Do not override jar task's classifier if bootJar task does not interfere in Gradle

[chanseokoh]

In #2178, we overrode the archiveClassifier (classifier is deprecated) of the jar task, because by default both the jar and bootJar tasks write their respective JAR to the same location (build/<name>.jar). However, if bootJar is configured to write its fat JAR to a different location, there's no need to rename the original JAR generated by the jar task.

@ewirch

[ewirch]

Basically, if the classifier or archiveClassifier of bootJar is set, then make Jib not set the classifier of the jar task.

That would do the trick.

But, wouldn't it be cleaner to create a new 'jar' task, exclusively for jib? Then you wouldn't need to mess with the default 'jar' task.

[chanseokoh]

create a new 'jar' task, exclusively for jib

Looks like it's not easy to clone the jar task that guarantees to create the exact same jar file as the jar task will produce.

That said, I have refined the logic to be more conservative like this:

• If both bootJar and jar are enabled and their jar locations conflict, throw an error. This is really like a misconfiguration that the user needs to address.
• Set the classifier of jar to original only when all the followings are true.
  1. jar is disabled.
  2. bootJar is enabled.
  3. Their jar locations conflict.

[chanseokoh]

@ewirch we've release Jib 2.1.0 with this change. You may want to take a spin.