[Spike] Try out Spotless; outcome: Do include Spotless in the project

[jwlibby]

Try out Spotless and see what you think. When evaluating refer to the questions in #462 and upon completion add your pros and cons for this plugin as a comment to the aforementioned story. Plugin link: Spotless.

Considerations for implementation cards:

• Gradle: easy
• Maven: lots of challenges, dependencies: Plexus, SLF4J, Kotlin, Eclipse; the plugin dependency wants Sonatype rather than Maven Central also easy. The challenges and dependencies issues mentioned were because I had incorrectly added the plugin as a dependency, not as a plugin

Related: #534 for epic on dependency management.

[jwlibby]

• Does the plugin work with both Gradle and Maven? Yes (also works with SBT)
• How does this mesh with Checkstyle? Or can the plugin replace Checkstyle? It can replace it, it is the same plus more functionality
• Can the plugin automatically reformat the code as part of the local build process? yes
• If code is reformatted before pushing, how will the programmer be aware of this? we would manually set a step to log that such happened to the console
• Does the plugin have good backward/forward compatibility and adaptability to different versions of the language, its dependencies and the runtime environment (jvm)? for java I think so since java itself is backwards compatible. Plus there is an attribute to format according to a particular java version
• Is the plugin configurable in its rules to meet my team standards? compare to what is in checkstyle configuration
• Should the book recommend a "one true" formatting style, provide a list of common styles, or leave that up to each team? No
• Book tries to be agnostic on most things. An existing example is the checkstyle settings in config/checkstyle/*. not sure ab this question

[jwlibby]

spike can be found in spotless-spike branch

[binkley]

Note: the spotless-spike branch has a mistake in using Spotless as a dependency rather than a plugin.

[binkley]

@jwlibby The only feedback I have on the writing is this:

* [Spotless](https://github.com/diffplug/spotless) — Focus on Google style guides for Java.

I'm unsure what style to suggest here. For example, I noticed the Google style includes the "AOSP" variant that uses 4-space indentation rather than Google's odd 2-space indentation. Palantir is also an interesting choice.

So perhaps soften the language to not offer a recommendation on style choice.