RSPEC-1312 - Loggers should be "private static final" and should share a naming convention

[yeikel]

Regardless of the logging framework in use (logback, log4j, commons-logging, java.util.logging, …​), loggers should be:

private: never be accessible outside of its parent class. If another class needs to log something, it should instantiate its own logger.
static: not be dependent on an instance of a class (an object). When logging something, contextual information can of course be provided in the messages but the logger should be created at class level to prevent creating a logger along with each object.
final: be created once and only once per class.

public Logger logger = LoggerFactory.getLogger(Foo.class);  // Noncompliant

private static final Logger LOGGER = LoggerFactory.getLogger(Foo.class);

See : https://rules.sonarsource.com/java/RSPEC-1312