[SPARK-19707][Core] Improve the invalid path check for sc.addJar

core/src/main/scala/org/apache/spark/SparkContext.scala

@@ -1815,10 +1815,18 @@ class SparkContext(config: SparkConf) extends Logging {
           // A JAR file which exists only on the driver node
           case null | "file" =>
             try {
+              val file = new File(uri.getPath)
+              if (!file.exists()) {
+                throw new FileNotFoundException(s"Jar ${file.getAbsolutePath} not found")
+              }
+              if (file.isDirectory) {
+                throw new IllegalArgumentException(
+                  s"Directory ${file.getAbsoluteFile} is not allowed for addJar")
+              }
               env.rpcEnv.fileServer.addJar(new File(uri.getPath))
             } catch {
-              case exc: FileNotFoundException =>
-                logError(s"Jar not found at $path")
+              case NonFatal(e) =>
+                logError(s"Failed to add $path to Spark environment", e)
                 null
             }
           // A JAR file which exists locally on every worker node

core/src/main/scala/org/apache/spark/util/Utils.scala

@@ -1989,7 +1989,7 @@ private[spark] object Utils extends Logging {
     if (paths == null || paths.trim.isEmpty) {
       ""
     } else {
-      paths.split(",").map { p => Utils.resolveURI(p) }.mkString(",")
+      paths.split(",").filter(_.trim.nonEmpty).map { p => Utils.resolveURI(p) }.mkString(",")
     }
   }
 

core/src/test/scala/org/apache/spark/SparkContextSuite.scala

@@ -292,6 +292,22 @@ class SparkContextSuite extends SparkFunSuite with LocalSparkContext with Eventu
     }
   }
 
+  test("add jar with invalid path") {
+    val tmpDir = Utils.createTempDir()
+    val tmpJar = File.createTempFile("test", ".jar", tmpDir)
+
+    sc = new SparkContext(new SparkConf().setAppName("test").setMaster("local"))
+    sc.addJar(tmpJar.getAbsolutePath)
+
+    // Invaid jar path will only print the error log, will not add to file server.
+    sc.addJar("dummy.jar")
+    sc.addJar("")
+    sc.addJar(tmpDir.getAbsolutePath)
+
+    sc.listJars().size should be (1)
+    sc.listJars().head should include (tmpJar.getName)
+  }
+
   test("Cancelling job group should not cause SparkContext to shutdown (SPARK-6414)") {
     try {
       sc = new SparkContext(new SparkConf().setAppName("test").setMaster("local"))

core/src/test/scala/org/apache/spark/util/UtilsSuite.scala

@@ -507,6 +507,7 @@ class UtilsSuite extends SparkFunSuite with ResetSystemProperties with Logging {
       assertResolves("""hdfs:/jar1,file:/jar2,jar3,C:\pi.py#py.pi,C:\path to\jar4""",
         s"hdfs:/jar1,file:/jar2,file:$cwd/jar3,file:/C:/pi.py%23py.pi,file:/C:/path%20to/jar4")
     }
+    assertResolves(",jar1,jar2", s"file:$cwd/jar1,file:$cwd/jar2")
   }
 
   test("nonLocalPaths") {