java判断服务器上的文件是否存在

   URL url = new URL("http://localhost:8080/image/sample/M-111.png");
   HttpURLConnection urlcon = (HttpURLConnection) url.openConnection();
   
   String message = urlcon.getHeaderField(0);
   int responseCode = urlcon.getResponseCode();
   String responseMessage = urlcon.getResponseMessage();
   System.out.println(message);
   System.out.println(responseCode);
   System.out.println(responseMessage);

如果文件存在：

HTTP/1.1 200 OK
200
OK
如果文件不存在：

HTTP/1.1 404 Not Found
404
Not Found