[jvm-packages] support specified feature names when getModelDump and getFeatureScore (#3733)

* [jvm-packages] support specified feature names for jvm when get ModelDump and get FeatureScore (#3725)

* typo and style fix

jvm-packages/xgboost4j/src/main/scala/ml/dmlc/xgboost4j/scala/Booster.scala

@@ -187,16 +187,42 @@ class Booster private[xgboost4j](private[xgboost4j] var booster: JBooster)
     booster.getModelDump(featureMap, withStats, format)
   }
 
+  /**
+    * Dump model as Array of string with specified feature names.
+    *
+    * @param featureNames Names of features.
+    */
+  @throws(classOf[XGBoostError])
+  def getModelDump(featureNames: Array[String]): Array[String] = {
+    booster.getModelDump(featureNames, false, "text")
+  }
+
+  def getModelDump(featureNames: Array[String], withStats: Boolean, format: String)
+    : Array[String] = {
+    booster.getModelDump(featureNames, withStats, format)
+  }
+
+
   /**
    * Get importance of each feature
    *
-   * @return featureMap  key: feature index, value: feature importance score
+   * @return featureScoreMap  key: feature index, value: feature importance score
    */
   @throws(classOf[XGBoostError])
   def getFeatureScore(featureMap: String = null): mutable.Map[String, Integer] = {
     booster.getFeatureScore(featureMap).asScala
   }
 
+  /**
+    * Get importance of each feature with specified feature names.
+    *
+    * @return featureScoreMap  key: feature name, value: feature importance score
+    */
+  @throws(classOf[XGBoostError])
+  def getFeatureScore(featureNames: Array[String]): mutable.Map[String, Integer] = {
+    booster.getFeatureScore(featureNames).asScala
+  }
+
   def getVersion: Int = booster.getVersion
 
   def toByteArray: Array[Byte] = {