NIFI-4864: Improvements to PR #2470

[zenfenan]

The original PR #2470 had an unhandled situation wherein the components that don't have any PropertyDescriptor marked as dynamicallyModifiesClasspath(true) won't have the additionalResourcesFingerprint set i.e. it will be null so the framework will attempt to reload the resources. This caused an unexpected scenario especially when using Schema Registry services which @bbende explained in the Release Apache NiFi 1.6.0 Dev thread

I have tested both the scenarios:

1. The actual reason why this ticket was raised i.e. to smartly reload newly added additional resources, upon the component's start and stop

2. The unhandled situation that is mentioned above (schema registry situation)

---

Thank you for submitting a contribution to Apache NiFi.

In order to streamline the review of the contribution we ask you
to ensure the following steps have been taken:

For all changes:

• Is there a JIRA ticket associated with this PR? Is it referenced
  in the commit message?

• Does your PR title start with NIFI-XXXX where XXXX is the JIRA number you are trying to resolve? Pay particular attention to the hyphen "-" character.

• Has your PR been rebased against the latest commit within the target branch (typically master)?

• Is your initial contribution a single, squashed commit?

For code changes:

• Have you ensured that the full suite of tests is executed via mvn -Pcontrib-check clean install at the root nifi folder?
• Have you written or updated unit tests to verify your changes?
• If adding new dependencies to the code, are these dependencies licensed in a way that is compatible for inclusion under ASF 2.0?
• If applicable, have you updated the LICENSE file, including the main LICENSE file under nifi-assembly?
• If applicable, have you updated the NOTICE file, including the main NOTICE file found under nifi-assembly?
• If adding new Properties, have you added .displayName in addition to .name (programmatic access) for each of the new properties?

For documentation related changes:

• Have you ensured that format looks appropriate for the output in which it is rendered?

Note:

Please ensure that once the PR is submitted, you check travis-ci for build issues and submit an update to your PR as soon as possible.

[ottobackwards]

Travis is failing with a check style error. I can't see the actual error though. Also, I don't see a check style configuration in the project, so I can't set it up locally to check it out. Is there a check style configuration?

[zenfenan]

My bad. I'm using nifi-checkstyle.xml but some recent updates on my IDE messed it up. It's trailing white lines codestyle error. Will rebase.

[ottobackwards]

so nifi has a check style, but it isn't in the repo?

[bbende]

It's in the root pom as part of the plugin... the contrib-check Maven profile enables checkstyle and RAT checks, this is what Travis is doing.

[ottobackwards]

thanks @bbende, so using the check style referenced with the idea will work? Is that what you all do?

[bbende]

Not sure what others do, but I can't remember doing anything in my IDE (IntelliJ) other than changing the new Java class template to have the Apache License at the top by default.

I just run mvn clean install -Pcontrib-check before submitting a PR. If I changed code all over the place then I run it from the root, or if I was working in a single module then I run inside that module.

I think most standard Java styling passes the check-style, almost every time I have a failure it is from an unused import.

[ottobackwards]

Thanks @bbende, I have multiple check styles since different apache projects have different settings so I try to be explicit per project

[bbende]

This looks good, verified it resolves the issue and is no longer reloading any components except those that have the classpath property descriptors, going to merge