code: public Resource getResource(final ResourceSelection selection) {
  		String catalog = selection.getCatalog();
  		String version = selection.getVersion();
  		String name = selection.getName();
  		if (version == null) {
  			if (name == null) {
  				return getResource(catalog);
  			} else {
  				return getResource(catalog, name);
  			}
  		} else {
  			return repository.getResource(selection);
  		}
  	}
docs: 定位资源。
  
  @param selection
  资源选择
  @return 资源