How to handle request / response

[Jonathan Arnold]

Oh, and another question - how does the "DefaultHttpResponse" that
handleUpstream creates get turned into the Response object that the
requestId is fetched from? If I try to the same thing, I get a Java
error saying:

java.lang.ClassCastException:
org.jboss.netty.handler.codec.http.DefaultHttpResponse cannot be cast
to com.iocom.wombat.RtspResponse



On Fri, 8 Jul 2011 12:41:59 -0700
<Michael.Newcomb at gdc4s.com> wrote:

> This is an example of what I do for request/response. I edited it in
> e-mail, so excuse any typos. 
> 
> public interface Request<R>
>   extends ChannelFutureListener
> {
>   long getId();
> 
>   void setId(long id);
> 
>   R getResponse()
>     throws InterruptedException, Exception;
> 
>   void setResponse(Object response);
> }
> 
> public interface Response
> {
>   long getRequestId();
> }
> 
> public abstract class RequestResponseChannelHandler
>   implements ChannelUpstreamHandler, ChannelDownstreamHandler
> {
>   private final AtomicLong requestCount = new AtomicLong();
> 
>   private final ConcurrentMap<Long, Request> requests = new
> ConcurrentHashMap<Long, Request>();
> 
>   public void handleUpstream(ChannelHandlerContext context,
> ChannelEvent event)
>     throws Exception
>   {
>     if (event instanceof MessageEvent)
>     {
>       MessageEvent message = (MessageEvent) event;
> 
>       if (message.getMessage() instanceof Response)
>       {
>         Request request = requests.remove(((Response)
> message.getMessage()).getRequestId());
> 
>         assert request != null;
> 
>         request.setResponse(message);
>       }
>       else
>       {
>         context.sendUpstream(event);
>       }
>     }
>     else
>     {
>       context.sendUpstream(event);
>     }
>   }
> 
>   public void handleDownstream(ChannelHandlerContext context,
> ChannelEvent event)
>     throws Exception
>   {
>     if (event instanceof MessageEvent)
>     {
>       MessageEvent message = (MessageEvent) event;
>       if (message.getMessage() instanceof Request)
>       {
>         Request request = (Request) message.getMessage();
> 
>         long id = requestCount.incrementAndGet();
>         request.setId(id);
> 
>         requests.put(id, request);
>       }
>     }
> 
>     context.sendDownstream(event);
>   }
> }
> 
> Send request:
> Request<String> r = new MyRequest();
> channel.write(r);
> String s = r.getResponse();
> 
> Handle response:
> channel.write(new MyResponse(request.getId()));
> 
> You still need handlers do encode/decode the requests and responses,
> but that is how I handle request/response.
> 
> Michael
> 
> -----Original Message-----
> From: netty-users-bounces at lists.jboss.org
> [mailto:netty-users-bounces at lists.jboss.org] On Behalf Of Jonathan
> Arnold
> Sent: Friday, July 08, 2011 9:16 AM
> To: netty-users at lists.jboss.org
> Subject: How to handle request / response
> 
> I'm a fairly inexperience Java programmer new to Netty and was
> wondering what the "standard practice" is when it comes to handling
> specific responses to specific requests.
> 
> In my case, I am doing RTSP requests to a server and I need to do
> specific things based upon the actual request. So when I do a SETUP, I
> need to get some information out of the response and then do other
> things. 
> 
> In a more general case, say I'm writing an app the uses a RESTful
> interface. I request some information that comes back in, say, XML and
> I want to process it in a special way.
> 
> How do I set up a handler for a response to a specific request? Is
> this what the "event model" mentioned in the docs is used for? If so,
> I need a little more information.
> 
> Or do I add another filter handler? Have some kind of callback? Use a
> special response handler for each request?
> 
> Some real world source code examples would be great. The http examples
> in the Netty code don't deal with this case. They are either one shots
> or don't really do anything with the responses.
> 
> TIA.
> 



-- 
Jonathan Arnold        Webstream: http://hieronymus.soup.io

Talent wins games, but team work and intelligence wins championships.
Michael Jordan