public Logger getLogger(String name) {
        // the root logger is called "" in JUL
        if (name.equalsIgnoreCase(Logger.ROOT_LOGGER_NAME)) {
            name = JUL_ROOT_LOGGER_NAME;
        }

        Logger slf4jLogger = loggerMap.get(name);
        if (slf4jLogger != null)
            return slf4jLogger;
        else {
            java.util.logging.Logger julLogger = java.util.logging.Logger.getLogger(name);
            Logger newInstance = new JDK14LoggerAdapter(julLogger);
            Logger oldInstance = loggerMap.putIfAbsent(name, newInstance);
            return oldInstance == null ? newInstance : oldInstance;
        }
    }
the root logger is called "" in JUL
slf4j-jdk14/src/main/java/org/slf4j/jul/JDK14LoggerFactory.java