[SPARK-4881][Minor] Use SparkConf#getBoolean instead of get().toBoolean

[sarutak]

It's really a minor issue.

In ApplicationMaster, there is code like as follows.

val preserveFiles = sparkConf.get("spark.yarn.preserve.staging.files", "false").toBoolean

I think, the code can be simplified like as follows.

val preserveFiles = sparkConf.getBoolean("spark.yarn.preserve.staging.files", false)

[SparkQA]

Test build #24578 has finished for PR 3733 at commit c63daa0.

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

[JoshRosen]

There are a couple of other instances of the same issue; do you think we can fix those, too?

[sarutak]

@JoshRosen I investigate how many code like SparkConf#get(..., "true/false").toBoolean by simple commands find . -name src -type d -exec grep -r '\.get(.*).*\.toBoolean' {} \; and I found following files have that issue .
I didn't investigate for HiveConf or SQLConf because those classes don't have getBoolean method.

• HadoopRDD.scala
• ApplicationMaster.scala
• SecurityManager.scala
• ClientBase.scala

Just only 4 files but it's really minor issue, so if you don't think it's needed to fix, I'l close this PR. Thanks!

[andrewor14]

No worries. Once you make those changes I will merge this. By the way for issues as minor as this one I don't think filing a JIRA is necessary. I would just put [Minor] in the title

[sarutak]

@andrewor14 Thanks for your notifidation. I keep in mind what you mentioned.

[JoshRosen]

LGTM; I'll pull this in as soon as Jenkins finishes. Thanks!

[SparkQA]

Test build #24750 has finished for PR 3733 at commit 0b5e4c9.

• This patch fails to build.
• This patch merges cleanly.
• This patch adds no public classes.

[SparkQA]

Test build #24752 has finished for PR 3733 at commit 1771430.

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

[JoshRosen]

I've merged this into master (1.3.0). Thanks!