code: public static String parseUrl(String urlStr, String partToExtract, String key) {
  		if (!"QUERY".equals(partToExtract)) {
  			return null;
  		}
  
  		String query = parseUrl(urlStr, partToExtract);
  		if (query == null) {
  			return null;
  		}
  
  		Pattern p = Pattern.compile("(&|^)" + Pattern.quote(key) + "=([^&]*)");
  		Matcher m = p.matcher(query);
  		if (m.find()) {
  			return m.group(2);
  		}
  		return null;
  	}
docs: Parse url and return various parameter of the URL.
  If accept any null arguments, return null.
  
  @param urlStr        URL string.
  @param partToExtract must be QUERY, or return null.
  @param key           parameter name.
  @return target value.