怎样计算下载速度？解决方案

            URL url = new URL(urls);            URLConnection conn = url.openConnection();            conn.connect();            System.out.println(urls + " 长度：" + conn.getContentLength() / 1024 + "KB");            InputStream fis = conn.getInputStream();            long a = System.currentTimeMillis();            FileOutputStream out = new FileOutputStream(path);            byte buf[] = new byte[10240];            int n;            while ((n = fis.read(buf)) != -1) {                out.write(buf, 0, n);            }            fis.close();            out.close();            long b = System.currentTimeMillis();            System.out.println("[+]: 下载费时："+ String.valueOf(b-a) + "毫秒");