context.go
func URLParam(r *http.Request, key string) string {
	if rctx := RouteContext(r.Context()); rctx != nil {
		return rctx.URLParam(key)
	}
	return ""
}
func URLParam(r *http.Request, key string) string {
	if rctx := RouteContext(r.Context()); rctx != nil {
		return rctx.URLParam(key)
	}
	return ""
}
// URLParam returns the url parameter from a http.Request object.