either[Int, String]] mustEqual Right("Hello")
+    }
+  }
   
   "The tuple1Format" should {
     "convert (42) to a JsNumber" in {