返回要下载文件大小的方法

项目中用到的，忘记哪个网址找到的方法了，show：

 public int tryGetFileSize(URL url) {
        HttpURLConnection conn = null;
        try {
            conn = (HttpURLConnection) url.openConnection();
            conn.setRequestMethod("HEAD");
            conn.getInputStream();
            return conn.getContentLength();
        } catch (IOException e) {
            return -1;
        } finally {
            conn.disconnect();
        }
    }