[SPARK-14372][SQL] Dataset.randomSplit() needs a Java version

## What changes were proposed in this pull request?

1.Added method randomSplitAsList() in Dataset for java
for https://issues.apache.org/jira/browse/SPARK-14372

## How was this patch tested?

TestSuite

Author: Rekha Joshi <rekhajoshm@gmail.com>
Author: Joshi <rekhajoshm@gmail.com>

Closes #12184 from rekhajoshm/SPARK-14372.

sql/core/src/main/scala/org/apache/spark/sql/Dataset.scala

@@ -20,7 +20,6 @@ package org.apache.spark.sql
 import java.io.CharArrayWriter
 
 import scala.collection.JavaConverters._
-import scala.collection.mutable.ArrayBuffer
 import scala.language.implicitConversions
 import scala.reflect.runtime.universe.TypeTag
 import scala.util.control.NonFatal
@@ -1493,6 +1492,8 @@ class Dataset[T] private[sql](
    * @param weights weights for splits, will be normalized if they don't sum to 1.
    * @param seed Seed for sampling.
    *
+   * For Java API, use [[randomSplitAsList]].
+   *
    * @group typedrel
    * @since 2.0.0
    */
@@ -1510,6 +1511,20 @@ class Dataset[T] private[sql](
     }.toArray
   }
 
+  /**
+   * Returns a Java list that contains randomly split [[Dataset]] with the provided weights.
+   *
+   * @param weights weights for splits, will be normalized if they don't sum to 1.
+   * @param seed Seed for sampling.
+   *
+   * @group typedrel
+   * @since 2.0.0
+   */
+  def randomSplitAsList(weights: Array[Double], seed: Long): java.util.List[Dataset[T]] = {
+    val values = randomSplit(weights, seed)
+    java.util.Arrays.asList(values : _*)
+  }
+
   /**
    * Randomly splits this [[Dataset]] with the provided weights.
    *

sql/core/src/test/java/test/org/apache/spark/sql/JavaDatasetSuite.java

@@ -454,6 +454,16 @@ public class JavaDatasetSuite implements Serializable {
     Assert.assertEquals(data, ds.collectAsList());
   }
 
+  @Test
+  public void testRandomSplit() {
+    List<String> data = Arrays.asList("hello", "world", "from", "spark");
+    Dataset<String> ds = context.createDataset(data, Encoders.STRING());
+    double[] arraySplit = {1, 2, 3};
+
+    List<Dataset<String>> randomSplit =  ds.randomSplitAsList(arraySplit, 1);
+    Assert.assertEquals("wrong number of splits", randomSplit.size(), 3);
+  }
+
   /**
    * For testing error messages when creating an encoder on a private class. This is done
    * here since we cannot create truly private classes in Scala.