ClassLoaderXmlPreprocessor extracts a ClassLoader definition from the xml document, builds a class loader, assigns
the class loader to the application context and xml reader, and removes the classpath element from document.
Gets the ServiceNames of the services defined in the application context if the configuration has been started,
otherwise this method returns an empty set.
Extracts a ClassLoader definition from the xml document, builds a class loader, assigns
the class loader to the application context and xml reader, and removes the classpath element from document.