code: private boolean isExternal(String filename) {
  
          boolean external = false;
          if (filename.indexOf("://") > 0) {
              external = true;
          }
          return external;
      }
docs: Tests if a filename is an external name, that is this name does not point into the OpenCms VFS.<p>
  A filename is an external name if it contains the string "://", e.g. "http://" or "ftp://".<p>
  
  @param filename the filename to test
  
  @return true or false