[SPARK-11810][SQL] Java-based encoder for opaque types in Datasets.

This patch refactors the existing Kryo encoder expressions and adds support for Java serialization.

Author: Reynold Xin <rxin@databricks.com>

Closes #9802 from rxin/SPARK-11810.

3 files changed, 96 insertions, 39 deletions

diff --git a/sql/catalyst/src/main/scala/org/apache/spark/sql/Encoder.scala b/sql/catalyst/src/main/scala/org/apache/spark/sql/Encoder.scala
index 79c2255641..1ed5111440 100644
--- a/sql/catalyst/src/main/scala/org/apache/spark/sql/Encoder.scala
+++ b/sql/catalyst/src/main/scala/org/apache/spark/sql/Encoder.scala
@@ -20,7 +20,7 @@ package org.apache.spark.sql
 import scala.reflect.{ClassTag, classTag}
 
 import org.apache.spark.sql.catalyst.encoders.{ExpressionEncoder, encoderFor}
-import org.apache.spark.sql.catalyst.expressions.{DeserializeWithKryo, BoundReference, SerializeWithKryo}
+import org.apache.spark.sql.catalyst.expressions.{DecodeUsingSerializer, BoundReference, EncodeUsingSerializer}
 import org.apache.spark.sql.types._
 
 /**
@@ -43,28 +43,49 @@ trait Encoder[T] extends Serializable {
  */
 object Encoders {
 
-  /**
-   * (Scala-specific) Creates an encoder that serializes objects of type T using Kryo.
-   * This encoder maps T into a single byte array (binary) field.
-   */
-  def kryo[T: ClassTag]: Encoder[T] = {
-    val ser = SerializeWithKryo(BoundReference(0, ObjectType(classOf[AnyRef]), nullable = true))
-    val deser = DeserializeWithKryo[T](BoundReference(0, BinaryType, nullable = true), classTag[T])
+  /** A way to construct encoders using generic serializers. */
+  private def genericSerializer[T: ClassTag](useKryo: Boolean): Encoder[T] = {
     ExpressionEncoder[T](
       schema = new StructType().add("value", BinaryType),
       flat = true,
-      toRowExpressions = Seq(ser),
-      fromRowExpression = deser,
+      toRowExpressions = Seq(
+        EncodeUsingSerializer(
+          BoundReference(0, ObjectType(classOf[AnyRef]), nullable = true), kryo = useKryo)),
+      fromRowExpression =
+        DecodeUsingSerializer[T](
+          BoundReference(0, BinaryType, nullable = true), classTag[T], kryo = useKryo),
       clsTag = classTag[T]
     )
   }
 
   /**
+   * (Scala-specific) Creates an encoder that serializes objects of type T using Kryo.
+   * This encoder maps T into a single byte array (binary) field.
+   */
+  def kryo[T: ClassTag]: Encoder[T] = genericSerializer(useKryo = true)
+
+  /**
    * Creates an encoder that serializes objects of type T using Kryo.
    * This encoder maps T into a single byte array (binary) field.
    */
   def kryo[T](clazz: Class[T]): Encoder[T] = kryo(ClassTag[T](clazz))
 
+  /**
+   * (Scala-specific) Creates an encoder that serializes objects of type T using generic Java
+   * serialization. This encoder maps T into a single byte array (binary) field.
+   *
+   * Note that this is extremely inefficient and should only be used as the last resort.
+   */
+  def javaSerialization[T: ClassTag]: Encoder[T] = genericSerializer(useKryo = false)
+
+  /**
+   * Creates an encoder that serializes objects of type T using generic Java serialization.
+   * This encoder maps T into a single byte array (binary) field.
+   *
+   * Note that this is extremely inefficient and should only be used as the last resort.
+   */
+  def javaSerialization[T](clazz: Class[T]): Encoder[T] = javaSerialization(ClassTag[T](clazz))
+
   def BOOLEAN: Encoder[java.lang.Boolean] = ExpressionEncoder(flat = true)
   def BYTE: Encoder[java.lang.Byte] = ExpressionEncoder(flat = true)
   def SHORT: Encoder[java.lang.Short] = ExpressionEncoder(flat = true)
diff --git a/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/objects.scala b/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/objects.scala
index 489c6126f8..acf0da2400 100644
--- a/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/objects.scala
+++ b/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/objects.scala
@@ -21,7 +21,7 @@ import scala.language.existentials
 import scala.reflect.ClassTag
 
 import org.apache.spark.SparkConf
-import org.apache.spark.serializer.{KryoSerializerInstance, KryoSerializer}
+import org.apache.spark.serializer._
 import org.apache.spark.sql.Row
 import org.apache.spark.sql.catalyst.analysis.SimpleAnalyzer
 import org.apache.spark.sql.catalyst.plans.logical.{Project, LocalRelation}
@@ -517,29 +517,39 @@ case class GetInternalRowField(child: Expression, ordinal: Int, dataType: DataTy
   }
 }
 
-/** Serializes an input object using Kryo serializer. */
-case class SerializeWithKryo(child: Expression) extends UnaryExpression {
+/**
+ * Serializes an input object using a generic serializer (Kryo or Java).
+ * @param kryo if true, use Kryo. Otherwise, use Java.
+ */
+case class EncodeUsingSerializer(child: Expression, kryo: Boolean) extends UnaryExpression {
 
   override def eval(input: InternalRow): Any =
     throw new UnsupportedOperationException("Only code-generated evaluation is supported")
 
   override protected def genCode(ctx: CodeGenContext, ev: GeneratedExpressionCode): String = {
-    val input = child.gen(ctx)
-    val kryo = ctx.freshName("kryoSerializer")
-    val kryoClass = classOf[KryoSerializer].getName
-    val kryoInstanceClass = classOf[KryoSerializerInstance].getName
-    val sparkConfClass = classOf[SparkConf].getName
+    // Code to initialize the serializer.
+    val serializer = ctx.freshName("serializer")
+    val (serializerClass, serializerInstanceClass) = {
+      if (kryo) {
+        (classOf[KryoSerializer].getName, classOf[KryoSerializerInstance].getName)
+      } else {
+        (classOf[JavaSerializer].getName, classOf[JavaSerializerInstance].getName)
+      }
+    }
+    val sparkConf = s"new ${classOf[SparkConf].getName}()"
     ctx.addMutableState(
-      kryoInstanceClass,
-      kryo,
-      s"$kryo = ($kryoInstanceClass) new $kryoClass(new $sparkConfClass()).newInstance();")
+      serializerInstanceClass,
+      serializer,
+      s"$serializer = ($serializerInstanceClass) new $serializerClass($sparkConf).newInstance();")
 
+    // Code to serialize.
+    val input = child.gen(ctx)
     s"""
       ${input.code}
       final boolean ${ev.isNull} = ${input.isNull};
       ${ctx.javaType(dataType)} ${ev.value} = ${ctx.defaultValue(dataType)};
       if (!${ev.isNull}) {
-        ${ev.value} = $kryo.serialize(${input.value}, null).array();
+        ${ev.value} = $serializer.serialize(${input.value}, null).array();
       }
      """
   }
@@ -548,29 +558,38 @@ case class SerializeWithKryo(child: Expression) extends UnaryExpression {
 }
 
 /**
- * Deserializes an input object using Kryo serializer. Note that the ClassTag is not an implicit
- * parameter because TreeNode cannot copy implicit parameters.
+ * Serializes an input object using a generic serializer (Kryo or Java).  Note that the ClassTag
+ * is not an implicit parameter because TreeNode cannot copy implicit parameters.
+ * @param kryo if true, use Kryo. Otherwise, use Java.
  */
-case class DeserializeWithKryo[T](child: Expression, tag: ClassTag[T]) extends UnaryExpression {
+case class DecodeUsingSerializer[T](child: Expression, tag: ClassTag[T], kryo: Boolean)
+  extends UnaryExpression {
 
   override protected def genCode(ctx: CodeGenContext, ev: GeneratedExpressionCode): String = {
-    val input = child.gen(ctx)
-    val kryo = ctx.freshName("kryoSerializer")
-    val kryoClass = classOf[KryoSerializer].getName
-    val kryoInstanceClass = classOf[KryoSerializerInstance].getName
-    val sparkConfClass = classOf[SparkConf].getName
+    // Code to initialize the serializer.
+    val serializer = ctx.freshName("serializer")
+    val (serializerClass, serializerInstanceClass) = {
+      if (kryo) {
+        (classOf[KryoSerializer].getName, classOf[KryoSerializerInstance].getName)
+      } else {
+        (classOf[JavaSerializer].getName, classOf[JavaSerializerInstance].getName)
+      }
+    }
+    val sparkConf = s"new ${classOf[SparkConf].getName}()"
     ctx.addMutableState(
-      kryoInstanceClass,
-      kryo,
-      s"$kryo = ($kryoInstanceClass) new $kryoClass(new $sparkConfClass()).newInstance();")
+      serializerInstanceClass,
+      serializer,
+      s"$serializer = ($serializerInstanceClass) new $serializerClass($sparkConf).newInstance();")
 
+    // Code to serialize.
+    val input = child.gen(ctx)
     s"""
       ${input.code}
       final boolean ${ev.isNull} = ${input.isNull};
       ${ctx.javaType(dataType)} ${ev.value} = ${ctx.defaultValue(dataType)};
       if (!${ev.isNull}) {
         ${ev.value} = (${ctx.javaType(dataType)})
-          $kryo.deserialize(java.nio.ByteBuffer.wrap(${input.value}), null);
+          $serializer.deserialize(java.nio.ByteBuffer.wrap(${input.value}), null);
       }
      """
   }
diff --git a/sql/catalyst/src/test/scala/org/apache/spark/sql/catalyst/encoders/FlatEncoderSuite.scala b/sql/catalyst/src/test/scala/org/apache/spark/sql/catalyst/encoders/FlatEncoderSuite.scala
index 2729db8489..6e0322fb6e 100644
--- a/sql/catalyst/src/test/scala/org/apache/spark/sql/catalyst/encoders/FlatEncoderSuite.scala
+++ b/sql/catalyst/src/test/scala/org/apache/spark/sql/catalyst/encoders/FlatEncoderSuite.scala
@@ -76,17 +76,34 @@ class FlatEncoderSuite extends ExpressionEncoderSuite {
   // Kryo encoders
   encodeDecodeTest(
     "hello",
-    Encoders.kryo[String].asInstanceOf[ExpressionEncoder[String]],
+    encoderFor(Encoders.kryo[String]),
     "kryo string")
   encodeDecodeTest(
-    new NotJavaSerializable(15),
-    Encoders.kryo[NotJavaSerializable].asInstanceOf[ExpressionEncoder[NotJavaSerializable]],
+    new KryoSerializable(15),
+    encoderFor(Encoders.kryo[KryoSerializable]),
     "kryo object serialization")
+
+  // Java encoders
+  encodeDecodeTest(
+    "hello",
+    encoderFor(Encoders.javaSerialization[String]),
+    "java string")
+  encodeDecodeTest(
+    new JavaSerializable(15),
+    encoderFor(Encoders.javaSerialization[JavaSerializable]),
+    "java object serialization")
 }
 
+/** For testing Kryo serialization based encoder. */
+class KryoSerializable(val value: Int) {
+  override def equals(other: Any): Boolean = {
+    this.value == other.asInstanceOf[KryoSerializable].value
+  }
+}
 
-class NotJavaSerializable(val value: Int) {
+/** For testing Java serialization based encoder. */
+class JavaSerializable(val value: Int) extends Serializable {
   override def equals(other: Any): Boolean = {
-    this.value == other.asInstanceOf[NotJavaSerializable].value
+    this.value == other.asInstanceOf[JavaSerializable].value
   }
 }