[SPARK-26137][CORE] Use Java system property "file.separator" inste…

core/src/main/scala/org/apache/spark/deploy/DependencyUtils.scala

@@ -61,11 +61,12 @@ private[deploy] object DependencyUtils extends Logging {
       hadoopConf: Configuration,
       secMgr: SecurityManager): String = {
     val targetDir = Utils.createTempDir()
+    val userJarName = userJar.split(File.separatorChar).last
     Option(jars)
       .map {
         resolveGlobPaths(_, hadoopConf)
           .split(",")
-          .filterNot(_.contains(userJar.split("/").last))
+          .filterNot(_.contains(userJarName))
           .mkString(",")
       }
       .filterNot(_ == "")

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

@@ -962,6 +962,25 @@ class SparkSubmitSuite
     }
   }
 
+  test("remove copies of application jar from classpath") {
+    val fs = File.separator
+    val sparkConf = new SparkConf(false)
+    val hadoopConf = new Configuration()
+    val secMgr = new SecurityManager(sparkConf)
+
+    val appJarName = "myApp.jar"
+    val jar1Name = "myJar1.jar"
+    val jar2Name = "myJar2.jar"
+    val userJar = s"file:/path${fs}to${fs}app${fs}jar$fs$appJarName"
+    val jars = s"file:/$jar1Name,file:/$appJarName,file:/$jar2Name"
+
+    val resolvedJars = DependencyUtils
+      .resolveAndDownloadJars(jars, userJar, sparkConf, hadoopConf, secMgr)
+
+    assert(!resolvedJars.contains(appJarName))
+    assert(resolvedJars.contains(jar1Name) && resolvedJars.contains(jar2Name))
+  }
+
   test("Avoid re-upload remote resources in yarn client mode") {
     val hadoopConf = new Configuration()
     updateConfWithFakeS3Fs(hadoopConf)