[SPARK-21601][BUILD] Modify the pom.xml file, increase the maven compiler jdk attribute

[highfei2011]

What changes were proposed in this pull request?

When using maven to compile spark, I want to add a modified jdk property. This is user-friendly.

How was this patch tested?

mvn test

[AmplabJenkins]

Can one of the admins verify this patch?

[markhamstra]

These are maven-compiler-plugin configurations. We don't use maven-compiler-plugin to compile Java code: 74cda94

[highfei2011]

Ok,Thanks, @markhamstra .

[srowen]

@highfei2011 @markhamstra I think this is legit actually but for a different reason: https://issues.apache.org/jira/browse/SPARK-21605

[markhamstra]

Hmmm... that's arguably broken behavior on the part of IntelliJ or something to be worked around in IntelliJ configuration, not by hacking our POM. Without the POM hack, though, it is definitely something that deserves explanation in the Building Spark docs.

[srowen]

The Maven build is the build of reference, and we rely on IDEs to parse the details of the build from the pom.xml file. So it's right for the IDE to need to find information like JDK level (among a hundred other things) in the POM file. The maven-compiler-plugin is a standard built-in plugin whose config it consults to figure this out. It's not at all a hack. At least: we've always had this (and other superfluous config) for the compiler plugin in the build. This just cropped up because we trimmed it, and trimmed two lines too far.

[markhamstra]

Maven is the build of reference, true; but maven itself doesn't need the JDK version to be specified both in the scala plugin configuration and in the compiler plugin configuration. While I understand that IntelliJ is used by many Spark developers, it isn't some sort of officially preferred IDE of reference. That's why I have some qualms about embedding workarounds into our POM just to satisfy the idiosyncrasies of a particular IDE.

[srowen]

Sure, it really doesn't hurt, because we already define and maintain ${java.version} anyway. It's two lines of standard config that were already there. This is truly not an issue.

[markhamstra]

Yes, it doesn't really hurt anything except to be confusing cruft that has a tendency to accumulate in POMs. If we're going to put those lines back, I suggest that they be accompanied by a comment that they are known to be a useful assist for certain versions of IntelliJ and are not needed for the correctness of the build itself.

[highfei2011]

Hi, @srowen @markhamstra ,This problem has been solved，https://github.com/apache/spark/pull/18808