request 取得contextpath 和 config取得contextpath有什么区别

    public ActionMapping getActionMapping(HttpServletRequest request){
        String requestURI = request.getRequestURI();
        String str=request.getContextPath();
        String contextPath = config.getServletContext().getContextPath();
        System.out.println(str);
        System.out.println(contextPath);
        String actionName = requestURI.substring(contextPath.length()+1, requestURI.lastIndexOf("."));
        ActionMapping actionMapping = ActionManager.mappings.get(actionName);
        return actionMapping;
    }