[SPARK-16294][SQL] Labelling support for the include_example Jekyll plugin

## What changes were proposed in this pull request?

This PR adds labelling support for the `include_example` Jekyll plugin, so that we may split a single source file into multiple line blocks with different labels, and include them in multiple code snippets in the generated HTML page.

## How was this patch tested?

Manually tested.

<img width="923" alt="screenshot at jun 29 19-53-21" src="https://cloud.githubusercontent.com/assets/230655/16451099/66a76db2-3e33-11e6-84fb-63104c2f0688.png">

Author: Cheng Lian <lian@databricks.com>

Closes #13972 from liancheng/include-example-with-labels.

3 files changed, 18 insertions, 2 deletions

diff --git a/examples/src/main/java/org/apache/spark/examples/sql/JavaSparkSQL.java b/examples/src/main/java/org/apache/spark/examples/sql/JavaSparkSQL.java
index e512979ac7..7fc6c007b6 100644
--- a/examples/src/main/java/org/apache/spark/examples/sql/JavaSparkSQL.java
+++ b/examples/src/main/java/org/apache/spark/examples/sql/JavaSparkSQL.java
@@ -26,7 +26,9 @@ import org.apache.spark.api.java.function.Function;
 
 import org.apache.spark.sql.Dataset;
 import org.apache.spark.sql.Row;
+// $example on:init_session$
 import org.apache.spark.sql.SparkSession;
+// $example off:init_session$
 
 public class JavaSparkSQL {
   public static class Person implements Serializable {
@@ -51,10 +53,13 @@ public class JavaSparkSQL {
   }
 
   public static void main(String[] args) throws Exception {
+    // $example on:init_session$
     SparkSession spark = SparkSession
       .builder()
       .appName("JavaSparkSQL")
+      .config("spark.some.config.option", "some-value")
       .getOrCreate();
+    // $example off:init_session$
 
     System.out.println("=== Data source: RDD ===");
     // Load a text file and convert each line to a Java Bean.
diff --git a/examples/src/main/python/sql.py b/examples/src/main/python/sql.py
index ac7246938d..ea11d2c4c7 100644
--- a/examples/src/main/python/sql.py
+++ b/examples/src/main/python/sql.py
@@ -20,15 +20,20 @@ from __future__ import print_function
 import os
 import sys
 
+# $example on:init_session$
 from pyspark.sql import SparkSession
+# $example off:init_session$
 from pyspark.sql.types import Row, StructField, StructType, StringType, IntegerType
 
 
 if __name__ == "__main__":
+    # $example on:init_session$
     spark = SparkSession\
         .builder\
         .appName("PythonSQL")\
+        .config("spark.some.config.option", "some-value")\
         .getOrCreate()
+    # $example off:init_session$
 
     # A list of Rows. Infer schema from the first row, create a DataFrame and print the schema
     rows = [Row(name="John", age=19), Row(name="Smith", age=23), Row(name="Sarah", age=18)]
diff --git a/examples/src/main/scala/org/apache/spark/examples/sql/RDDRelation.scala b/examples/src/main/scala/org/apache/spark/examples/sql/RDDRelation.scala
index 1b019fbb51..deaa9f252b 100644
--- a/examples/src/main/scala/org/apache/spark/examples/sql/RDDRelation.scala
+++ b/examples/src/main/scala/org/apache/spark/examples/sql/RDDRelation.scala
@@ -18,7 +18,10 @@
 // scalastyle:off println
 package org.apache.spark.examples.sql
 
-import org.apache.spark.sql.{SaveMode, SparkSession}
+import org.apache.spark.sql.SaveMode
+// $example on:init_session$
+import org.apache.spark.sql.SparkSession
+// $example off:init_session$
 
 // One method for defining the schema of an RDD is to make a case class with the desired column
 // names and types.
@@ -26,13 +29,16 @@ case class Record(key: Int, value: String)
 
 object RDDRelation {
   def main(args: Array[String]) {
+    // $example on:init_session$
     val spark = SparkSession
       .builder
-      .appName("RDDRelation")
+      .appName("Spark Examples")
+      .config("spark.some.config.option", "some-value")
       .getOrCreate()
 
     // Importing the SparkSession gives access to all the SQL functions and implicit conversions.
     import spark.implicits._
+    // $example off:init_session$
 
     val df = spark.createDataFrame((1 to 100).map(i => Record(i, s"val_$i")))
     // Any RDD containing case classes can be used to create a temporary view.  The schema of the