code: @Nullable
    private static String getBuildDate() {
      try {
        URL res = JLanguageTool.class.getResource(JLanguageTool.class.getSimpleName() + ".class");
        if (res == null) {
          // this will happen on Android, see http://stackoverflow.com/questions/15371274/
          return null;
        }
        Object connObj = res.openConnection();
        if (connObj instanceof JarURLConnection) {
          JarURLConnection conn = (JarURLConnection) connObj;
          Manifest manifest = conn.getManifest();
          return manifest.getMainAttributes().getValue("Implementation-Date");
        } else {
          return null;
        }
      } catch (IOException e) {
        throw new RuntimeException("Could not get build date from JAR", e);
      }
    }
docs: Returns the build date or {@code null} if not run from JAR.