code: @Pure
  	public static URL getJarURL(URL url) {
  		if (!isJarURL(url)) {
  			return null;
  		}
  		String path = url.getPath();
  		final int idx = path.lastIndexOf(JAR_URL_FILE_ROOT);
  		if (idx >= 0) {
  			path = path.substring(0, idx);
  		}
  		try {
  			return new URL(path);
  		} catch (MalformedURLException exception) {
  			return null;
  		}
  	}
docs: Replies the jar part of the jar-scheme URL.
  
  <p>If the input URL is {@code jar:file:/path1/archive.jar!/path2/file},
  the output of this function is {@code file:/path1/archive.jar}.
  
  @param url the URL to test.
  @return the URL of the jar file in the given URL, or <code>null</code>
  if the given URL does not use jar scheme.