[SPARK-9486][SQL] Add data source aliasing for external packages

Users currently have to provide the full class name for external data sources, like:

`sqlContext.read.format("com.databricks.spark.avro").load(path)`

This allows external data source packages to register themselves using a Service Loader so that they can add custom alias like:

`sqlContext.read.format("avro").load(path)`

This makes it so that using external data source packages uses the same format as the internal data sources like parquet, json, etc.

Author: Joseph Batchik <joseph.batchik@cloudera.com>
Author: Joseph Batchik <josephbatchik@gmail.com>

Closes #7802 from JDrit/service_loader and squashes the following commits:

49a01ec [Joseph Batchik] fixed a couple of format / error bugs
e5e93b2 [Joseph Batchik] modified rat file to only excluded added services
72b349a [Joseph Batchik] fixed error with orc data source actually
9f93ea7 [Joseph Batchik] fixed error with orc data source
87b7f1c [Joseph Batchik] fixed typo
101cd22 [Joseph Batchik] removing unneeded changes
8f3cf43 [Joseph Batchik] merged in changes
b63d337 [Joseph Batchik] merged in master
95ae030 [Joseph Batchik] changed the new trait to be used as a mixin for data source to register themselves
74db85e [Joseph Batchik] reformatted class loader
ac2270d [Joseph Batchik] removing some added test
a6926db [Joseph Batchik] added test cases for data source loader
208a2a8 [Joseph Batchik] changes to do error catching if there are multiple data sources
946186e [Joseph Batchik] started working on service loader

6 files changed, 62 insertions, 29 deletions

diff --git a/sql/core/src/main/resources/META-INF/services/org.apache.spark.sql.sources.DataSourceRegister b/sql/core/src/main/resources/META-INF/services/org.apache.spark.sql.sources.DataSourceRegister
new file mode 100644
index 0000000000..cc32d4b727
--- /dev/null
+++ b/sql/core/src/main/resources/META-INF/services/org.apache.spark.sql.sources.DataSourceRegister
@@ -0,0 +1,3 @@
+org.apache.spark.sql.jdbc.DefaultSource
+org.apache.spark.sql.json.DefaultSource
+org.apache.spark.sql.parquet.DefaultSource
diff --git a/sql/core/src/main/scala/org/apache/spark/sql/execution/datasources/ddl.scala b/sql/core/src/main/scala/org/apache/spark/sql/execution/datasources/ddl.scala
index 0cdb407ad5..8c2f297e42 100644
--- a/sql/core/src/main/scala/org/apache/spark/sql/execution/datasources/ddl.scala
+++ b/sql/core/src/main/scala/org/apache/spark/sql/execution/datasources/ddl.scala
@@ -17,7 +17,12 @@
 
 package org.apache.spark.sql.execution.datasources
 
+import java.util.ServiceLoader
+
+import scala.collection.Iterator
+import scala.collection.JavaConversions._
 import scala.language.{existentials, implicitConversions}
+import scala.util.{Failure, Success, Try}
 import scala.util.matching.Regex
 
 import org.apache.hadoop.fs.Path
@@ -190,37 +195,32 @@ private[sql] class DDLParser(
     }
 }
 
-private[sql] object ResolvedDataSource {
-
-  private val builtinSources = Map(
-    "jdbc" -> "org.apache.spark.sql.jdbc.DefaultSource",
-    "json" -> "org.apache.spark.sql.json.DefaultSource",
-    "parquet" -> "org.apache.spark.sql.parquet.DefaultSource",
-    "orc" -> "org.apache.spark.sql.hive.orc.DefaultSource"
-  )
+private[sql] object ResolvedDataSource extends Logging {
 
   /** Given a provider name, look up the data source class definition. */
   def lookupDataSource(provider: String): Class[_] = {
+    val provider2 = s"$provider.DefaultSource"
     val loader = Utils.getContextOrSparkClassLoader
-
-    if (builtinSources.contains(provider)) {
-      return loader.loadClass(builtinSources(provider))
-    }
-
-    try {
-      loader.loadClass(provider)
-    } catch {
-      case cnf: java.lang.ClassNotFoundException =>
-        try {
-          loader.loadClass(provider + ".DefaultSource")
-        } catch {
-          case cnf: java.lang.ClassNotFoundException =>
-            if (provider.startsWith("org.apache.spark.sql.hive.orc")) {
-              sys.error("The ORC data source must be used with Hive support enabled.")
-            } else {
-              sys.error(s"Failed to load class for data source: $provider")
-            }
+    val serviceLoader = ServiceLoader.load(classOf[DataSourceRegister], loader)
+
+    serviceLoader.iterator().filter(_.format().equalsIgnoreCase(provider)).toList match {
+      /** the provider format did not match any given registered aliases */
+      case Nil => Try(loader.loadClass(provider)).orElse(Try(loader.loadClass(provider2))) match {
+        case Success(dataSource) => dataSource
+        case Failure(error) => if (provider.startsWith("org.apache.spark.sql.hive.orc")) {
+          throw new ClassNotFoundException(
+            "The ORC data source must be used with Hive support enabled.", error)
+        } else {
+          throw new ClassNotFoundException(
+            s"Failed to load class for data source: $provider", error)
         }
+      }
+      /** there is exactly one registered alias */
+      case head :: Nil => head.getClass
+      /** There are multiple registered aliases for the input */
+      case sources => sys.error(s"Multiple sources found for $provider, " +
+        s"(${sources.map(_.getClass.getName).mkString(", ")}), " +
+        "please specify the fully qualified class name")
     }
   }
 
diff --git a/sql/core/src/main/scala/org/apache/spark/sql/jdbc/JDBCRelation.scala b/sql/core/src/main/scala/org/apache/spark/sql/jdbc/JDBCRelation.scala
index 41d0ecb4bb..48d97ced9c 100644
--- a/sql/core/src/main/scala/org/apache/spark/sql/jdbc/JDBCRelation.scala
+++ b/sql/core/src/main/scala/org/apache/spark/sql/jdbc/JDBCRelation.scala
@@ -77,7 +77,10 @@ private[sql] object JDBCRelation {
   }
 }
 
-private[sql] class DefaultSource extends RelationProvider {
+private[sql] class DefaultSource extends RelationProvider with DataSourceRegister {
+
+  def format(): String = "jdbc"
+
   /** Returns a new base relation with the given parameters. */
   override def createRelation(
       sqlContext: SQLContext,
diff --git a/sql/core/src/main/scala/org/apache/spark/sql/json/JSONRelation.scala b/sql/core/src/main/scala/org/apache/spark/sql/json/JSONRelation.scala
index 10f1367e69..b34a272ec5 100644
--- a/sql/core/src/main/scala/org/apache/spark/sql/json/JSONRelation.scala
+++ b/sql/core/src/main/scala/org/apache/spark/sql/json/JSONRelation.scala
@@ -37,7 +37,10 @@ import org.apache.spark.sql.sources._
 import org.apache.spark.sql.types.StructType
 import org.apache.spark.sql.{AnalysisException, Row, SQLContext}
 
-private[sql] class DefaultSource extends HadoopFsRelationProvider {
+private[sql] class DefaultSource extends HadoopFsRelationProvider with DataSourceRegister {
+
+  def format(): String = "json"
+
   override def createRelation(
       sqlContext: SQLContext,
       paths: Array[String],
diff --git a/sql/core/src/main/scala/org/apache/spark/sql/parquet/ParquetRelation.scala b/sql/core/src/main/scala/org/apache/spark/sql/parquet/ParquetRelation.scala
index 48009b2fd0..b6db71b5b8 100644
--- a/sql/core/src/main/scala/org/apache/spark/sql/parquet/ParquetRelation.scala
+++ b/sql/core/src/main/scala/org/apache/spark/sql/parquet/ParquetRelation.scala
@@ -49,7 +49,10 @@ import org.apache.spark.sql.types.{DataType, StructType}
 import org.apache.spark.util.{SerializableConfiguration, Utils}
 
 
-private[sql] class DefaultSource extends HadoopFsRelationProvider {
+private[sql] class DefaultSource extends HadoopFsRelationProvider with DataSourceRegister {
+
+  def format(): String = "parquet"
+
   override def createRelation(
       sqlContext: SQLContext,
       paths: Array[String],
diff --git a/sql/core/src/main/scala/org/apache/spark/sql/sources/interfaces.scala b/sql/core/src/main/scala/org/apache/spark/sql/sources/interfaces.scala
index c5b7ee73eb..4aafec0e2d 100644
--- a/sql/core/src/main/scala/org/apache/spark/sql/sources/interfaces.scala
+++ b/sql/core/src/main/scala/org/apache/spark/sql/sources/interfaces.scala
@@ -39,6 +39,27 @@ import org.apache.spark.util.SerializableConfiguration
 
 /**
  * ::DeveloperApi::
+ * Data sources should implement this trait so that they can register an alias to their data source.
+ * This allows users to give the data source alias as the format type over the fully qualified
+ * class name.
+ *
+ * ex: parquet.DefaultSource.format = "parquet".
+ *
+ * A new instance of this class with be instantiated each time a DDL call is made.
+ */
+@DeveloperApi
+trait DataSourceRegister {
+
+  /**
+   * The string that represents the format that this data source provider uses. This is
+   * overridden by children to provide a nice alias for the data source,
+   * ex: override def format(): String = "parquet"
+   */
+  def format(): String
+}
+
+/**
+ * ::DeveloperApi::
  * Implemented by objects that produce relations for a specific kind of data source.  When
  * Spark SQL is given a DDL operation with a USING clause specified (to specify the implemented
  * RelationProvider), this interface is used to pass in the parameters specified by a user.