为什么没有inputStream的outputStream无法工作？

Question

我试图在localHost上连接PHP脚本，但是如果没有inputStream，就无法访​​问该脚本。偶然地我使代码正常工作，但不知道为什么在存在inputStream而不是在没有InputStream的情况下

 try {
        String url= "10.0.2.2/arrival.php";
        URL loginurl= new URL(url);
        HttpURLConnection http= (HttpURLConnection)loginurl.openConnection();
        http.setRequestMethod("POST");
        http.setDoOutput(true);
        http.setDoInput(true);

        OutputStream out= http.getOutputStream();
        BufferedWriter bfwr= new BufferedWriter(new OutputStreamWriter(out,"UTF-8"));
        String post_data= URLEncoder.encode("renter_id","UTF-8")+"="+URLEncoder.encode(renter_id,"UTF-8");

        bfwr.write(post_data);
        bfwr.flush();
        out.close();
        bfwr.close();

        InputStream inpt= http.getInputStream();
        BufferedReader bfrdr= new BufferedReader(new InputStreamReader(inpt,"iso-8859-1"));
        String line="";
        String result="";
        while((line=bfrdr.readLine())!=null){
            result+=line;
        }
        bfrdr.close();
        inpt.close();
        http.disconnect();

        return "";

} catch (MalformedURLException e) {
    e.printStackTrace();
} catch (ProtocolException e) {
    e.printStackTrace();
} catch (IOException e) {
    e.printStackTrace();
}