Java下载进度

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();
}