[java] Add support for exclusions to a few rules

[nkavian]

Is your feature request related to a problem? Please describe.
Example: I want to enforce a minimum length of 4 for ShortClassName, ShortMethodName, ShortVariable, but my project has a few exceptions. I do not want:

• to disable the rule,
• to lower the minimum,
• to use // NOPMD in so many places

Describe the solution you'd like
I'd like support for an exclusions parameter similar to FieldNamingConventions where exceptions to the rule can be provided.

Describe alternatives you've considered
I've lowered my minimum to 2 until this can be addressed.

Additional context
PMD is awesome.

[jsotuyod]

Are you looking to ignore complete files or to whitelist some specific short names for the whole codebase?

I believe that ignoring complete files could be useful at a base-rule level (and could help to bring PMD into pre-existing codebases), but if you want to whitelist any method called or regardless of the class it is in, then this wouldn't suffice.

[nkavian]

Correct, specific method names across the code base. Sorry if my description wasn't clear. It was crystal clear in my mind when I wrote it, lol.

I'm looking for the same behavior of exclusions on FieldNamingConventions, to be applied to the other 3 rules.

[adamhibbert]

I'd like to do the same, for instance 'id' as a variable is common in my codebase, but I'd like to set ShortVariable minimum to 3, but have had to reduce it to 2 to get around this.