[SPARK-22403][SS] Add optional checkpointLocation argument to Structu…

…redKafkaWordCount example

## What changes were proposed in this pull request?

When run in YARN cluster mode, the StructuredKafkaWordCount example fails because Spark tries to create a temporary checkpoint location in a subdirectory of the path given by java.io.tmpdir, and YARN sets java.io.tmpdir to a path in the local filesystem that usually does not correspond to an existing path in the distributed filesystem.
Add an optional checkpointLocation argument to the StructuredKafkaWordCount example so that users can specify the checkpoint location and avoid this issue.

## How was this patch tested?

Built and ran the example manually on YARN client and cluster mode.

Author: Wing Yew Poon <wypoon@cloudera.com>

Closes #19703 from wypoon/SPARK-22403.

examples/src/main/scala/org/apache/spark/examples/sql/streaming/StructuredKafkaWordCount.scala

@@ -18,11 +18,14 @@
 // scalastyle:off println
 package org.apache.spark.examples.sql.streaming
 
+import java.util.UUID
+
 import org.apache.spark.sql.SparkSession
 
 /**
  * Consumes messages from one or more topics in Kafka and does wordcount.
  * Usage: StructuredKafkaWordCount <bootstrap-servers> <subscribe-type> <topics>
+ *     [<checkpoint-location>]
  *   <bootstrap-servers> The Kafka "bootstrap.servers" configuration. A
  *   comma-separated list of host:port.
  *   <subscribe-type> There are three kinds of type, i.e. 'assign', 'subscribe',
@@ -36,6 +39,8 @@ import org.apache.spark.sql.SparkSession
  *   |- Only one of "assign, "subscribe" or "subscribePattern" options can be
  *   |  specified for Kafka source.
  *   <topics> Different value format depends on the value of 'subscribe-type'.
+ *   <checkpoint-location> Directory in which to create checkpoints. If not
+ *   provided, defaults to a randomized directory in /tmp.
  *
  * Example:
  *    `$ bin/run-example \
@@ -46,11 +51,13 @@ object StructuredKafkaWordCount {
   def main(args: Array[String]): Unit = {
     if (args.length < 3) {
       System.err.println("Usage: StructuredKafkaWordCount <bootstrap-servers> " +
-        "<subscribe-type> <topics>")
+        "<subscribe-type> <topics> [<checkpoint-location>]")
       System.exit(1)
     }
 
-    val Array(bootstrapServers, subscribeType, topics) = args
+    val Array(bootstrapServers, subscribeType, topics, _*) = args
+    val checkpointLocation =
+      if (args.length > 3) args(3) else "/tmp/temporary-" + UUID.randomUUID.toString
 
     val spark = SparkSession
       .builder
@@ -76,6 +83,7 @@ object StructuredKafkaWordCount {
     val query = wordCounts.writeStream
       .outputMode("complete")
       .format("console")
+      .option("checkpointLocation", checkpointLocation)
       .start()
 
     query.awaitTermination()