[jvm-pacakges] the first parameter in getModelDump should be featuremap path not model path (#1788)

* fix the model dump in xgboost4j example

* Modify the dump model part of scala version

* add the forgotten modelInfos

jvm-packages/xgboost4j-example/src/main/java/ml/dmlc/xgboost4j/java/example/BasicWalkThrough.java

@@ -17,6 +17,7 @@ package ml.dmlc.xgboost4j.java.example;
 
 import java.io.File;
 import java.io.IOException;
+import java.io.PrintWriter;
 import java.util.Arrays;
 import java.util.HashMap;
 
@@ -46,6 +47,18 @@ public class BasicWalkThrough {
     return true;
   }
 
+  public static void saveDumpModel(String modelPath, String[] modelInfos) throws IOException {
+    try{
+      PrintWriter writer = new PrintWriter(modelPath, "UTF-8");
+      for(int i = 0; i < modelInfos.length; ++ i) {
+        writer.print("booster[" + i + "]:\n");
+        writer.print(modelInfos[i]);
+      }
+      writer.close();
+    } catch (Exception e) {
+      e.printStackTrace();
+    }
+  }
 
   public static void main(String[] args) throws IOException, XGBoostError {
     // load file from text file, also binary buffer generated by xgboost4j
@@ -81,11 +94,9 @@ public class BasicWalkThrough {
     String modelPath = "./model/xgb.model";
     booster.saveModel(modelPath);
 
-    //dump model
-    booster.getModelDump("./model/dump.raw.txt", false);
-
     //dump model with feature map
-    booster.getModelDump("../../demo/data/featmap.txt", false);
+    String[] modelInfos = booster.getModelDump("../../demo/data/featmap.txt", false);
+    saveDumpModel("./model/dump.raw.txt", modelInfos);
 
     //save dmatrix into binary buffer
     testMat.saveBinary("./model/dtest.buffer");

jvm-packages/xgboost4j-example/src/main/scala/ml/dmlc/xgboost4j/scala/example/BasicWalkThrough.scala

@@ -17,6 +17,7 @@
 package ml.dmlc.xgboost4j.scala.example
 
 import java.io.File
+import java.io.PrintWriter
 
 import scala.collection.mutable
 
@@ -25,6 +26,15 @@ import ml.dmlc.xgboost4j.java.example.util.DataLoader
 import ml.dmlc.xgboost4j.scala.{XGBoost, DMatrix}
 
 object BasicWalkThrough {
+  def saveDumpModel(modelPath: String, modelInfos: Array[String]): Unit = {
+    val writer = new PrintWriter(modelPath, "UTF-8")
+    for (i <- 0 until modelInfos.length) {
+      writer.print(s"booster[$i]:\n")
+      writer.print(modelInfos(i))
+    }
+    writer.close()
+  }
+
   def main(args: Array[String]): Unit = {
     val trainMax = new DMatrix("../../demo/data/agaricus.txt.train")
     val testMax = new DMatrix("../../demo/data/agaricus.txt.test")
@@ -50,10 +60,9 @@ object BasicWalkThrough {
       file.mkdirs()
     }
     booster.saveModel(file.getAbsolutePath + "/xgb.model")
-    // dump model
-    booster.getModelDump(file.getAbsolutePath + "/dump.raw.txt", false)
     // dump model with feature map
-    booster.getModelDump(file.getAbsolutePath + "/featmap.txt", false)
+    val modelInfos = booster.getModelDump(file.getAbsolutePath + "/featmap.txt", false)
+    saveDumpModel(file.getAbsolutePath + "/dump.raw.txt", modelInfos)
     // save dmatrix into binary buffer
     testMax.saveBinary(file.getAbsolutePath + "/dtest.buffer")