code: public static <T> ExtensionLoader<T> getExtensionLoader(Class<T> clazz, ExtensionLoaderListener<T> listener) {
          ExtensionLoader<T> loader = LOADER_MAP.get(clazz);
          if (loader == null) {
              synchronized (ExtensionLoaderFactory.class) {
                  loader = LOADER_MAP.get(clazz);
                  if (loader == null) {
                      loader = new ExtensionLoader<T>(clazz, listener);
                      LOADER_MAP.put(clazz, loader);
                  }
              }
          }
          return loader;
      }
docs: Get extension loader by extensible class with listener
  
  @param clazz    Extensible class
  @param listener Listener of ExtensionLoader
  @param <T>      Class
  @return ExtensionLoader of this class