Returns the names of all registered extractors, sorted alphabetically.
Returns an ExtractorGroup containing the ExtractorFactory mathing the names provided as input.
factory - an ExtractorFactory to register.
IllegalArgumentException - if trying to register a ExtractorFactory that already exists in the registry.
IllegalArgumentException - If there is not an ExtractorFactory associated to the provided name.
An ExtractorGroup with all the registered Extractor.
names - A List containing the names of the desired ExtractorFactory.
true if is there a ExtractorFactory associated to the provided name.