[SPARK-15031][EXAMPLE] Use SparkSession in Scala/Python/Java example.

## What changes were proposed in this pull request?

This PR aims to update Scala/Python/Java examples by replacing `SQLContext` with newly added `SparkSession`.

- Use **SparkSession Builder Pattern** in 154(Scala 55, Java 52, Python 47) files.
- Add `getConf` in Python SparkContext class: `python/pyspark/context.py`
- Replace **SQLContext Singleton Pattern** with **SparkSession Singleton Pattern**:
  - `SqlNetworkWordCount.scala`
  - `JavaSqlNetworkWordCount.java`
  - `sql_network_wordcount.py`

Now, `SQLContexts` are used only in R examples and the following two Python examples. The python examples are untouched in this PR since it already fails some unknown issue.
- `simple_params_example.py`
- `aft_survival_regression.py`

## How was this patch tested?

Manual.

Author: Dongjoon Hyun <dongjoon@apache.org>

Closes #12809 from dongjoon-hyun/SPARK-15031.

1 files changed, 10 insertions, 9 deletions

diff --git a/examples/src/main/python/streaming/sql_network_wordcount.py b/examples/src/main/python/streaming/sql_network_wordcount.py
index 1ba5e9fb78..588cbfee14 100644
--- a/examples/src/main/python/streaming/sql_network_wordcount.py
+++ b/examples/src/main/python/streaming/sql_network_wordcount.py
@@ -33,13 +33,14 @@ import sys
 
 from pyspark import SparkContext
 from pyspark.streaming import StreamingContext
-from pyspark.sql import SQLContext, Row
+from pyspark.sql import Row, SparkSession
 
 
-def getSqlContextInstance(sparkContext):
-    if ('sqlContextSingletonInstance' not in globals()):
-        globals()['sqlContextSingletonInstance'] = SQLContext(sparkContext)
-    return globals()['sqlContextSingletonInstance']
+def getSparkSessionInstance(sparkConf):
+    if ('sparkSessionSingletonInstance' not in globals()):
+        globals()['sparkSessionSingletonInstance'] =\
+            SparkSession.builder.config(conf=sparkConf).getOrCreate()
+    return globals()['sparkSessionSingletonInstance']
 
 
 if __name__ == "__main__":
@@ -60,19 +61,19 @@ if __name__ == "__main__":
         print("========= %s =========" % str(time))
 
         try:
-            # Get the singleton instance of SQLContext
-            sqlContext = getSqlContextInstance(rdd.context)
+            # Get the singleton instance of SparkSession
+            spark = getSparkSessionInstance(rdd.context.getConf())
 
             # Convert RDD[String] to RDD[Row] to DataFrame
             rowRdd = rdd.map(lambda w: Row(word=w))
-            wordsDataFrame = sqlContext.createDataFrame(rowRdd)
+            wordsDataFrame = spark.createDataFrame(rowRdd)
 
             # Register as table
             wordsDataFrame.registerTempTable("words")
 
             # Do word count on table using SQL and print it
             wordCountsDataFrame = \
-                sqlContext.sql("select word, count(*) as total from words group by word")
+                spark.sql("select word, count(*) as total from words group by word")
             wordCountsDataFrame.show()
         except:
             pass