[SPARK-3369] [CORE] [STREAMING] Java mapPartitions Iterator->Iterable is inconsistent with Scala's Iterator->Iterator

core/src/main/java/org/apache/spark/api/java/function/CoGroupFunction.java

@@ -25,5 +25,5 @@
  * Datasets.
  */
 public interface CoGroupFunction<K, V1, V2, R> extends Serializable {
-  Iterable<R> call(K key, Iterator<V1> left, Iterator<V2> right) throws Exception;
+  Iterator<R> call(K key, Iterator<V1> left, Iterator<V2> right) throws Exception;
 }

core/src/main/java/org/apache/spark/api/java/function/DoubleFlatMapFunction.java

@@ -18,10 +18,11 @@
 package org.apache.spark.api.java.function;
 
 import java.io.Serializable;
+import java.util.Iterator;
 
 /**
  * A function that returns zero or more records of type Double from each input record.
  */
 public interface DoubleFlatMapFunction<T> extends Serializable {
-  public Iterable<Double> call(T t) throws Exception;
+  Iterator<Double> call(T t) throws Exception;
 }

core/src/main/java/org/apache/spark/api/java/function/FlatMapFunction.java

@@ -18,10 +18,11 @@
 package org.apache.spark.api.java.function;
 
 import java.io.Serializable;
+import java.util.Iterator;
 
 /**
  * A function that returns zero or more output records from each input record.
  */
 public interface FlatMapFunction<T, R> extends Serializable {
-  Iterable<R> call(T t) throws Exception;
+  Iterator<R> call(T t) throws Exception;
 }

core/src/main/java/org/apache/spark/api/java/function/FlatMapFunction2.java

@@ -18,10 +18,11 @@
 package org.apache.spark.api.java.function;
 
 import java.io.Serializable;
+import java.util.Iterator;
 
 /**
  * A function that takes two inputs and returns zero or more output records.
  */
 public interface FlatMapFunction2<T1, T2, R> extends Serializable {
-  Iterable<R> call(T1 t1, T2 t2) throws Exception;
+  Iterator<R> call(T1 t1, T2 t2) throws Exception;
 }

core/src/main/java/org/apache/spark/api/java/function/FlatMapGroupsFunction.java

@@ -24,5 +24,5 @@
  * A function that returns zero or more output records from each grouping key and its values.
  */
 public interface FlatMapGroupsFunction<K, V, R> extends Serializable {
-  Iterable<R> call(K key, Iterator<V> values) throws Exception;
+  Iterator<R> call(K key, Iterator<V> values) throws Exception;
 }

core/src/main/java/org/apache/spark/api/java/function/MapPartitionsFunction.java

@@ -24,5 +24,5 @@
  * Base interface for function used in Dataset's mapPartitions.
  */
 public interface MapPartitionsFunction<T, U> extends Serializable {
-  Iterable<U> call(Iterator<T> input) throws Exception;
+  Iterator<U> call(Iterator<T> input) throws Exception;
 }

core/src/main/java/org/apache/spark/api/java/function/PairFlatMapFunction.java

@@ -18,6 +18,7 @@
 package org.apache.spark.api.java.function;
 
 import java.io.Serializable;
+import java.util.Iterator;
 
 import scala.Tuple2;
 
@@ -26,5 +27,5 @@
  * key-value pairs are represented as scala.Tuple2 objects.
  */
 public interface PairFlatMapFunction<T, K, V> extends Serializable {
-  public Iterable<Tuple2<K, V>> call(T t) throws Exception;
+  Iterator<Tuple2<K, V>> call(T t) throws Exception;
 }

core/src/main/scala/org/apache/spark/api/java/JavaRDDLike.scala

@@ -121,7 +121,7 @@ trait JavaRDDLike[T, This <: JavaRDDLike[T, This]] extends Serializable {
    *  RDD, and then flattening the results.
    */
   def flatMap[U](f: FlatMapFunction[T, U]): JavaRDD[U] = {
-    def fn: (T) => Iterable[U] = (x: T) => f.call(x).asScala
+    def fn: (T) => Iterator[U] = (x: T) => f.call(x).asScala
     JavaRDD.fromRDD(rdd.flatMap(fn)(fakeClassTag[U]))(fakeClassTag[U])
   }
 
@@ -130,7 +130,7 @@ trait JavaRDDLike[T, This <: JavaRDDLike[T, This]] extends Serializable {
    *  RDD, and then flattening the results.
    */
   def flatMapToDouble(f: DoubleFlatMapFunction[T]): JavaDoubleRDD = {
-    def fn: (T) => Iterable[jl.Double] = (x: T) => f.call(x).asScala
+    def fn: (T) => Iterator[jl.Double] = (x: T) => f.call(x).asScala
     new JavaDoubleRDD(rdd.flatMap(fn).map((x: jl.Double) => x.doubleValue()))
   }
 
@@ -139,7 +139,7 @@ trait JavaRDDLike[T, This <: JavaRDDLike[T, This]] extends Serializable {
    *  RDD, and then flattening the results.
    */
   def flatMapToPair[K2, V2](f: PairFlatMapFunction[T, K2, V2]): JavaPairRDD[K2, V2] = {
-    def fn: (T) => Iterable[(K2, V2)] = (x: T) => f.call(x).asScala
+    def fn: (T) => Iterator[(K2, V2)] = (x: T) => f.call(x).asScala
     def cm: ClassTag[(K2, V2)] = implicitly[ClassTag[(K2, V2)]]
     JavaPairRDD.fromRDD(rdd.flatMap(fn)(cm))(fakeClassTag[K2], fakeClassTag[V2])
   }
@@ -149,7 +149,7 @@ trait JavaRDDLike[T, This <: JavaRDDLike[T, This]] extends Serializable {
    */
   def mapPartitions[U](f: FlatMapFunction[java.util.Iterator[T], U]): JavaRDD[U] = {
     def fn: (Iterator[T]) => Iterator[U] = {
-      (x: Iterator[T]) => f.call(x.asJava).iterator().asScala
+      (x: Iterator[T]) => f.call(x.asJava).asScala
     }
     JavaRDD.fromRDD(rdd.mapPartitions(fn)(fakeClassTag[U]))(fakeClassTag[U])
   }
@@ -160,7 +160,7 @@ trait JavaRDDLike[T, This <: JavaRDDLike[T, This]] extends Serializable {
   def mapPartitions[U](f: FlatMapFunction[java.util.Iterator[T], U],
       preservesPartitioning: Boolean): JavaRDD[U] = {
     def fn: (Iterator[T]) => Iterator[U] = {
-      (x: Iterator[T]) => f.call(x.asJava).iterator().asScala
+      (x: Iterator[T]) => f.call(x.asJava).asScala
     }
     JavaRDD.fromRDD(
       rdd.mapPartitions(fn, preservesPartitioning)(fakeClassTag[U]))(fakeClassTag[U])
@@ -171,7 +171,7 @@ trait JavaRDDLike[T, This <: JavaRDDLike[T, This]] extends Serializable {
    */
   def mapPartitionsToDouble(f: DoubleFlatMapFunction[java.util.Iterator[T]]): JavaDoubleRDD = {
     def fn: (Iterator[T]) => Iterator[jl.Double] = {
-      (x: Iterator[T]) => f.call(x.asJava).iterator().asScala
+      (x: Iterator[T]) => f.call(x.asJava).asScala
     }
     new JavaDoubleRDD(rdd.mapPartitions(fn).map((x: jl.Double) => x.doubleValue()))
   }
@@ -182,7 +182,7 @@ trait JavaRDDLike[T, This <: JavaRDDLike[T, This]] extends Serializable {
   def mapPartitionsToPair[K2, V2](f: PairFlatMapFunction[java.util.Iterator[T], K2, V2]):
   JavaPairRDD[K2, V2] = {
     def fn: (Iterator[T]) => Iterator[(K2, V2)] = {
-      (x: Iterator[T]) => f.call(x.asJava).iterator().asScala
+      (x: Iterator[T]) => f.call(x.asJava).asScala
     }
     JavaPairRDD.fromRDD(rdd.mapPartitions(fn))(fakeClassTag[K2], fakeClassTag[V2])
   }
@@ -193,7 +193,7 @@ trait JavaRDDLike[T, This <: JavaRDDLike[T, This]] extends Serializable {
   def mapPartitionsToDouble(f: DoubleFlatMapFunction[java.util.Iterator[T]],
       preservesPartitioning: Boolean): JavaDoubleRDD = {
     def fn: (Iterator[T]) => Iterator[jl.Double] = {
-      (x: Iterator[T]) => f.call(x.asJava).iterator().asScala
+      (x: Iterator[T]) => f.call(x.asJava).asScala
     }
     new JavaDoubleRDD(rdd.mapPartitions(fn, preservesPartitioning)
       .map(x => x.doubleValue()))
@@ -205,7 +205,7 @@ trait JavaRDDLike[T, This <: JavaRDDLike[T, This]] extends Serializable {
   def mapPartitionsToPair[K2, V2](f: PairFlatMapFunction[java.util.Iterator[T], K2, V2],
       preservesPartitioning: Boolean): JavaPairRDD[K2, V2] = {
     def fn: (Iterator[T]) => Iterator[(K2, V2)] = {
-      (x: Iterator[T]) => f.call(x.asJava).iterator().asScala
+      (x: Iterator[T]) => f.call(x.asJava).asScala
     }
     JavaPairRDD.fromRDD(
       rdd.mapPartitions(fn, preservesPartitioning))(fakeClassTag[K2], fakeClassTag[V2])
@@ -290,7 +290,7 @@ trait JavaRDDLike[T, This <: JavaRDDLike[T, This]] extends Serializable {
       other: JavaRDDLike[U, _],
       f: FlatMapFunction2[java.util.Iterator[T], java.util.Iterator[U], V]): JavaRDD[V] = {
     def fn: (Iterator[T], Iterator[U]) => Iterator[V] = {
-      (x: Iterator[T], y: Iterator[U]) => f.call(x.asJava, y.asJava).iterator().asScala
+      (x: Iterator[T], y: Iterator[U]) => f.call(x.asJava, y.asJava).asScala
     }
     JavaRDD.fromRDD(
       rdd.zipPartitions(other.rdd)(fn)(other.classTag, fakeClassTag[V]))(fakeClassTag[V])

core/src/test/java/org/apache/spark/JavaAPISuite.java

@@ -880,8 +880,8 @@ public void flatMap() {
       "The quick brown fox jumps over the lazy dog."));
     JavaRDD<String> words = rdd.flatMap(new FlatMapFunction<String, String>() {
       @Override
-      public Iterable<String> call(String x) {
-        return Arrays.asList(x.split(" "));
+      public Iterator<String> call(String x) {
+        return Arrays.asList(x.split(" ")).iterator();
       }
     });
     Assert.assertEquals("Hello", words.first());
@@ -890,12 +890,12 @@ public Iterable<String> call(String x) {
     JavaPairRDD<String, String> pairsRDD = rdd.flatMapToPair(
       new PairFlatMapFunction<String, String, String>() {
         @Override
-        public Iterable<Tuple2<String, String>> call(String s) {
+        public Iterator<Tuple2<String, String>> call(String s) {
           List<Tuple2<String, String>> pairs = new LinkedList<>();
           for (String word : s.split(" ")) {
             pairs.add(new Tuple2<>(word, word));
           }
-          return pairs;
+          return pairs.iterator();
         }
       }
     );
@@ -904,12 +904,12 @@ public Iterable<Tuple2<String, String>> call(String s) {
 
     JavaDoubleRDD doubles = rdd.flatMapToDouble(new DoubleFlatMapFunction<String>() {
       @Override
-      public Iterable<Double> call(String s) {
+      public Iterator<Double> call(String s) {
         List<Double> lengths = new LinkedList<>();
         for (String word : s.split(" ")) {
           lengths.add((double) word.length());
         }
-        return lengths;
+        return lengths.iterator();
       }
     });
     Assert.assertEquals(5.0, doubles.first(), 0.01);
@@ -930,8 +930,8 @@ public void mapsFromPairsToPairs() {
     JavaPairRDD<String, Integer> swapped = pairRDD.flatMapToPair(
       new PairFlatMapFunction<Tuple2<Integer, String>, String, Integer>() {
         @Override
-        public Iterable<Tuple2<String, Integer>> call(Tuple2<Integer, String> item) {
-          return Collections.singletonList(item.swap());
+        public Iterator<Tuple2<String, Integer>> call(Tuple2<Integer, String> item) {
+          return Collections.singletonList(item.swap()).iterator();
         }
       });
     swapped.collect();
@@ -951,12 +951,12 @@ public void mapPartitions() {
     JavaRDD<Integer> partitionSums = rdd.mapPartitions(
       new FlatMapFunction<Iterator<Integer>, Integer>() {
         @Override
-        public Iterable<Integer> call(Iterator<Integer> iter) {
+        public Iterator<Integer> call(Iterator<Integer> iter) {
           int sum = 0;
           while (iter.hasNext()) {
             sum += iter.next();
           }
-          return Collections.singletonList(sum);
+          return Collections.singletonList(sum).iterator();
         }
     });
     Assert.assertEquals("[3, 7]", partitionSums.collect().toString());
@@ -1367,8 +1367,8 @@ public void zipPartitions() {
     FlatMapFunction2<Iterator<Integer>, Iterator<String>, Integer> sizesFn =
       new FlatMapFunction2<Iterator<Integer>, Iterator<String>, Integer>() {
         @Override
-        public Iterable<Integer> call(Iterator<Integer> i, Iterator<String> s) {
-          return Arrays.asList(Iterators.size(i), Iterators.size(s));
+        public Iterator<Integer> call(Iterator<Integer> i, Iterator<String> s) {
+          return Arrays.asList(Iterators.size(i), Iterators.size(s)).iterator();
         }
       };
 

docs/streaming-programming-guide.md

@@ -165,8 +165,8 @@ space into words.
 // Split each line into words
 JavaDStream<String> words = lines.flatMap(
   new FlatMapFunction<String, String>() {
-    @Override public Iterable<String> call(String x) {
-      return Arrays.asList(x.split(" "));
+    @Override public Iterator<String> call(String x) {
+      return Arrays.asList(x.split(" ")).iterator();
     }
   });
 {% endhighlight %}

examples/src/main/java/org/apache/spark/examples/JavaPageRank.java

@@ -17,7 +17,10 @@
 
 package org.apache.spark.examples;
 
-
+import java.util.ArrayList;
+import java.util.List;
+import java.util.Iterator;
+import java.util.regex.Pattern;
 
 import scala.Tuple2;
 
@@ -32,11 +35,6 @@
 import org.apache.spark.api.java.function.PairFlatMapFunction;
 import org.apache.spark.api.java.function.PairFunction;
 
-import java.util.ArrayList;
-import java.util.List;
-import java.util.Iterator;
-import java.util.regex.Pattern;
-
 /**
  * Computes the PageRank of URLs from an input file. Input file should
  * be in format of:
@@ -108,13 +106,13 @@ public Double call(Iterable<String> rs) {
       JavaPairRDD<String, Double> contribs = links.join(ranks).values()
         .flatMapToPair(new PairFlatMapFunction<Tuple2<Iterable<String>, Double>, String, Double>() {
           @Override
-          public Iterable<Tuple2<String, Double>> call(Tuple2<Iterable<String>, Double> s) {
+          public Iterator<Tuple2<String, Double>> call(Tuple2<Iterable<String>, Double> s) {
             int urlCount = Iterables.size(s._1);
-            List<Tuple2<String, Double>> results = new ArrayList<Tuple2<String, Double>>();
+            List<Tuple2<String, Double>> results = new ArrayList<>();
             for (String n : s._1) {
-              results.add(new Tuple2<String, Double>(n, s._2() / urlCount));
+              results.add(new Tuple2<>(n, s._2() / urlCount));
             }
-            return results;
+            return results.iterator();
           }
       });
 

examples/src/main/java/org/apache/spark/examples/JavaWordCount.java

@@ -27,6 +27,7 @@
 import org.apache.spark.api.java.function.PairFunction;
 
 import java.util.Arrays;
+import java.util.Iterator;
 import java.util.List;
 import java.util.regex.Pattern;
 
@@ -46,8 +47,8 @@ public static void main(String[] args) throws Exception {
 
     JavaRDD<String> words = lines.flatMap(new FlatMapFunction<String, String>() {
       @Override
-      public Iterable<String> call(String s) {
-        return Arrays.asList(SPACE.split(s));
+      public Iterator<String> call(String s) {
+        return Arrays.asList(SPACE.split(s)).iterator();
       }
     });
 

examples/src/main/java/org/apache/spark/examples/streaming/JavaActorWordCount.java

@@ -18,6 +18,7 @@
 package org.apache.spark.examples.streaming;
 
 import java.util.Arrays;
+import java.util.Iterator;
 
 import scala.Tuple2;
 
@@ -116,8 +117,8 @@ public static void main(String[] args) {
     // compute wordcount
     lines.flatMap(new FlatMapFunction<String, String>() {
       @Override
-      public Iterable<String> call(String s) {
-        return Arrays.asList(s.split("\\s+"));
+      public Iterator<String> call(String s) {
+        return Arrays.asList(s.split("\\s+")).iterator();
       }
     }).mapToPair(new PairFunction<String, String, Integer>() {
       @Override

examples/src/main/java/org/apache/spark/examples/streaming/JavaCustomReceiver.java

@@ -17,7 +17,6 @@
 
 package org.apache.spark.examples.streaming;
 
-import com.google.common.collect.Lists;
 import com.google.common.io.Closeables;
 
 import org.apache.spark.SparkConf;
@@ -37,6 +36,8 @@
 import java.io.InputStreamReader;
 import java.net.ConnectException;
 import java.net.Socket;
+import java.util.Arrays;
+import java.util.Iterator;
 import java.util.regex.Pattern;
 
 /**
@@ -74,8 +75,8 @@ public static void main(String[] args) {
       new JavaCustomReceiver(args[0], Integer.parseInt(args[1])));
     JavaDStream<String> words = lines.flatMap(new FlatMapFunction<String, String>() {
       @Override
-      public Iterable<String> call(String x) {
-        return Lists.newArrayList(SPACE.split(x));
+      public Iterator<String> call(String x) {
+        return Arrays.asList(SPACE.split(x)).iterator();
       }
     });
     JavaPairDStream<String, Integer> wordCounts = words.mapToPair(

examples/src/main/java/org/apache/spark/examples/streaming/JavaDirectKafkaWordCount.java

@@ -20,11 +20,11 @@
 import java.util.HashMap;
 import java.util.HashSet;
 import java.util.Arrays;
+import java.util.Iterator;
 import java.util.regex.Pattern;
 
 import scala.Tuple2;
 
-import com.google.common.collect.Lists;
 import kafka.serializer.StringDecoder;
 
 import org.apache.spark.SparkConf;
@@ -87,8 +87,8 @@ public String call(Tuple2<String, String> tuple2) {
     });
     JavaDStream<String> words = lines.flatMap(new FlatMapFunction<String, String>() {
       @Override
-      public Iterable<String> call(String x) {
-        return Lists.newArrayList(SPACE.split(x));
+      public Iterator<String> call(String x) {
+        return Arrays.asList(SPACE.split(x)).iterator();
       }
     });
     JavaPairDStream<String, Integer> wordCounts = words.mapToPair(