Github user squito commented on a diff in the pull request:
https://github.com/apache/spark/pull/19309#discussion_r141712571
--- Diff: core/src/main/scala/org/apache/spark/util/Utils.scala ---
@@ -2687,6 +2688,59 @@ private[spark] object Utils extends Logging {
def stringToSeq(str: String): Seq[String] = {
str.split(",").map(_.trim()).filter(_.nonEmpty)
}
+
+ /**
+ * Create instances of extension classes.
+ *
+ * The classes in the given list must:
+ * - Be sub-classes of the given base class.
+ * - Provide either a no-arg constructor, or a 1-arg constructor that
takes a SparkConf.
+ *
+ * The constructors are allowed to throw "UnsupportedOperationException"
if the extension does not
+ * want to be registered; this allows the implementations to check the
Spark configuration (or
+ * other state) and decide they do not need to be added. A log message
is printed in that case.
+ * Other exceptions are bubbled up.
+ */
+ def loadExtensions[T](extClass: Class[T], classes: Seq[String], conf:
SparkConf): Seq[T] = {
+ classes.flatMap { name =>
+ try {
+ val klass = classForName(name)
+ require(extClass.isAssignableFrom(klass),
+ s"$name is not a subclass of ${extClass.getName()}.")
+
+ val ext = Try(klass.getConstructor(classOf[SparkConf])) match {
+ case Success(ctor) =>
+ ctor.newInstance(conf)
+
+ case Failure(_) =>
+ klass.getConstructor().newInstance()
+ }
+
+ Some(ext.asInstanceOf[T])
+ } catch {
+ case _: NoSuchMethodException =>
+ throw new SparkException(
+ s"$name did not have a zero-argument constructor or a" +
+ " single-argument constructor that accepts SparkConf. Note:
if the class is" +
+ " defined inside of another Scala class, then its
constructors may accept an" +
+ " implicit parameter that references the enclosing class; in
this case, you must" +
+ " define the class as a top-level class in order to prevent
this extra" +
+ " parameter from breaking Spark's ability to find a valid
constructor.")
+
+ case e: InvocationTargetException =>
+ e.getCause() match {
+ case _: UnsupportedOperationException =>
--- End diff --
I am a bit worried catching UnsupportedOperationException is a bit too
general ... what if its thrown by something else deep inside the extension
class? The user won't get to see what happened.
OTOH, I can't think of anything better to catch (doesn't seem worth a
special exception type). Maybe log the entire exception at debug level?
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