Github user liancheng commented on a diff in the pull request:
https://github.com/apache/spark/pull/2701#discussion_r18872439
--- Diff:
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/util/Metadata.scala
---
@@ -0,0 +1,252 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements. See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License. You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.spark.sql.catalyst.util
+
+import scala.collection.mutable
+
+import org.json4s._
+import org.json4s.jackson.JsonMethods._
+
+/**
+ * Metadata is a wrapper over Map[String, Any] that limits the value type
to simple ones: Boolean,
+ * Long, Double, String, Metadata, Array[Boolean], Array[Long],
Array[Double], Array[String], and
+ * Array[Metadata]. JSON is used for serialization.
+ *
+ * The default constructor is private. User should use either
[[MetadataBuilder]] or
+ * [[Metadata$#fromJson]] to create Metadata instances.
+ *
+ * @param map an immutable map that stores the data
+ */
+sealed class Metadata private[util] (private[util] val map: Map[String,
Any]) extends Serializable {
+
+ /** Gets a Long. */
+ def getLong(key: String): Long = get(key)
+
+ /** Gets a Double. */
+ def getDouble(key: String): Double = get(key)
+
+ /** Gets a Boolean. */
+ def getBoolean(key: String): Boolean = get(key)
+
+ /** Gets a String. */
+ def getString(key: String): String = get(key)
+
+ /** Gets a Metadata. */
+ def getMetadata(key: String): Metadata = get(key)
+
+ /** Gets a Long array. */
+ def getLongArray(key: String): Array[Long] = get(key)
+
+ /** Gets a Double array. */
+ def getDoubleArray(key: String): Array[Double] = get(key)
+
+ /** Gets a Boolean array. */
+ def getBooleanArray(key: String): Array[Boolean] = get(key)
+
+ /** Gets a String array. */
+ def getStringArray(key: String): Array[String] = get(key)
+
+ /** Gets a Metadata array. */
+ def getMetadataArray(key: String): Array[Metadata] = get(key)
+
+ /** Converts to its JSON representation. */
+ def json: String = compact(render(jsonValue))
+
+ override def toString: String = json
+
+ override def equals(obj: Any): Boolean = {
+ obj match {
+ case that: Metadata =>
+ if (map.keySet == that.map.keySet) {
+ map.keys.forall { k =>
+ (map(k), that.map(k)) match {
+ case (v0: Array[_], v1: Array[_]) =>
+ v0.view == v1.view
+ case (v0, v1) =>
+ v0 == v1
+ }
+ }
+ } else {
+ false
+ }
+ case other =>
+ false
+ }
+ }
+
+ override def hashCode: Int = Metadata.hash(this)
+
+ private def get[T](key: String): T = {
+ map(key).asInstanceOf[T]
+ }
+
+ private[sql] def jsonValue: JValue = Metadata.toJsonValue(this)
+}
+
+object Metadata {
+
+ /** Returns an empty Metadata. */
+ def empty: Metadata = new Metadata(Map.empty)
+
+ /** Creates a Metadata instance from JSON. */
+ def fromJson(json: String): Metadata = {
+ fromJObject(parse(json).asInstanceOf[JObject])
+ }
+
+ /** Creates a Metadata instance from JSON AST. */
+ private[sql] def fromJObject(jObj: JObject): Metadata = {
+ val builder = new MetadataBuilder
+ jObj.obj.foreach {
+ case (key, JInt(value)) =>
+ builder.putLong(key, value.toLong)
+ case (key, JDouble(value)) =>
+ builder.putDouble(key, value)
+ case (key, JBool(value)) =>
+ builder.putBoolean(key, value)
+ case (key, JString(value)) =>
+ builder.putString(key, value)
+ case (key, o: JObject) =>
+ builder.putMetadata(key, fromJObject(o))
+ case (key, JArray(value)) =>
+ if (value.isEmpty) {
+ // If it is an empty array, we cannot infer its element type. We
put an empty Array[Long].
+ builder.putLongArray(key, Array.empty)
+ } else {
+ value.head match {
+ case _: JInt =>
+ builder.putLongArray(key,
value.asInstanceOf[List[JInt]].map(_.num.toLong).toArray)
+ case _: JDouble =>
+ builder.putDoubleArray(key,
value.asInstanceOf[List[JDouble]].map(_.num).toArray)
+ case _: JBool =>
+ builder.putBooleanArray(key,
value.asInstanceOf[List[JBool]].map(_.value).toArray)
+ case _: JString =>
+ builder.putStringArray(key,
value.asInstanceOf[List[JString]].map(_.s).toArray)
+ case _: JObject =>
+ builder.putMetadataArray(
+ key,
value.asInstanceOf[List[JObject]].map(fromJObject).toArray)
+ case other =>
+ throw new RuntimeException(s"Do not support array of type
${other.getClass}.")
+ }
+ }
+ case other =>
+ throw new RuntimeException(s"Do not support type
${other.getClass}.")
+ }
+ builder.build()
+ }
+
+ /** Converts to JSON AST. */
+ private def toJsonValue(obj: Any): JValue = {
+ obj match {
+ case map: Map[_, _] =>
+ val fields = map.toList.map { case (k: String, v) => (k,
toJsonValue(v))}
--- End diff --
This `case` branch can be simplified to:
```scala
case map: Map[String, _] =>
JObject(map.mapValues(toJsonValue).toList)
```
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