[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, 2 insertions, 0 deletions

diff --git a/repl/scala-2.10/src/main/scala/org/apache/spark/repl/SparkIMain.scala b/repl/scala-2.10/src/main/scala/org/apache/spark/repl/SparkIMain.scala
index 8791618bd3..4ee605fd7f 100644
--- a/repl/scala-2.10/src/main/scala/org/apache/spark/repl/SparkIMain.scala
+++ b/repl/scala-2.10/src/main/scala/org/apache/spark/repl/SparkIMain.scala
@@ -1079,8 +1079,10 @@ import org.apache.spark.annotation.DeveloperApi
       throw new EvalException("Failed to load '" + path + "': " + ex.getMessage, ex)
 
     private def load(path: String): Class[_] = {
+      // scalastyle:off classforname
       try Class.forName(path, true, classLoader)
       catch { case ex: Throwable => evalError(path, unwrap(ex)) }
+      // scalastyle:on classforname
     }
 
     lazy val evalClass = load(evalPath)