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
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.
Noncompliant Code Example
With a default regular expression of
public Logger logger = LoggerFactory.getLogger(Foo.class); // Noncompliant
private static final Logger LOGGER = LoggerFactory.getLogger(Foo.class);
Variables of type
org.apache.maven.plugin.logging.Log are ignored.