SonarQube Custom Java Checks

This project provides a few simple checks for Java to demonstrate the
implementation and use of custom rules in SonarQube.

• NullableReturnCheck - Shows an issue on INFO level to the developer
  suggesting to consider using java.util.Optional or io.vavr.control.Option
  instead of a potentially nullable return value. Implementation is done using
  the visitor pattern available in Sonar.
• NullnessAnnotationCheck - Forbids the use of any nullness annotations
  besides those of the Checker Framework. The
  rule itself is marked deprecated. There is a more generic approach
  available that does not require a custom rule --
  rule templates.
• VavrPublicSignatureCheck - Forbid the use of vavr.io
  classes in public API. This includes public/protected methods used in
  interfaces and abstract classes.

Check the setup page to
get a brief overview of how to install this plugin.

Known Issues

It seems that Sonar is not able to catch type annotations. Both the
NullnessAnnotationCheck as well as the OOTB template "Track uses of
disallowed classes" are not able to match the use of a forbidden annotation.