add ScalaObjectDeserializerModule

src/main/scala/com/fasterxml/jackson/module/scala/deser/ScalaObjectDeserializerModule.scala

@@ -0,0 +1,31 @@
+package com.fasterxml.jackson.module.scala.deser
+
+import com.fasterxml.jackson.core.JsonParser
+import com.fasterxml.jackson.databind.deser.Deserializers
+import com.fasterxml.jackson.databind.deser.std.StdDeserializer
+import com.fasterxml.jackson.databind._
+import com.fasterxml.jackson.module.scala.JacksonModule
+import com.fasterxml.jackson.module.scala.util.ClassW
+
+import scala.languageFeature.postfixOps
+
+private class ScalaObjectDeserializer(clazz: Class[_]) extends StdDeserializer[Any](classOf[Any]) {
+  override def deserialize(p: JsonParser, ctxt: DeserializationContext): Any = {
+    clazz.getDeclaredFields.find(_.getName == "MODULE$").map(_.get(null)).getOrElse(null)
+  }
+}
+
+private object ScalaObjectDeserializerResolver extends Deserializers.Base {
+  override def findBeanDeserializer(javaType: JavaType, config: DeserializationConfig, beanDesc: BeanDescription): JsonDeserializer[_] = {
+    val clazz = javaType.getRawClass
+    if (ClassW(clazz).isScalaObject)
+      new ScalaObjectDeserializer(clazz)
+    else null
+  }
+}
+
+trait ScalaObjectDeserializerModule extends JacksonModule {
+  this += { _ addDeserializers ScalaObjectDeserializerResolver }
+}
+
+object ScalaObjectDeserializerModule extends ScalaObjectDeserializerModule

src/test/scala/com/fasterxml/jackson/module/scala/deser/CaseObjectDeserializerTest.scala

@@ -0,0 +1,52 @@
+package com.fasterxml.jackson.module.scala.deser
+
+import com.fasterxml.jackson.databind.json.JsonMapper
+import com.fasterxml.jackson.module.scala.{ClassTagExtensions, DefaultScalaModule, ScalaObjectMapper}
+import com.fasterxml.jackson.module.scala.deser.CaseObjectDeserializerTest.TestObject
+
+object CaseObjectDeserializerTest {
+  case object TestObject
+}
+
+class CaseObjectDeserializerTest extends DeserializerTest {
+  def module = DefaultScalaModule
+
+  "An ObjectMapper with DefaultScalaModule and ScalaObjectDeserializerModule" should "deserialize a case object and not create a new instance" in {
+    val mapper = JsonMapper.builder().addModule(DefaultScalaModule).addModule(ScalaObjectDeserializerModule).build()
+    val original = TestObject
+    val json = mapper.writeValueAsString(original)
+    val deserialized = mapper.readValue(json, TestObject.getClass)
+    assert(deserialized == original)
+  }
+
+  "An ObjectMapper with ClassTagExtensions and ScalaObjectDeserializerModule" should "deserialize a case object and not create a new instance" in {
+    val mapper = JsonMapper.builder()
+      .addModule(DefaultScalaModule)
+      .addModule(ScalaObjectDeserializerModule)
+      .build() :: ClassTagExtensions
+    val original = TestObject
+    val json = mapper.writeValueAsString(original)
+    val deserialized = mapper.readValue[TestObject.type](json)
+    assert(deserialized == original)
+  }
+
+  "An ObjectMapper with ScalaObjectMapper and ScalaObjectDeserializerModule" should "deserialize a case object and not create a new instance" in {
+    val mapper = JsonMapper.builder()
+      .addModule(DefaultScalaModule)
+      .addModule(ScalaObjectDeserializerModule)
+      .build() :: ScalaObjectMapper
+    val original = TestObject
+    val json = mapper.writeValueAsString(original)
+    val deserialized = mapper.readValue[TestObject.type](json)
+    assert(deserialized == original)
+  }
+
+  "An ObjectMapper with DefaultScalaModule but not ScalaObjectDeserializerModule" should "deserialize a case object but create a new instance" in {
+    val mapper = JsonMapper.builder().addModule(DefaultScalaModule).build()
+    val original = TestObject
+    val json = mapper.writeValueAsString(original)
+    val deserialized = mapper.readValue(json, TestObject.getClass)
+    assert(deserialized != original)
+  }
+
+}