code: protected String getResourceBase() {
          if (useEmbeddedWebroot) { // option
              final String path = WEBROOT_RESOURCE_PATH;
              final URL webroot = getClass().getResource(path);
              if (webroot == null) {
                  throw new IllegalStateException("Not found the webroot resource: path=" + path);
              }
              try {
                  return webroot.toURI().toASCIIString();
              } catch (URISyntaxException e) {
                  throw new IllegalStateException("Illegal URL: " + webroot, e);
              }
          } else { // default is here
              return deriveWebappDir().getPath();
          }
      }
docs: -------------