开发语言：Java
开发生态：Android

一、申请权限

在清单AndroidManifest.xml中添加

  <!-- 访问网络状态-->
  <uses-permission android:name="android.permission.INTERNET" />

二、功能实现

  /**
   * 获取网络资源文件大小
   */
  private void getNetworkFileSize() {
    final Handler handler = new Handler(Looper.myLooper()) {
      @Override
      public void handleMessage(Message msg) {
        String fileSize = msg.getData().getString("fileSize");
        Log.d("fileSize", fileSize);
      }
    };

   String fileUrl = call.argument("fileUrl");

    if (fileUrl == null) {
      return;
    }

    if (fileUrl.length() == 0) {
      return;
    }

    URL url = null;
    try {
      url = new URL(fileUrl);
    } catch (MalformedURLException e) {
      e.printStackTrace();
    }

    if (url == null) {
      return;
    }

    final URL finalUrl = url;
    new Thread(new Runnable() {
      @Override
      public void run() {
        try {
          HttpURLConnection urlConnection = (HttpURLConnection) finalUrl.openConnection();
          int fileLength = urlConnection.getContentLength();

          Bundle bundle = new Bundle();
          bundle.putString("fileSize", "文件大小：" + formatFileSize(fileLength));

          Message message = handler.obtainMessage();
          message.setData(bundle);

          handler.sendMessage(message);
        } catch (IOException e) {
          e.printStackTrace();
        }
      }
    }).start();
  }

  /**
   * 转换文件大小
   * 
   * @param fileS
   * @return
   */
  public static String formatFileSize(int fileS) {
    DecimalFormat df = new DecimalFormat("#.00");
    String fileSizeString;
    String wrongSize = "0B";

    if (fileS == 0) {
      return wrongSize;
    }

    if (fileS < 1024) {
      fileSizeString = df.format((double) fileS) + "B";
    } else if (fileS < 1024 * 1024) {
      fileSizeString = df.format((double) fileS / 1024) + "KB";
    } else if (fileS < 1024 * 1024 * 1024) {
      fileSizeString = df.format((double) fileS / (1024 * 1024)) + "MB";
    } else {
      fileSizeString = df.format((double) fileS / (1024 * 1024 * 1024)) + "GB";
    }

    return fileSizeString;
  }

小白的进阶之路，感谢大家的支持！