code: private InputStream openCustomSortOrderFile() throws FileNotFoundException {
          InputStream inputStream;
          try {
              inputStream = new FileInputStream(customSortOrderFile);
          } catch (FileNotFoundException ex) {
              // try classpath
              try {
                  URL resource = this.getClass().getClassLoader().getResource(customSortOrderFile);
                  if (resource == null) {
                      throw new IOException("Cannot find resource");
                  }
                  inputStream = resource.openStream();
              } catch (IOException e1) {
                  throw new FileNotFoundException(String.format("Could not find %s or %s in classpath", new File(
                          customSortOrderFile).getAbsolutePath(), customSortOrderFile));
              }
          }
          return inputStream;
      }
docs: Load custom sort order file from absolute or class path.
  
  @return a stream to the opened resource