added javadoc and export model type in case there is a need to support

other types of export (not just PMML)

mllib/src/main/scala/org/apache/spark/mllib/export/ModelExport.scala

@@ -21,6 +21,9 @@ import java.io.OutputStream
 
 trait ModelExport {
 
+  /**
+  * Write the exported model to the output stream specified 
+  */
   def save(outputStream: OutputStream): Unit
 
 }

mllib/src/main/scala/org/apache/spark/mllib/export/ModelExportFactory.scala

@@ -19,14 +19,22 @@ package org.apache.spark.mllib.export
 
 import org.apache.spark.mllib.clustering.KMeansModel
 import org.apache.spark.mllib.export.pmml.KMeansPMMLModelExport
+import org.apache.spark.mllib.export.ModelExportType._
 
 object ModelExportFactory {
 
-  //TODO: introduce model export typed
-
-  def createModelExport(model: Any): ModelExport = model match {
-    case kmeans: KMeansModel => new KMeansPMMLModelExport
-    case _ => throw new IllegalArgumentException("Export not supported for model " + model.getClass)
+  /**
+   * Factory object to help creating the necessary ModelExport implementation 
+   * taking as input the ModelExportType (for example PMML) and the machine learning model (for example KMeansModel).
+   */
+  def createModelExport(model: Any, exportType: ModelExportType): ModelExport = {
+	 return exportType match{
+	   case PMML => model match{
+	   		case kmeans: KMeansModel => new KMeansPMMLModelExport(kmeans)
+	   		case _ => throw new IllegalArgumentException("Export not supported for model: " + model.getClass)
+	   }
+	   case _ => throw new IllegalArgumentException("Export type not supported:" + exportType)
+	 }
   }
 
 }

mllib/src/main/scala/org/apache/spark/mllib/export/ModelExportType.scala

@@ -17,6 +17,10 @@
 
 package org.apache.spark.mllib.export
 
+/**
+ * Defines export types.
+ *  - PMML exports the machine learning models in an XML-based file format called Predictive Model Markup Language developed by the Data Mining Group (www.dmg.org).
+ */
 object ModelExportType extends Enumeration{
 
   type ModelExportType = Value

mllib/src/main/scala/org/apache/spark/mllib/export/pmml/KMeansPMMLModelExport.scala

@@ -17,11 +17,19 @@
 
 package org.apache.spark.mllib.export.pmml
 
-class KMeansPMMLModelExport extends PMMLModelExport{
+import org.apache.spark.mllib.clustering.KMeansModel
 
-  populateKMeansPMML();
+/**
+ * PMML Model Export for KMeansModel class
+ */
+class KMeansPMMLModelExport(model : KMeansModel) extends PMMLModelExport{
+
+  /**
+   * Export the input KMeansModel model to PMML format
+   */
+  populateKMeansPMML(model);
 
-   def populateKMeansPMML(): Unit = {
+  private def populateKMeansPMML(model : KMeansModel): Unit = {
      //TODO: set here header description 
      pmml.setVersion("testing... kmeans..."); 
      //TODO: generate the model...

mllib/src/main/scala/org/apache/spark/mllib/export/pmml/PMMLModelExport.scala

@@ -26,10 +26,17 @@ import scala.beans.BeanProperty
 
 trait PMMLModelExport extends ModelExport{
 
+  /**
+   * Holder of the exported model in PMML format
+   */
   @BeanProperty
   var pmml: PMML = new PMML();
   //TODO: set here header app copyright and timestamp
 
+  /**
+   * Write the exported model (in PMML XML) to the output stream specified 
+   */
+  @Override
   def save(outputStream: OutputStream): Unit = {
     JAXBUtil.marshalPMML(pmml, new StreamResult(outputStream));  
   }