Added method for sorted print

This method prints in the same format
as PrettyPrinter but sorts the keys
of each object lexicographically.

The impetus for this change was this
question:
http://stackoverflow.com/questions/31418626/sort-fields-in-rendered-json

In general it is useful to be able to have more deterministic
control over the ordering of output, if diff tools
are to be used.

4 files changed, 63 insertions, 1 deletions

diff --git a/src/main/scala/spray/json/JsValue.scala b/src/main/scala/spray/json/JsValue.scala
index b21672d..a269475 100644
--- a/src/main/scala/spray/json/JsValue.scala
+++ b/src/main/scala/spray/json/JsValue.scala
@@ -28,6 +28,7 @@ sealed abstract class JsValue {
   def toString(printer: (JsValue => String)) = printer(this)
   def compactPrint = CompactPrinter(this)
   def prettyPrint = PrettyPrinter(this)
+  def sortedPrint = SortedPrinter(this)
   def convertTo[T :JsonReader]: T = jsonReader[T].read(this)
 
   /**
diff --git a/src/main/scala/spray/json/PrettyPrinter.scala b/src/main/scala/spray/json/PrettyPrinter.scala
index 57cf35e..6af5443 100644
--- a/src/main/scala/spray/json/PrettyPrinter.scala
+++ b/src/main/scala/spray/json/PrettyPrinter.scala
@@ -37,9 +37,11 @@ trait PrettyPrinter extends JsonPrinter {
     }
   }
 
+  protected def organiseMembers(members: Map[String, JsValue]): Seq[(String, JsValue)] = members.toSeq
+
   protected def printObject(members: Map[String, JsValue], sb: StringBuilder, indent: Int) {
     sb.append("{\n")    
-    printSeq(members, sb.append(",\n")) { m =>
+    printSeq(organiseMembers(members), sb.append(",\n")) { m =>
       printIndent(sb, indent + Indent)
       printString(m._1, sb)
       sb.append(": ")
diff --git a/src/main/scala/spray/json/SortedPrinter.scala b/src/main/scala/spray/json/SortedPrinter.scala
new file mode 100644
index 0000000..070d36c
--- /dev/null
+++ b/src/main/scala/spray/json/SortedPrinter.scala
@@ -0,0 +1,9 @@
+package spray.json
+
+trait SortedPrinter extends PrettyPrinter {
+
+  override protected def organiseMembers(members: Map[String, JsValue]): Seq[(String, JsValue)] =
+    members.toSeq.sortBy(_._1)
+}
+
+object SortedPrinter extends SortedPrinter
diff --git a/src/test/scala/spray/json/SortedPrinterSpec.scala b/src/test/scala/spray/json/SortedPrinterSpec.scala
new file mode 100644
index 0000000..0ea1045
--- /dev/null
+++ b/src/test/scala/spray/json/SortedPrinterSpec.scala
@@ -0,0 +1,50 @@
+package spray.json
+
+import scala.collection.immutable.ListMap
+import org.specs2.mutable._
+
+class SortedPrinterSpec extends Specification {
+
+  "The SortedPrinter" should {
+    "print a more complicated JsObject nicely aligned with fields sorted" in {
+      val obj = JsonParser {
+        """{
+          |  "Unic\u00f8de" :  "Long string with newline\nescape",
+          |  "Boolean no": false,
+          |  "number": -1.2323424E-5,
+          |  "key with \"quotes\"" : "string",
+          |  "key with spaces": null,
+          |  "simpleKey" : "some value",
+          |    "zero": 0,
+          |  "sub object" : {
+          |    "sub key": 26.5,
+          |    "a": "b",
+          |    "array": [1, 2, { "yes":1, "no":0 }, ["a", "b", null], false]
+          |  },
+          |  "Boolean yes":true
+          |}""".stripMargin
+      }
+      SortedPrinter(obj) mustEqual {
+        """{
+          |  "Boolean no": false,
+          |  "Boolean yes": true,
+          |  "Unic\u00f8de": "Long string with newline\nescape",
+          |  "key with \"quotes\"": "string",
+          |  "key with spaces": null,
+          |  "number": -0.000012323424,
+          |  "simpleKey": "some value",
+          |  "sub object": {
+          |    "a": "b",
+          |    "array": [1, 2, {
+          |      "no": 0,
+          |      "yes": 1
+          |    }, ["a", "b", null], false],
+          |    "sub key": 26.5
+          |  },
+          |  "zero": 0
+          |}""".stripMargin
+      }
+    }
+  }
+
+}