The suspend/resume style is used when a servlet and/or filter is used to generate the response after an asynchronous wait that is terminated by an asynchronous handler. Typically a request attribute is used to pass results and to indicate if the request has already been suspended.

void doGet(HttpServletRequest request, HttpServletResponse response)
{
     // if we need to get asynchronous results
     Object results = request.getAttribute("results");
     if (results==null)
     {
       final Continuation continuation = ContinuationSupport.getContinuation(request);

       // if this is not a timeout
       if (continuation.isExpired())
       {
         sendMyTimeoutResponse(response);
         return;
       }

       // suspend the request
       continuation.suspend(); // always suspend before registration

       // register with async service.  The code here will depend on the
       // the service used (see Jetty HttpClient for example)
       myAsyncHandler.register(new MyHandler()
       {
          public void onMyEvent(Object result)
          {
            continuation.setAttribute("results",results);
            continuation.resume();
          }
       });
       return; // or continuation.undispatch();
     }

     // Send the results
     sendMyResultResponse(response,results);
}

This style is very good when the response needs the facilities of the servlet container (e.g., it uses a web framework) or if one event may resume many requests so the container’s thread pool can be used to handle each of them.

The suspend/complete style is used when an asynchronous handler is used to generate the response:

void doGet(HttpServletRequest request, HttpServletResponse response)
{
     final Continuation continuation = ContinuationSupport.getContinuation(request);

     // if this is not a timeout
     if (continuation.isExpired())
     {
       sendMyTimeoutResponse(request,response);
       return;
     }

     // suspend the request
     continuation.suspend(); // response may be wrapped.

     // register with async service.  The code here will depend on the
     // the service used (see Jetty HttpClient for example)
     myAsyncHandler.register(new MyHandler()
     {
       public void onMyEvent(Object result)
       {
         sendMyResultResponse(continuation.getServletResponse(),results);
         continuation.complete();
       }
     });
}

This style is very good when the response does not need the facilities of the servlet container (e.g., it does not use a web framework) and if an event will resume only one continuation. If many responses are to be sent (e.g., a chat room), then writing one response may block and cause a DOS on the other responses.