build: change checkstyle to google code format, plus adding spotless

[aepfli]

We regularly fight with code styles in pull requests, which is annoying to both the contributors and the maintainers.

There are tools out there, like Spotless, that can automate those processes. We could define our code style, but there is already one widely used code style from Google (Google Java format).

Existing plugins help us follow this code style within IntelliJ and Visual Studio Code. Switching to this definition can improve the overall experience.

This supersedes the pull request with .editorconfig

notes

• first commit contains the changes to the tooling
• second commit contains the applied formatting changes

Disclaimer

This pull request should be used to discuss this; most people do not have significant opinions regarding code styles as long as there are tools to enforce them. Now we have a maven target, spotless:apply, which will inform you about violations and fix them.

relates to: https://github.com/open-feature/java-sdk-contrib/pull/1121/checks

[codecov]

Codecov Report

Attention: Patch coverage is 98.70968% with 2 lines in your changes missing coverage. Please review.

Project coverage is 93.69%. Comparing base (f1817d8) to head (09a46b9).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
...in/java/dev/openfeature/sdk/EvaluationContext.java	50.00%	0 Missing and 2 partials ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##               main    #1264      +/-   ##
============================================
+ Coverage     93.47%   93.69%   +0.21%     
  Complexity      464      464              
============================================
  Files            43       43              
  Lines          1088     1110      +22     
  Branches         86       89       +3     
============================================
+ Hits           1017     1040      +23     
+ Misses           44       43       -1     
  Partials         27       27              

Flag	Coverage Δ
unittests	93.69% <98.70%> (+0.21%)	⬆️

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[aepfli]

... added contributing.md section

[toddbaert]

open-feature/java-sdk-contrib#1121 (review)

[guidobrei]

Thank you for adding this.
Not sure if it should be part of this PR, but do we plan to check/autocorrect in pre-commit hooks and our CI pipeline?

[aepfli]

Thank you for adding this. Not sure if it should be part of this PR, but do we plan to check/autocorrect in pre-commit hooks and our CI pipeline?

actually this should be automatically part of maven verify - based on the docs By default, spotless:check is bound to verify maven phase. This means it is not required to explicitly bind the plugin execution, and the following will suffice; but within my demo pr #1265 - i do not see an execution

... but it seems like i accidentally bound it to the wrong profile, i will fix this

[aepfli]

added spotless:verify to the check goal now correctly, misread the docs here. thank you for pointing me into the right direction @guidobrei

[sonarqubecloud]

Quality Gate passed

Issues
47 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud