[SPARK-2525][SQL] Remove as many compilation warning messages as possible in Spark SQL

JIRA: https://issues.apache.org/jira/browse/SPARK-2525.

Author: Yin Huai <huai@cse.ohio-state.edu>

Closes #1444 from yhuai/SPARK-2517 and squashes the following commits:

edbac3f [Yin Huai] Removed some compiler type erasure warnings.

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

@@ -380,32 +380,32 @@ class SchemaRDD(
       val fields = structType.fields.map(field => (field.name, field.dataType))
       val map: JMap[String, Any] = new java.util.HashMap
       row.zip(fields).foreach {
-        case (obj, (name, dataType)) =>
+        case (obj, (attrName, dataType)) =>
           dataType match {
-            case struct: StructType => map.put(name, rowToMap(obj.asInstanceOf[Row], struct))
+            case struct: StructType => map.put(attrName, rowToMap(obj.asInstanceOf[Row], struct))
             case array @ ArrayType(struct: StructType) =>
               val arrayValues = obj match {
                 case seq: Seq[Any] =>
                   seq.map(element => rowToMap(element.asInstanceOf[Row], struct)).asJava
-                case list: JList[Any] =>
+                case list: JList[_] =>
                   list.map(element => rowToMap(element.asInstanceOf[Row], struct))
-                case set: JSet[Any] =>
+                case set: JSet[_] =>
                   set.map(element => rowToMap(element.asInstanceOf[Row], struct))
-                case array if array != null && array.getClass.isArray =>
-                  array.asInstanceOf[Array[Any]].map {
+                case arr if arr != null && arr.getClass.isArray =>
+                  arr.asInstanceOf[Array[Any]].map {
                     element => rowToMap(element.asInstanceOf[Row], struct)
                   }
                 case other => other
               }
-              map.put(name, arrayValues)
+              map.put(attrName, arrayValues)
             case array: ArrayType => {
               val arrayValues = obj match {
                 case seq: Seq[Any] => seq.asJava
                 case other => other
               }
-              map.put(name, arrayValues)
+              map.put(attrName, arrayValues)
             }
-            case other => map.put(name, obj)
+            case other => map.put(attrName, obj)
           }
       }
 

sql/core/src/main/scala/org/apache/spark/sql/json/JsonRDD.scala

@@ -204,14 +204,14 @@ private[sql] object JsonRDD extends Logging {
       case (key, value) => (s"`$key`", value)
     }.toSet
     keyValuePairs.flatMap {
-      case (key: String, struct: Map[String, Any]) => {
-        // The value associted with the key is an JSON object.
-        allKeysWithValueTypes(struct).map {
+      case (key: String, struct: Map[_, _]) => {
+        // The value associated with the key is an JSON object.
+        allKeysWithValueTypes(struct.asInstanceOf[Map[String, Any]]).map {
           case (k, dataType) => (s"$key.$k", dataType)
         } ++ Set((key, StructType(Nil)))
       }
-      case (key: String, array: List[Any]) => {
-        // The value associted with the key is an array.
+      case (key: String, array: List[_]) => {
+        // The value associated with the key is an array.
         typeOfArray(array) match {
           case ArrayType(StructType(Nil)) => {
             // The elements of this arrays are structs.
@@ -235,12 +235,12 @@ private[sql] object JsonRDD extends Logging {
    * the parsing very slow.
    */
   private def scalafy(obj: Any): Any = obj match {
-    case map: java.util.Map[String, Object] =>
+    case map: java.util.Map[_, _] =>
       // .map(identity) is used as a workaround of non-serializable Map
       // generated by .mapValues.
       // This issue is documented at https://issues.scala-lang.org/browse/SI-7005
       map.toMap.mapValues(scalafy).map(identity)
-    case list: java.util.List[Object] =>
+    case list: java.util.List[_] =>
       list.toList.map(scalafy)
     case atom => atom
   }
@@ -320,8 +320,8 @@ private[sql] object JsonRDD extends Logging {
 
   private def toString(value: Any): String = {
     value match {
-      case value: Map[String, Any] => toJsonObjectString(value)
-      case value: Seq[Any] => toJsonArrayString(value)
+      case value: Map[_, _] => toJsonObjectString(value.asInstanceOf[Map[String, Any]])
+      case value: Seq[_] => toJsonArrayString(value)
       case value => Option(value).map(_.toString).orNull
     }
   }

sql/hive/src/test/scala/org/apache/spark/sql/hive/execution/HiveQuerySuite.scala

@@ -390,7 +390,7 @@ class HiveQuerySuite extends HiveComparisonTest {
     hql("CREATE TABLE m(value MAP<INT, STRING>)")
     hql("INSERT OVERWRITE TABLE m SELECT MAP(key, value) FROM src LIMIT 10")
     hql("SELECT * FROM m").collect().zip(hql("SELECT * FROM src LIMIT 10").collect()).map {
-      case (Row(map: Map[Int, String]), Row(key: Int, value: String)) =>
+      case (Row(map: Map[_, _]), Row(key: Int, value: String)) =>
         assert(map.size === 1)
         assert(map.head === (key, value))
     }