A端应用比较多，B端几乎没有需求，contentLength根据选用框架不同，写法会有不同，这里是okhttp的写法。
public static void copy(Response response, OutputStream os) throws IOException { InputStream is = response.body().byteStream(); long total = response.body().contentLength(); long cnt = 0; int len; byte[] buf = new byte[4096]; while ((len = is.read(buf)) != -1) { os.write(buf, 0, len); cnt += len; int progress = (int) (cnt * 1.0f / total * 100); //TODO:进度回调 } os.flush(); }
