The metrics-logback13 and metrics-logback14 modules provide InstrumentedAppender,
a Logback Appender implementation which records the rate of logged events by their logging level.
You add it to the root logger programmatically:
final LoggerContext factory = (LoggerContext) LoggerFactory.getILoggerFactory();
final Logger root = factory.getLogger(Logger.ROOT_LOGGER_NAME);
final InstrumentedAppender metrics = new InstrumentedAppender(registry);
metrics.setContext(root.getLoggerContext());
metrics.start();
root.addAppender(metrics);