java 通过url获取文件大小

1：目的 ：在不下载文件的前提下，通过http head 请求，获取一个文件的大小；

2：具体代码方法如下：

/**    * 获取网络文件大小     */    private static long getFileLength(String downloadUrl) throws IOException{  if(downloadUrl == null || "".equals(downloadUrl)){  return 0L ;   }      URL url = new URL(downloadUrl);      HttpURLConnection conn = null;      try {          conn = (HttpURLConnection) url.openConnection();          conn.setRequestMethod("HEAD");          conn.setRequestProperty("User-Agent", "Mozilla/5.0 (Windows 7; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/47.0.2526.73 Safari/537.36 YNoteCef/5.8.0.1 (Windows)");          return (long) conn.getContentLength();      } catch (IOException e) {          return 0L;      } finally {          conn.disconnect();    }     }