make java return values immutable

Author: tgravescs

core/src/main/scala/org/apache/spark/resource/ExecutorResourceRequests.scala

@@ -39,7 +39,7 @@ private[spark] class ExecutorResourceRequests() extends Serializable {
 
   def requests: Map[String, ExecutorResourceRequest] = _executorResources.asScala.toMap
 
-  def requestsJMap: JMap[String, ExecutorResourceRequest] = _executorResources.asScala.asJava
+  def requestsJMap: JMap[String, ExecutorResourceRequest] = _executorResources.asScala.toMap.asJava
 
   /**
    * Specify heap memory. The value specified will be converted to MiB.

core/src/main/scala/org/apache/spark/resource/TaskResourceRequests.scala

@@ -38,7 +38,7 @@ private[spark] class TaskResourceRequests() extends Serializable {
 
   def requests: Map[String, TaskResourceRequest] = _taskResources.asScala.toMap
 
-  def requestsJMap: JMap[String, TaskResourceRequest] = _taskResources.asScala.asJava
+  def requestsJMap: JMap[String, TaskResourceRequest] = _taskResources.asScala.toMap.asJava
 
   /**
    * Specify number of cpus per Task.