code: public static String getRfsPath(String filename, String extension, String parameters) {
  
          boolean appendSlash = false;
          if (filename.endsWith("/")) {
              appendSlash = true;
              filename = filename.substring(0, filename.length() - 1);
          }
          StringBuffer buf = new StringBuffer(128);
          buf.append(filename);
          buf.append('_');
          int h = parameters.hashCode();
          // ensure we do have a positive id value
          buf.append(h > 0 ? h : -h);
          buf.append(extension);
          if (appendSlash) {
              buf.append("/");
          }
          return buf.toString();
      }
docs: Creates unique, valid RFS name for the given filename that contains
  a coded version of the given parameters, with the given file extension appended.<p>
  
  Adapted from CmsFileUtil.getRfsPath().
  
  @param filename the base file name
  @param extension the extension to use
  @param parameters the parameters to code in the result file name
  
  @return a unique, valid RFS name for the given parameters
  
  @see org.opencms.staticexport.CmsStaticExportManager