获取图片，文件大小

    // okHttpClient 实例
    OkHttpClient okHttpClient = new OkHttpClient();
    // 定义一个request
    Request request = new Request.Builder().url(url).build();
    try {
      // 执行请求
      Response response = okHttpClient.newCall(request).execute();
      byte[] bytes =response.body().bytes();
      System.out.println("大小为： " +bytes.length + " 字节");
    } catch (IOException e) {
      // 抓取异常
      System.out.println("request " + url + " error . ");
      e.printStackTrace();
    }