Refector code and expand comment.

core/src/main/scala/org/apache/spark/executor/Executor.scala

@@ -222,17 +222,16 @@ private[spark] class Executor(
 
   private val appStartTime = conf.getLong("spark.app.startTime", 0)
 
-  // Jars and files specified by spark.jars and spark.files.
-  private val initialUserJars =
-    conf.getOption("spark.app.initial.jar.urls").map { urls =>
+  // To allow users to distribute plugins and their required files
+  // specified by --jars and --files on application submission, those jars/files should be
+  // downloaded and added to the class loader via updateDependencies.
+  // This should be done before plugin initialization below
+  // because executors search plugins from the class loader and initialize them.
+  private val Seq(initialUserJars, initialUserFiles) = Seq("jar", "file").map { key =>
+    conf.getOption(s"spark.app.initial.$key.urls").map { urls =>
       Map(urls.split(",").map(url => (url, appStartTime)): _*)
     }.getOrElse(Map.empty)
-
-  private val initialUserFiles =
-    conf.getOption("spark.app.initial.file.urls").map { urls =>
-      Map(urls.split(",").map(url => (url, appStartTime)): _*)
-    }.getOrElse(Map.empty)
-
+  }
   updateDependencies(initialUserFiles, initialUserJars)
 
   // Plugins need to load using a class loader that includes the executor's user classpath.

core/src/test/scala/org/apache/spark/deploy/SparkSubmitSuite.scala

@@ -1221,7 +1221,6 @@ class SparkSubmitSuite
     testRemoteResources(enableHttpFs = true, forceDownloadSchemes = Seq("*"))
   }
 
-
   test("SPARK-32119: Jars and files should be loaded when Executors launch for plugins") {
     val tempDir = Utils.createTempDir()
     val tempFileName = "test.txt"