code: private static URL getClassPathURL(String resourceName, URL resourceURL) {
      try {
        if ("file".equals(resourceURL.getProtocol())) {
          String path = resourceURL.getFile();
          // Compute the directory container the class.
          int endIdx = path.length() - resourceName.length();
          if (endIdx > 1) {
            // If it is not the root directory, return the end index to remove the trailing '/'.
            endIdx--;
          }
          return new URL("file", "", -1, path.substring(0, endIdx));
        }
        if ("jar".equals(resourceURL.getProtocol())) {
          String path = resourceURL.getFile();
          return URI.create(path.substring(0, path.indexOf("!/"))).toURL();
        }
      } catch (MalformedURLException e) {
        throw Throwables.propagate(e);
      }
      throw new IllegalStateException("Unsupported class URL: " + resourceURL);
    }
docs: Find the classpath that contains the given resource.