HttpURLConnection returns overlaping responses for concurrent requests

Question

Hi,
we are facing an issue in making HttpURLConnection requests. Our servlet has to make HttpURLConnection to another server (Both request and response body to be passed is xml, that is the contract with server which we are firing requests to). User can fire 2 concurrent requests one after another with out waiting for first request to be completed. When two requests are fired, two threads are executing the below block of code with no time. And the problem is first response is empty second response contains data for both responses
           URL url = new URL(urlStr);
            HttpURLConnection c = (HttpURLConnection) (url.openConnection());
            c.setRequestMethod("POST");
            c.setRequestProperty("Content-Type", "text/xml; charset=\"utf-8\"");
            c.setDoOutput(true);
            out = new BufferedOutputStream(c.getOutputStream());
            out.write(requestData.getBytes("UTF-8"));
            out.close();
            String inputLine = null;
            StringBuffer sBuffer = new StringBuffer();          
            in2 = new BufferedReader(new InputStreamReader(c.getInputStream(), "UTF-8"));
            while ((inputLine = in2.readLine()) != null) {
                sBuffer.append(inputLine);
                sBuffer.append("\n");
            String responseXML = sBuffer.toString();and the above code is in separate static class. we tried using third party implementations for HttpURLConnection instead of sun implementation. NO LUCK.
Any help in resolving this issue would be of great help
Thanks,
JKChaitanya

Answer 1

JKChaitanya wrote:
"in2" is also local variable to the method, only "requestData" comes from servlet's doPost method, all other variables are local to the method in which HttpURLConnection code is availableIt seems to me that the implication is that the server you are chaining to is not thread safe and can only handle one request at a time. This means that you will have to process the requests sequentially. Two obvious approaches - use synchronisation or use a request queue. To test the hypothesis it would be very easy to use synchronisation on your servlet class object. Note - you cannot reliably synchronise on the servlet instance since your server may be configured to use more than one instance.