[SPARK-8962] Add Scalastyle rule to ban direct use of Class.forName; fix existing uses

This pull request adds a Scalastyle regex rule which fails the style check if `Class.forName` is used directly.  `Class.forName` always loads classes from the default / system classloader, but in a majority of cases, we should be using Spark's own `Utils.classForName` instead, which tries to load classes from the current thread's context classloader and falls back to the classloader which loaded Spark when the context classloader is not defined.

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Author: Josh Rosen <joshrosen@databricks.com>

Closes #7350 from JoshRosen/ban-Class.forName and squashes the following commits:

e3e96f7 [Josh Rosen] Merge remote-tracking branch 'origin/master' into ban-Class.forName
c0b7885 [Josh Rosen] Hopefully fix the last two cases
d707ba7 [Josh Rosen] Fix uses of Class.forName that I missed in my first cleanup pass
046470d [Josh Rosen] Merge remote-tracking branch 'origin/master' into ban-Class.forName
62882ee [Josh Rosen] Fix uses of Class.forName or add exclusion.
d9abade [Josh Rosen] Add stylechecker rule to ban uses of Class.forName

1 files changed, 3 insertions, 3 deletions

diff --git a/streaming/src/main/scala/org/apache/spark/streaming/scheduler/JobGenerator.scala b/streaming/src/main/scala/org/apache/spark/streaming/scheduler/JobGenerator.scala
index f5d4185864..9f2117ada6 100644
--- a/streaming/src/main/scala/org/apache/spark/streaming/scheduler/JobGenerator.scala
+++ b/streaming/src/main/scala/org/apache/spark/streaming/scheduler/JobGenerator.scala
@@ -22,7 +22,7 @@ import scala.util.{Failure, Success, Try}
 import org.apache.spark.{SparkEnv, Logging}
 import org.apache.spark.streaming.{Checkpoint, CheckpointWriter, Time}
 import org.apache.spark.streaming.util.RecurringTimer
-import org.apache.spark.util.{Clock, EventLoop, ManualClock}
+import org.apache.spark.util.{Utils, Clock, EventLoop, ManualClock}
 
 /** Event classes for JobGenerator */
 private[scheduler] sealed trait JobGeneratorEvent
@@ -47,11 +47,11 @@ class JobGenerator(jobScheduler: JobScheduler) extends Logging {
     val clockClass = ssc.sc.conf.get(
       "spark.streaming.clock", "org.apache.spark.util.SystemClock")
     try {
-      Class.forName(clockClass).newInstance().asInstanceOf[Clock]
+      Utils.classForName(clockClass).newInstance().asInstanceOf[Clock]
     } catch {
       case e: ClassNotFoundException if clockClass.startsWith("org.apache.spark.streaming") =>
         val newClockClass = clockClass.replace("org.apache.spark.streaming", "org.apache.spark")
-        Class.forName(newClockClass).newInstance().asInstanceOf[Clock]
+        Utils.classForName(newClockClass).newInstance().asInstanceOf[Clock]
     }
   }