透过httpurlconnection获取服务器端的inputstream为什么会是空的呢

public static String requestPost(String linkAddress, int timeout) {
  String result = null;
  try {
   URL url = new URL(linkAddress); 
   setProxy();
   HttpURLConnection conn = (HttpURLConnection) url.openConnection();
   conn.setConnectTimeout(timeout * 1000);
   conn.connect();
   int state = conn.getResponseCode();
   System.out.println(state);
   System.out.println(linkAddress);
   if (state == HttpURLConnection.HTTP_OK) {
    InputStream in = conn.getInputStream();
    System.out.println("$$$$$$"+in.available());
    BufferedReader reader = new BufferedReader(new InputStreamReader(in, HTTP.UTF_8));
    String line = null;
    while ((line = reader.readLine()) != null) {
     if(result==null){
      result=line;
     }else{
     result += line;
     }
    }
   }
  } catch (MalformedURLException e) {
   // TODO Auto-generated catch block
   e.printStackTrace();
  } catch (IOException e) {
   // TODO Auto-generated catch block
   e.printStackTrace();
  }
  return result;
}