HttpURLConnection捕获异常null

Question

我正在执行Android应用程序开发的第一步，我使用AndroidStudio，但是当我尝试使用POST方法发送http resquest并获取结果（结果是一个简单的字符串）时，我捕获到异常消息null。

感谢您的帮助。

我试图这样做只是看我是否获得响应代码200，但仍然为null， 尝试连接中发生异常，并且e.getMessage（）返回null

       try {
            URL uri = new URL("http://google.com");
            con = (HttpURLConnection) uri.openConnection();
            rep = Integer.toString(con.getResponseCode());
        }catch (Exception e){
            //rep = e.getMessage();
            rep = " fail to connect";
        }

完整功能

public String sendPostRequest(String url, String data) {

HttpURLConnection con=null;
String rep="";

try {
                URL uri = new URL(url);
                con = (HttpURLConnection) uri.openConnection();

                con.setDoOutput(true);
                con.setRequestMethod("POST");
                con.setRequestProperty("User-Agent", "Mozilla/5.0");
                con.setRequestProperty("Content-Type", "application/x-www- 
                form-urlencoded");
                con.setRequestProperty("Content-Length", 
                String.valueOf(postData.length));

                con.getOutputStream().write(postData);
                con.getOutputStream().flush();
                con.getOutputStream().close();

                StringBuilder content;
                Reader reader = new BufferedReader(new 
                InputStreamReader(con.getInputStream()));
                StringBuilder sb = new StringBuilder();
                for (int c; (c = reader.read()) >= 0; )
                    sb.append((char) c);
                rep = sb.toString();

            }
            catch (Exception e){
                rep = e.getMessage();

            }
            finally {

                con.disconnect();
            }

            return rep;