see more from https://github.com/openzipkin/brave/issues/867, also see https://github.com/apache/incubator-dubbo/issues/3576
public void setFuture(Future<?> future) {
        this.future = future;
    }
    public List<URL> getUrls() {
        return urls == null && url != null ? (List<URL>) Arrays.asList(url) : urls;
    }
    public void setUrls(List<URL> urls) {
        this.urls = urls;
    }
    public URL getUrl() {
        return url;
    }
    public void setUrl(URL url) {
        this.url = url;
    }
    /**
     * get method name.
     *
     * @return method name.
     */
    public String getMethodName() {
        return methodName;
    }
    public void setMethodName(String methodName) {
        this.methodName = methodName;
    }
    /**
     * get parameter types.
     *
     * @serial