[jvm] Add ability to load booster direct from byte array (#6655)

* Add ability to load booster direct from byte array

* fix compiler error

* 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

@@ -62,31 +62,23 @@ public class Booster implements Serializable, KryoSerializable {
     if (modelPath == null) {
       throw new NullPointerException("modelPath : null");
     }
-    Booster ret = new Booster(new HashMap<String, Object>(), new DMatrix[0]);
+    Booster ret = new Booster(new HashMap<>(), new DMatrix[0]);
     XGBoostJNI.checkCall(XGBoostJNI.XGBoosterLoadModel(ret.handle, modelPath));
     return ret;
   }
 
   /**
-   * Load a new Booster model from a file opened as input stream.
+   * Load a new Booster model from a byte array buffer.
-   * The assumption is the input stream only contains one XGBoost Model.
+   * The assumption is the array 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.
+   * @param buffer The byte contents of the booster.
-   * @return The create boosted
+   * @return The created boosted
    * @throws XGBoostError
-   * @throws IOException
    */
-  static Booster loadModel(InputStream in) throws XGBoostError, IOException {
+  static Booster loadModel(byte[] buffer) throws XGBoostError {
-    int size;
+    Booster ret = new Booster(new HashMap<>(), new DMatrix[0]);
-    byte[] buf = new byte[1<<20];
+    XGBoostJNI.checkCall(XGBoostJNI.XGBoosterLoadModelFromBuffer(ret.handle, buffer));
-    ByteArrayOutputStream os = new ByteArrayOutputStream();
-    while ((size = in.read(buf)) != -1) {
-      os.write(buf, 0, size);
-    }
-    in.close();
-    Booster ret = new Booster(new HashMap<String, Object>(), new DMatrix[0]);
-    XGBoostJNI.checkCall(XGBoostJNI.XGBoosterLoadModelFromBuffer(ret.handle,os.toByteArray()));
     return ret;
   }
 

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.*;
-import java.io.IOException;
-import java.io.InputStream;
-import java.io.OutputStream;
 import java.util.*;
 
 import org.apache.commons.logging.Log;
@@ -56,9 +53,28 @@ public class XGBoost {
    * @throws XGBoostError
    * @throws IOException
    */
-  public static Booster loadModel(InputStream in)
+  public static Booster loadModel(InputStream in) throws XGBoostError, IOException {
-          throws XGBoostError, IOException {
+    int size;
-    return Booster.loadModel(in);
+    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);
+  }
+
+  /**
+   * Load a new Booster model from a byte array buffer.
+   * The assumption is the array only contains one XGBoost Model.
+   * This can be used to load existing booster models saved by other xgboost bindings.
+   *
+   * @param buffer The byte contents of the booster.
+   * @return The create boosted
+   * @throws XGBoostError
+   */
+  public static Booster loadModel(byte[] buffer) throws XGBoostError, IOException {
+    return Booster.loadModel(buffer);
   }
 
   /**