URLFetch Service always sending null on POST request

Question

I am having a bit of trouble with URLFetch service that it is always sending a json String as null:

            url = new URL(URL);
            HttpURLConnection conn = (HttpURLConnection) url.openConnection();
            conn.setDoOutput(true);
            conn.setRequestMethod("POST");
            conn.setConnectTimeout(GAE_PUMP_TIME);
            writer = new OutputStreamWriter(conn.getOutputStream());
            writer.write(jsonString);
            writer.close();

            if(conn.getResponseCode() == HttpURLConnection.HTTP_OK || conn.getResponseCode() == HttpURLConnection.HTTP_NO_CONTENT){
                LOG.info("Response: " + "OK");
                setStatus(Status.SUCCESS_OK);
            } else {
                LOG.info("Response: " + "ERROR");
                setStatus(Status.SERVER_ERROR_INTERNAL);
            }

The above code is always throwing server error due to the fact that when we inspected the data sent or received by the server is null.

I tried send through other REST client (like Curl) the String jsonString manually, and the server is able to process. So this concludes that the data is well-formed. The question is why GAE URLFetch service when doing POST method it cannot send the jsonString what is missing in my code?

Answer 1

I'm not having this problem from Python (none of my Java apps post JSON). The only thing of significance I see is that when POSTing JSON, my apps set the Content-Type header to application/json .