[SPARK-11839][ML] refactor save/write traits

* add "ML" prefix to reader/writer/readable/writable to avoid name collision with java.util.*
* define `DefaultParamsReadable/Writable` and use them to save some code
* use `super.load` instead so people can jump directly to the doc of `Readable.load`, which documents the Java compatibility issues

jkbradley

Author: Xiangrui Meng <meng@databricks.com>

Closes #9827 from mengxr/SPARK-11839.

2 files changed, 16 insertions, 15 deletions

diff --git a/mllib/src/test/scala/org/apache/spark/ml/PipelineSuite.scala b/mllib/src/test/scala/org/apache/spark/ml/PipelineSuite.scala
index 7f5c3895ac..12aba6bc6d 100644
--- a/mllib/src/test/scala/org/apache/spark/ml/PipelineSuite.scala
+++ b/mllib/src/test/scala/org/apache/spark/ml/PipelineSuite.scala
@@ -179,8 +179,8 @@ class PipelineSuite extends SparkFunSuite with MLlibTestSparkContext with Defaul
 }
 
 
-/** Used to test [[Pipeline]] with [[Writable]] stages */
-class WritableStage(override val uid: String) extends Transformer with Writable {
+/** Used to test [[Pipeline]] with [[MLWritable]] stages */
+class WritableStage(override val uid: String) extends Transformer with MLWritable {
 
   final val intParam: IntParam = new IntParam(this, "intParam", "doc")
 
@@ -192,21 +192,21 @@ class WritableStage(override val uid: String) extends Transformer with Writable
 
   override def copy(extra: ParamMap): WritableStage = defaultCopy(extra)
 
-  override def write: Writer = new DefaultParamsWriter(this)
+  override def write: MLWriter = new DefaultParamsWriter(this)
 
   override def transform(dataset: DataFrame): DataFrame = dataset
 
   override def transformSchema(schema: StructType): StructType = schema
 }
 
-object WritableStage extends Readable[WritableStage] {
+object WritableStage extends MLReadable[WritableStage] {
 
-  override def read: Reader[WritableStage] = new DefaultParamsReader[WritableStage]
+  override def read: MLReader[WritableStage] = new DefaultParamsReader[WritableStage]
 
-  override def load(path: String): WritableStage = read.load(path)
+  override def load(path: String): WritableStage = super.load(path)
 }
 
-/** Used to test [[Pipeline]] with non-[[Writable]] stages */
+/** Used to test [[Pipeline]] with non-[[MLWritable]] stages */
 class UnWritableStage(override val uid: String) extends Transformer {
 
   final val intParam: IntParam = new IntParam(this, "intParam", "doc")
diff --git a/mllib/src/test/scala/org/apache/spark/ml/util/DefaultReadWriteTest.scala b/mllib/src/test/scala/org/apache/spark/ml/util/DefaultReadWriteTest.scala
index dd1e8acce9..84d06b43d6 100644
--- a/mllib/src/test/scala/org/apache/spark/ml/util/DefaultReadWriteTest.scala
+++ b/mllib/src/test/scala/org/apache/spark/ml/util/DefaultReadWriteTest.scala
@@ -38,7 +38,7 @@ trait DefaultReadWriteTest extends TempDirectory { self: Suite =>
    * @tparam T ML instance type
    * @return  Instance loaded from file
    */
-  def testDefaultReadWrite[T <: Params with Writable](
+  def testDefaultReadWrite[T <: Params with MLWritable](
       instance: T,
       testParams: Boolean = true): T = {
     val uid = instance.uid
@@ -52,7 +52,7 @@ trait DefaultReadWriteTest extends TempDirectory { self: Suite =>
       instance.save(path)
     }
     instance.write.overwrite().save(path)
-    val loader = instance.getClass.getMethod("read").invoke(null).asInstanceOf[Reader[T]]
+    val loader = instance.getClass.getMethod("read").invoke(null).asInstanceOf[MLReader[T]]
     val newInstance = loader.load(path)
 
     assert(newInstance.uid === instance.uid)
@@ -92,7 +92,8 @@ trait DefaultReadWriteTest extends TempDirectory { self: Suite =>
    * @tparam E  Type of [[Estimator]]
    * @tparam M  Type of [[Model]] produced by estimator
    */
-  def testEstimatorAndModelReadWrite[E <: Estimator[M] with Writable, M <: Model[M] with Writable](
+  def testEstimatorAndModelReadWrite[
+    E <: Estimator[M] with MLWritable, M <: Model[M] with MLWritable](
       estimator: E,
       dataset: DataFrame,
       testParams: Map[String, Any],
@@ -119,7 +120,7 @@ trait DefaultReadWriteTest extends TempDirectory { self: Suite =>
   }
 }
 
-class MyParams(override val uid: String) extends Params with Writable {
+class MyParams(override val uid: String) extends Params with MLWritable {
 
   final val intParamWithDefault: IntParam = new IntParam(this, "intParamWithDefault", "doc")
   final val intParam: IntParam = new IntParam(this, "intParam", "doc")
@@ -145,14 +146,14 @@ class MyParams(override val uid: String) extends Params with Writable {
 
   override def copy(extra: ParamMap): Params = defaultCopy(extra)
 
-  override def write: Writer = new DefaultParamsWriter(this)
+  override def write: MLWriter = new DefaultParamsWriter(this)
 }
 
-object MyParams extends Readable[MyParams] {
+object MyParams extends MLReadable[MyParams] {
 
-  override def read: Reader[MyParams] = new DefaultParamsReader[MyParams]
+  override def read: MLReader[MyParams] = new DefaultParamsReader[MyParams]
 
-  override def load(path: String): MyParams = read.load(path)
+  override def load(path: String): MyParams = super.load(path)
 }
 
 class DefaultReadWriteSuite extends SparkFunSuite with MLlibTestSparkContext