refactor scala object deserialization (#657)

* refactor scala object deserialization

* Update build.sbt

* Update Classes.scala

* refactor beanintrospector

* Update build.sbt

* Update CaseObjectDeserializerTest.scala

Update ScalaObjectDeserializerModule.scala

Author: pjfanning

src/main/scala/tools/jackson/module/scala/deser/ScalaObjectDeserializerModule.scala

@@ -12,22 +12,14 @@ import tools.jackson.module.scala.util.ClassW
 import scala.languageFeature.postfixOps
 import scala.util.control.NonFatal
 
-private class ScalaObjectDeserializer(clazz: Class[_]) extends StdDeserializer[Any](classOf[Any]) {
-  override def deserialize(p: JsonParser, ctxt: DeserializationContext): Any = {
-    try {
-      clazz.getField("MODULE$").get(null)
-    } catch {
-      case NonFatal(_) => null
-    }
-  }
+private class ScalaObjectDeserializer(value: Any) extends StdDeserializer[Any](classOf[Any]) {
+  override def deserialize(p: JsonParser, ctxt: DeserializationContext): Any = value
 }
 
 private class ScalaObjectDeserializerResolver(config: ScalaModule.Config) extends Deserializers.Base {
-  override def findBeanDeserializer(javaType: JavaType, deserializationConfig: DeserializationConfig, beanDesc: BeanDescription): ValueDeserializer[_] = {
-    val clazz = javaType.getRawClass
-    if (hasDeserializerFor(deserializationConfig, clazz))
-      new ScalaObjectDeserializer(clazz)
-    else null
+  override def findBeanDeserializer(javaType: JavaType, deserializationConfig: DeserializationConfig, beanDesc: BeanDescription): ValueDeserializer[_] = {    ClassW(javaType.getRawClass).getModuleField.flatMap { field =>
+      Option(field.get(null))
+    }.map(new ScalaObjectDeserializer(_)).orNull
   }
 
   override def hasDeserializerFor(deserializationConfig: DeserializationConfig, valueType: Class[_]): Boolean = {

src/main/scala/tools/jackson/module/scala/introspect/BeanIntrospector.scala

@@ -184,12 +184,11 @@ object BeanIntrospector {
     //create properties for all appropriate fields
     val fields = for {
       cls <- hierarchy
-      scalaCaseObject = isScalaCaseObject(cls)
-      isScalaObject = ClassW(cls).isScalaObject
       field <- cls.getDeclaredFields
+      isScalaObject = ClassW(cls).isScalaObject || isScalaCaseObject(cls)
       name = maybePrivateName(field)
       if !name.contains('$')
-      if (isScalaObject || scalaCaseObject || isAcceptableField(field))
+      if isScalaObject || isAcceptableField(field)
       beanGetter = findBeanGetter(cls, name)
       beanSetter = findBeanSetter(cls, name)
     } yield PropertyDescriptor(nameOfField(field, name), findConstructorParam(hierarchy.head, name), Some(field), findGetter(cls, name), findSetter(cls, name), beanGetter, beanSetter)

src/main/scala/tools/jackson/module/scala/util/Classes.scala

@@ -1,5 +1,6 @@
 package tools.jackson.module.scala.util
 
+import java.lang.reflect.Field
 import scala.annotation.tailrec
 import scala.language.implicitConversions
 import scala.reflect.{ScalaLongSignature, ScalaSignature}
@@ -25,9 +26,11 @@ trait ClassW extends PimpedType[Class[_]] {
     hasSigHelper(value)
   }
 
-  def isScalaObject: Boolean = {
-    Try(value.getField("MODULE$")).isSuccess
-  }
+  def isScalaObject: Boolean = moduleField.isSuccess
+
+  def getModuleField: Option[Field] = moduleField.toOption
+
+  private lazy val moduleField: Try[Field] = Try(value.getField("MODULE$"))
 }
 
 object ClassW {

src/test/scala/tools/jackson/module/scala/deser/CaseObjectDeserializerTest.scala

@@ -25,15 +25,15 @@ class CaseObjectDeserializerTest extends DeserializerTest {
     val original = TestObject
     val json = mapper.writeValueAsString(original)
     val deserialized = mapper.readValue(json, TestObject.getClass)
-    assert(deserialized == original)
+    assert(deserialized === original)
   }
 
   it should "deserialize Foo and not create a new instance" in {
     val mapper = newMapper
     val original = Foo
     val json = mapper.writeValueAsString(original)
     val deserialized = mapper.readValue(json, Foo.getClass)
-    assert(deserialized == original)
+    assert(deserialized === original)
   }
 
   it should "deserialize Foo and not create a new instance (visibility settings)" in {
@@ -47,15 +47,15 @@ class CaseObjectDeserializerTest extends DeserializerTest {
     val original = Foo
     val json = mapper.writeValueAsString(original)
     val deserialized = mapper.readValue(json, Foo.getClass)
-    assert(deserialized == original)
+    assert(deserialized === original)
   }
 
   "An ObjectMapper with ClassTagExtensions" should "deserialize a case object and not create a new instance" in {
     val mapper = newMapper :: ClassTagExtensions
     val original = TestObject
     val json = mapper.writeValueAsString(original)
     val deserialized = mapper.readValue[TestObject.type](json)
-    assert(deserialized == original)
+    assert(deserialized === original)
   }
 
   "An ObjectMapper without ScalaObjectDeserializerModule" should "deserialize a case object but create a new instance" in {