Serialize/deserialize maps having numerical keys. Fix spray#125

src/main/scala/spray/json/CollectionFormats.scala

@@ -17,6 +17,8 @@
 
 package spray.json
 
+import scala.util.{Try, Success, Failure}
+
 trait CollectionFormats {
 
   /**
@@ -62,6 +64,26 @@ trait CollectionFormats {
     }
   }
 
+  implicit def mapAnyValKeyFormat[K <: AnyVal : JsonFormat, V : JsonFormat] = new RootJsonFormat[Map[K, V]] {
+    def write(m: Map[K, V]) = JsObject {
+      m.map { field =>
+        field._1.toJson match {
+          case JsNumber(x) if x.isValidLong => x.toString -> field._2.toJson
+          case x => throw new SerializationException("Map key must be convertible to JsNumber, not '" + x + "'")
+        }
+      }
+    }
+    def read(value: JsValue) = value match {
+      case x: JsObject => x.fields.map { field =>
+        Try(JsNumber(BigDecimal(field._1))) match {
+          case Success(k) => (k.convertTo[K], field._2.convertTo[V])
+          case Failure(_) => deserializationError("Expected Map key to be deserializable to JsNumber, but got '" + field._1 + "'")
+        }
+      } (collection.breakOut)
+      case x => deserializationError("Expected Map as JsObject, but got " + x)
+    }
+  }
+
   import collection.{immutable => imm}
 
   implicit def immIterableFormat[T :JsonFormat]   = viaSeq[imm.Iterable[T], T](seq => imm.Iterable(seq :_*))
@@ -90,4 +112,4 @@ trait CollectionFormats {
       case x => deserializationError("Expected Collection as JsArray, but got " + x)
     }
   }
-}
+}

src/test/scala/spray/json/CollectionFormatsSpec.scala

@@ -52,8 +52,21 @@ class CollectionFormatsSpec extends Specification with DefaultJsonProtocol {
     "be able to convert a JsObject to a Map[String, Long]" in {
       json.convertTo[Map[String, Long]] mustEqual map
     }
-    "throw an Exception when trying to serialize a map whose key are not serialized to JsStrings" in {
-      Map(1 -> "a").toJson must throwA(new SerializationException("Map key must be formatted as JsString, not '1'"))
+    "convert a Map[Int, String] to a JsObject" in {
+      Map(1 -> "a").toJson mustEqual JsObject("1" -> JsString("a"))
+    }
+    "be able to convert a JsObject to a Map[Long, Int]" in {
+      val jsn = JsObject("1" -> JsNumber(1), "2" -> JsNumber(2), "3" -> JsNumber(3))
+      val mp: Map[Long, Int] = Map(1L -> 1, 2L -> 2, 3L -> 3)
+
+      jsn.convertTo[Map[Long, Int]] mustEqual Map(1L -> 1, 2L -> 2, 3L -> 3)
+      jsn.convertTo[Map[Int, Long]] mustEqual Map(1 -> 1L, 2 -> 2L, 3 -> 3L)
+    }
+    "throw an Exception when trying to deserialize a map whose key are not deserialized to JsNumber" in {
+      JsObject("a" -> JsString("1")).convertTo[Map[Int, String]] must throwA(new DeserializationException("Expected Map key to be deserializable to JsNumber, but got 'a'"))
+    }
+    "throw an Exception when trying to serialize a map whose key are not serialized to JsNumber" in {
+      Map(1.5 -> "a").toJson must throwA(new SerializationException("Map key must be convertible to JsNumber, not '1.5'"))
     }
   }
 
@@ -79,4 +92,4 @@ class CollectionFormatsSpec extends Specification with DefaultJsonProtocol {
     }
   }
 
-}
+}