code: public String getPara(int index) {
  		if (index < 0)
  			return getPara();
  		
  		if (urlParaArray == null) {
  			if (urlPara == null || "".equals(urlPara))	// urlPara maybe is "" see ActionMapping.getAction(String)
  				urlParaArray = NULL_URL_PARA_ARRAY;
  			else
  				urlParaArray = urlPara.split(URL_PARA_SEPARATOR);
  			
  			for (int i=0; i<urlParaArray.length; i++)
  				if ("".equals(urlParaArray[i]))
  					urlParaArray[i] = null;
  		}
  		return urlParaArray.length > index ? urlParaArray[index] : null;
  	}
docs: Get para from url. The index of first url para is 0.