Servlet 3.0: Can't send an asynchronous response?

I'm having trouble establishing AsyncContexts for users and using them to push notifications to them. On page load I have some jQuery code to send the request:

$.post("TestServlet",{
    action: "registerAsynchronousContext"
        },function(data, textStatus, jqXHR){
            alert("Server received async request"); //Placed here for debugging   
  }, "json");

And in "TestServlet" I have this code in the doPost method:

HttpSession userSession = request.getSession();
String userIDString = userSession.getAttribute("id").toString();

String paramAction = request.getParameter("action");

if(paramAction.equals("registerAsynchronousContext"))
{              
    AsyncContext userAsyncContext = request.startAsync();

    HashMap<String, AsyncContext> userAsynchronousContextHashMap = (HashMap<String, AsyncContext>)getServletContext().getAttribute("userAsynchronousContextHashMap");
    userAsynchronousContextHashMap.put(userIDString, userAsyncContext);
    getServletContext().setAttribute("userAsynchronousContextHashMap", userAsynchronousContextHashMap);

    System.out.println("Put asynchronous request in global map");
}

    //userAsynchronousContextHashMap is created by a ContextListener on the start of the web-app

However, according to Opera Dragonfly (a debugging tool like Firebug), it appears that the server sends an HTTP 500 response about 30000ms after the request is sent.

Any responses created with userAsyncContext.getResponse().getWriter().print(SOME_JSON) and sent before the HTTP 500 response is not received by the browser, and I don't know why. Using the regular response object to send a response (response.print(SOME_JSON)) is received by the browser ONLY if all the code in the "if" statement dealing with AsyncContext is not present.

Can someone help me out? I have a feeling this is due to my misunderstanding of how the asynchronous API works. I thought that I would be able to store these AsyncContexts in a global map, then retrieve them and use their response objects to push things to the clients. However, it doesn't seem as if the AsyncContexts can write back to the clients.

Any help would be appreaciated.

I solved the issue. It seems as though there were several problems wrong with my approach:

1. In Glassfish, AsyncContext objects all have a default timeout period of 30,000 milliseconds (.5 minutes). Once this period expires, the entire response is committed back to the client, meaning you won't be able to use it again.

   If you're implementing long-polling this might not be much of an issue (since you'll end up sending another request after the response anyway), but if you wish to implement streaming (sending data to back to the client without committing the response) you'll want to either increase the timeout, or get rid of it all together. This can be accomplished with an AsyncContext's .setTimeout() method. Do note that while the spec states: "A timeout value of zero or less indicates no timeout.", Glassfish (at this time) seems to interpret 0 as being "immediate response required", and any negative number as "no timeout".

2. If you're implementing streaming , you must use the printwriter's .flush() method to push the data to the client after you're done using its .print() .println() or .write() methods to write the data.

3. On the client side, if you've streamed the data, it will trigger a readyState of 3 ("interactive", which means that the browser is in the process of receiving a response). If you are using jQuery, there is no easy way to handle readyStates of 3, so you're going to have to revert to regular Javascript in order to both send the request and handle the response if you're implementing streaming.

I have noticed that in Glassfish if you use AsyncContext and use .setTimeOut() to a negative number the connection is broken anyway, to fix this I had to go to my Glassfish admin web configurator : asadmin set configs.config.server-config.network-config.protocols.protocol.http-listener-1.http. And set timeout to -1. All this to avoid glassfish finish the connections after 30 sec.