[JVM] Make JVM Serializable

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

@@ -1,9 +1,10 @@
 package ml.dmlc.xgboost4j;
 
 import java.io.IOException;
+import java.io.Serializable;
 import java.util.Map;
 
-public interface Booster {
+public interface Booster extends Serializable {
 
   /**
    * set parameter
@@ -109,12 +110,25 @@ public interface Booster {
   float[][] predict(DMatrix data, int treeLimit, boolean predLeaf) throws XGBoostError;
 
   /**
-   * save model to modelPath
-   *
+   * save model to modelPath, the model path support depends on the path support
+   * in libxgboost. For example, if we want to save to hdfs, libxgboost need to be
+   * compiled with HDFS support.
+   * See also toByteArray
    * @param modelPath model path
    */
   void saveModel(String modelPath) throws XGBoostError;
 
+  /**
+   * Save the model as byte array representation.
+   * Write these bytes to a file will give compatible format with other xgboost bindings.
+   *
+   * If java natively support HDFS file API, use toByteArray and write the ByteArray,
+   *
+   * @return the saved byte array.
+   * @throws XGBoostError
+   */
+  byte[] toByteArray() throws XGBoostError;
+
   /**
    * Dump model into a text file.
    *

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

@@ -57,7 +57,6 @@ class JavaBoosterImpl implements Booster {
     setParams(params);
   }
 
-
   /**
    * load model from modelPath
    *
@@ -440,6 +439,22 @@ class JavaBoosterImpl implements Booster {
     return featureScore;
   }
 
+  /**
+   * Save the model as byte array representation.
+   * Write these bytes to a file will give compatible format with other xgboost bindings.
+   *
+   * If java natively support HDFS file API, use toByteArray and write the ByteArray,
+   *
+   * @return the saved byte array.
+   * @throws XGBoostError
+   */
+  public byte[] toByteArray() throws XGBoostError {
+    byte[][] bytes = new byte[1][];
+    JNIErrorHandle.checkCall(XgboostJNI.XGBoosterGetModelRaw(this.handle, bytes));
+    return bytes[0];
+  }
+
+
   /**
    * Load the booster model from thread-local rabit checkpoint.
    * This is only used in distributed training.
@@ -475,6 +490,27 @@ class JavaBoosterImpl implements Booster {
     return handles;
   }
 
+  // making Booster serializable
+  private void writeObject(java.io.ObjectOutputStream out)
+          throws IOException {
+    try {
+      out.writeObject(this.toByteArray());
+    } catch (XGBoostError ex) {
+      throw new IOException(ex.toString());
+    }
+  }
+
+  private void readObject(java.io.ObjectInputStream in)
+          throws IOException, ClassNotFoundException {
+    try {
+      this.init(null);
+      byte[] bytes = (byte[])in.readObject();
+      JNIErrorHandle.checkCall(XgboostJNI.XGBoosterLoadModelFromBuffer(this.handle, bytes));
+    } catch (XGBoostError ex) {
+      throw new IOException(ex.toString());
+    }
+  }
+
   @Override
   protected void finalize() throws Throwable {
     super.finalize();

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

@@ -23,7 +23,7 @@ import scala.collection.mutable
 import ml.dmlc.xgboost4j.XGBoostError
 
 
-trait Booster {
+trait Booster extends Serializable {
 
 
   /**

src/common/common.cc

@@ -19,5 +19,5 @@ typedef ThreadLocalStore<RandomThreadLocalEntry> RandomThreadLocalStore;
 GlobalRandomEngine& GlobalRandom() {
   return RandomThreadLocalStore::Get()->engine;
 }
-}
+}  // namespace common
 }  // namespace xgboost