code: public static String getParentFolder(String resource) {
  
          if (CmsStringUtil.isEmptyOrWhitespaceOnly(resource) || "/".equals(resource)) {
              return null;
          }
          // remove the last char, for a folder this will be "/", for a file it does not matter
          String parent = (resource.substring(0, resource.length() - 1));
          // now as the name does not end with "/", check for the last "/" which is the parent folder name
          return parent.substring(0, parent.lastIndexOf('/') + 1);
      }
docs: Returns the absolute parent folder name of a resource.<p>
  
  The parent resource of a file is the folder of the file.
  The parent resource of a folder is the parent folder.
  The parent resource of the root folder is <code>null</code>.<p>
  
  Example: <code>/system/workplace/</code> has the parent <code>/system/</code>.
  
  @param resource the resource to find the parent folder for
  @return the calculated parent absolute folder path, or <code>null</code> for the root folder