code: public Set<String> catalogNames() {
  		Set<String> catalogs = new HashSet<>();
  		for (ResourceSelection selection : selections) {
  			catalogs.add(selection.getCatalog());
  		}
  		return catalogs;
  	}
docs: 汇总得到所有资源仓库选择的类别信息。
  
  @return 类别名称集合