[SPARK-17374][SQL] Better error messages when parsing JSON using DataFrameReader

[clockfly]

What changes were proposed in this pull request?

This PR adds better error messages for malformed record when reading a JSON file using DataFrameReader.

For example, for query:

import org.apache.spark.sql.types._
val corruptRecords = spark.sparkContext.parallelize("""{"a":{, b:3}""" :: Nil)
val schema = StructType(StructField("a", StringType, true) :: Nil)
val jsonDF = spark.read.schema(schema).json(corruptRecords)

Before change:
We silently replace corrupted line with null

scala> jsonDF.show
+----+
|   a|
+----+
|null|
+----+

After change:
Add an explicit warning message:

scala> jsonDF.show
16/09/02 14:43:16 WARN JacksonParser: Found at least one malformed records (sample: {"a":{, b:3}). The JSON reader will replace
all malformed records with placeholder null in current PERMISSIVE parser mode.
To find out which corrupted records have been replaced with null, please use the
default inferred schema instead of providing a custom schema.

Code example to print all malformed records (scala):
===================================================
// The corrupted record exists in column _corrupt_record.
val parsedJson = spark.read.json("/path/to/json/file/test.json")

+----+
|   a|
+----+
|null|
+----+

How was this patch tested?

Unit test.

[SparkQA]

Test build #64818 has finished for PR 14929 at commit 50e312f.

• This patch passes all tests.
• This patch merges cleanly.
• This patch adds no public classes.

[SparkQA]

Test build #64821 has finished for PR 14929 at commit 3491f15.

• This patch passes all tests.
• This patch merges cleanly.
• This patch adds no public classes.

[clockfly]

Only print a warning for the first time.

[clockfly]

@cloud-fan

[cloud-fan]

private[this]?

[SparkQA]

Test build #64838 has finished for PR 14929 at commit b7ebf26.

• This patch fails Spark unit tests.
• This patch merges cleanly.
• This patch adds no public classes.

[SparkQA]

Test build #64841 has finished for PR 14929 at commit 82f9927.

• This patch fails Spark unit tests.
• This patch merges cleanly.
• This patch adds no public classes.

[SparkQA]

Test build #64955 has finished for PR 14929 at commit f47f921.

• This patch fails Spark unit tests.
• This patch merges cleanly.
• This patch adds no public classes.

[clockfly]

retest this please

[SparkQA]

Test build #64996 has finished for PR 14929 at commit f47f921.

• This patch passes all tests.
• This patch merges cleanly.
• This patch adds no public classes.

[cloud-fan]

why create this temp view? we can

checkAnswer(jsonDF.select($"a", $"b", $"c"), Seq(Row...))

[cloud-fan]

thanks, merging to master! @clockfly can you send a follow-up PR to address the minor comment in test?