code: private static void handleSingletonClass(String key, String value) throws Exception {
          Object object = handleValue(value);
          if(key.contains(",")) {
              String[] interfaces = key.split(",");
              for (String anInterface : interfaces) {
                  serviceMap.put(anInterface, object);
              }
          } else {
              serviceMap.put(key, object);
          }
      }
docs: For each singleton definition, create object with the initializer class and method,
  and push it into the service map with the key of the class name.
  
  @param key String class name of the object that needs to be initialized
  @param value String class name of initializer class and method separated by "::"
  @throws Exception exception thrown from the object creation