[SPARK-26563]Fix java SimpleApp documentation

[LeoColman]

As is, the example provided by the documentation will crash with org.apache.spark.SparkException: A master URL must be set in your configuration. This error happens due to no Spark Master being configured.

When creating a spark master locally, the simple application works correctly, as This StackOverflow Answer will state.

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This change is very important as the original example will not work without this.

[AmplabJenkins]

Can one of the admins verify this patch?

[HyukjinKwon]

Master is specified in the submit in the example. then use the spark-submit script to run our program.

# Use spark-submit to run your application
$ YOUR_SPARK_HOME/bin/spark-submit \
  --class "SimpleApp" \
  --master local[4] \
  target/scala-2.11/simple-project_2.11-1.0.jar

That's also explain in the stack overflow link you pointed out:

To be clear, this is not what you should do in a production environment. In a production environment, spark.master should be specified in one of a couple other places: either in $SPARK_HOME/conf/spark-defaults.conf (this is where cloudera manager will put it), or on the command line when you submit the app. (ex spark-submit --master yarn).

[dongjoon-hyun]

+1 for @HyukjinKwon comment.

[LeoColman]

I do see that, and I did understand.

However, as I understand, a self-contained application should run by itself. As this is a hello world/quickstart application, I understood it as a lock-n-load, ready to execute.

Without configuring it (the way it's done in this commit), it's not possible to execute it without also having Spark installed. In my opinion, this violates the self-contained application definition.

If I'm thinking in the wrong way, please let me know

[LeoColman]

Maybe I misunderstood the documentation.
I have to confess that this is my first time fiddling with Apache Spark, and I got confused while trying to execute my Hello World application. When I figured it out, I thought that maybe I could prevent this in the future

[HyukjinKwon]

That's okay because it's clearly documented. I think I see no issue for following the documentation.

[dongjoon-hyun]

Thank you for understanding, @Kerooker .
No problem at all. I'm looking forward to seeing you in another PR.
For now, let me close this PR.