code: private Iterable<URL> createServiceFileIterator() {
          if (classLoader == null) {
              ClassLoader classLoader = SchemaFactoryFinder.class.getClassLoader();
              return Collections.singleton(classLoader.getResource(SERVICE_ID));
          } else {
              try {
                  Enumeration<URL> e = classLoader.getResources(SERVICE_ID);
                  if (debug && !e.hasMoreElements()) {
                      debugPrintln("no "+SERVICE_ID+" file was found");
                  }
  
                  // wrap it into an Iterator.
                  return Collections.list(e);
              } catch (IOException e) {
                  if (debug) {
                      debugPrintln("failed to enumerate resources "+SERVICE_ID);
                      e.printStackTrace();
                  }
                  return Collections.emptySet();
              }
          }
      }
docs: Returns an {@link Iterator} that enumerates all
  the META-INF/services files that we care.