move InputStream to byte-buffer conversion

- move it from Booster to XGBoost facade class

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

@@ -67,29 +67,6 @@ static Booster loadModel(String modelPath) throws XGBoostError {
     return ret;
   }
 
-  /**
-   * Load a new Booster model from a file opened as input stream.
-   * The assumption is the input stream only contains one XGBoost Model.
-   * This can be used to load existing booster models saved by other xgboost bindings.
-   *
-   * @param in The input stream of the file.
-   * @return The created boosted
-   * @throws XGBoostError
-   * @throws IOException
-   */
-  static Booster loadModel(InputStream in) throws XGBoostError, IOException {
-    int size;
-    byte[] buf = new byte[1<<20];
-    ByteArrayOutputStream os = new ByteArrayOutputStream();
-    while ((size = in.read(buf)) != -1) {
-      os.write(buf, 0, size);
-    }
-    in.close();
-    Booster ret = new Booster(new HashMap<>(), new DMatrix[0]);
-    XGBoostJNI.checkCall(XGBoostJNI.XGBoosterLoadModelFromBuffer(ret.handle,os.toByteArray()));
-    return ret;
-  }
-
   /**
    * Load a new Booster model from a byte array buffer.
    * The assumption is the array only contains one XGBoost Model.

jvm-packages/xgboost4j/src/main/java/ml/dmlc/xgboost4j/java/XGBoost.java

@@ -15,10 +15,7 @@
  */
 package ml.dmlc.xgboost4j.java;
 
-import java.io.File;
-import java.io.IOException;
-import java.io.InputStream;
-import java.io.OutputStream;
+import java.io.*;
 import java.util.*;
 
 import org.apache.commons.logging.Log;
@@ -56,9 +53,15 @@ public static Booster loadModel(String modelPath)
    * @throws XGBoostError
    * @throws IOException
    */
-  public static Booster loadModel(InputStream in)
-          throws XGBoostError, IOException {
-    return Booster.loadModel(in);
+  public static Booster loadModel(InputStream in) throws XGBoostError, IOException {
+    int size;
+    byte[] buf = new byte[1<<20];
+    ByteArrayOutputStream os = new ByteArrayOutputStream();
+    while ((size = in.read(buf)) != -1) {
+      os.write(buf, 0, size);
+    }
+    in.close();
+    return Booster.loadModel(buf);
   }
 
   /**
@@ -70,8 +73,7 @@ public static Booster loadModel(InputStream in)
    * @return The create boosted
    * @throws XGBoostError
    */
-  public static Booster loadModel(byte[] buffer)
-    throws XGBoostError, IOException {
+  public static Booster loadModel(byte[] buffer) throws XGBoostError, IOException {
     return Booster.loadModel(buffer);
   }