HTTP: Document how a type is marshalled into json #20514

akka-docs/rst/scala/code/docs/http/scaladsl/SprayJsonCompactMarshalSpec.scala

@@ -0,0 +1,41 @@
+/*
+ * Copyright (C) 2009-2016 Typesafe Inc. <http://www.typesafe.com>
+ */
+package docs.http.scaladsl
+
+import akka.http.scaladsl.marshallers.sprayjson.SprayJsonSupport
+import akka.http.scaladsl.server.Directives
+import org.scalatest.{Matchers, WordSpec}
+
+class SprayJsonCompactMarshalSpec extends WordSpec with Matchers {
+
+  "spray-json example" in {
+    //#example
+    import spray.json._
+
+    // domain model
+    final case class CompactPrintedItem(name: String, id: Long)
+
+    trait CompactJsonFormatSupport extends DefaultJsonProtocol with SprayJsonSupport {
+      implicit val printer = CompactPrinter
+      implicit val compactPrintedItemFormat = jsonFormat2(CompactPrintedItem)
+    }
+
+    // use it wherever json (un)marshalling is needed
+    class MyJsonService extends Directives with CompactJsonFormatSupport{
+
+      // format: OFF
+      val route =
+        get {
+          pathSingleSlash {
+            complete {
+              // should complete with spray.json.JsValue = {"name":"akka","id":42}
+              CompactPrintedItem("akka", 42) // will render as JSON
+            }
+          }
+        }
+      // format: ON
+      //#
+    }
+  }
+}

akka-docs/rst/scala/http/common/json-support.rst

@@ -36,6 +36,13 @@ Once you have done this (un)marshalling between JSON and your type ``T`` should
 .. includecode:: ../../code/docs/http/scaladsl/SprayJsonExampleSpec.scala
   :include: example
 
+4. By default, spray-json marshals your types to pretty printed json by implicit conversion using PrettyPrinter, as defined in
+   ``implicit def sprayJsonMarshallerConverter[T](writer: RootJsonWriter[T])(implicit printer: JsonPrinter = PrettyPrinter): ToEntityMarshaller[T]``.
+   Alternately to marshal your types to compact printed json, bring a ``CompactPrinter`` in scope to perform implicit conversion.
+
+.. includecode:: ../../code/docs/http/scaladsl/SprayJsonCompactMarshalSpec.scala
+   :include: example
+
 To learn more about how spray-json works please refer to its `documentation <https://github.com/spray/spray-json>`_.