code: public static final void useSl4jLoggers() {
  		String name = LoggerFactory.class.getName();
  		LoggerFactory loggerFactory = new Slf4JLoggerFactory();
  		loggerFactory.getLogger(name).debug("Using Slf4j logging framework");
  		LOGGER_FACTORY = loggerFactory;
  	}
docs: Force the usage of SL4J-based {@link Logger Loggers}, throwing an exception if
  SLF4J isn't available on the classpath. Prefer using {@link #resetLoggerFactory()}
  as it will fallback in the later case.
  <p>
  The previously active logger factory is simply replaced without
  any particular clean-up.