private static void safelyInstantiate(List<SLF4JServiceProvider> providerList, Iterator<SLF4JServiceProvider> iterator) {
        try {
            SLF4JServiceProvider provider = iterator.next();
            providerList.add(provider);
        } catch (ServiceConfigurationError e) {
            Reporter.error("A service provider failed to instantiate:\n" + e.getMessage());
        }
    }
System property for explicitly setting the provider class. If set and the provider could be instantiated,
then the service loading mechanism will be bypassed.

@since 2.0.9
slf4j-api/src/main/java/org/slf4j/LoggerFactory.java