Re: [Winstone-devel] Winstone and DWR

[Rick K. <ri...@kn...>]

Keda,

Thanks for telling me about this.

I did some checking, and I've found out that the DWR framework is 
actually violating Servlet Spec section SVR8.2 which says:

SRV.8.2 Using a Request Dispatcher
To use a request dispatcher, a servlet calls either the include method 
or forward
method of the RequestDispatcher interface. The parameters to these 
methods can
be either the request and response arguments that were passed in via the 
service
method of the javax.servlet interface, or instances of subclasses of the 
request and
response wrapper classes that were introduced for version 2.3 of the 
specification. In
the latter case, the wrapper instances must wrap the request or response 
objects that
the container passed into the service method.

Notice the last sentence ... the reason Winstone fails is because DWR 
passes in a response to the request dispatcher forward() that *doesn't* 
wrap the winstone response it was supplied with. Winstone tries to 
unwrap the response until it gets back to its initial response, but 
stops at the SwallowingHttpServletResponse class because it doesn't 
extend ServletResponseWrapper. Winstone assumes that when it runs out of 
wrappers, it must be the original response (as the spec requires). DWR 
is violating the spec here by passing in a response of its own.

I'll let the DWR people know about this. Thanks for bringing it up.

Rick

keda jones wrote:
> Hello All,
>
>    I am starting to use winstone in a
> small project that I am working on and so far it has been very clean to work with.  I ran in to some trouble, though, when I started using winstone in association with DWR ajax library (http://getahead.ltd.uk/dwr/).  Specifically, I have encountered the class cast error below.  It seems that DWR manufactures a ServletResponse that is not based on a WinstoneResponse.
>
>
> WARN  uk.ltd.getahead.dwr.impl.ExecuteQuery: warn() - Method execution failed:
> java.lang.ClassCastException: uk.ltd.getahead.dwr.util.SwallowingHttpServletResponse
>         at winstone.RequestDispatcher.getUnwrappedResponse(RequestDispatcher.java:444)
>         at winstone.RequestDispatcher.forward(RequestDispatcher.java:268)
>         at uk.ltd.getahead.dwr.impl.DefaultWebContext.forwardToString(DefaultWebContext.java:124)
>         at com.XXX.webform.util.AjaxUtil.buildPrecacheMap(AjaxUtil.java:57)
>         at com.XXX.webform.util.AjaxUtil.ajaxTrToggle(AjaxUtil.java:43)
>         at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
>         at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
>         at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
>         at java.lang.reflect.Method.invoke(Unknown Source)
>         at uk.ltd.getahead.dwr.impl.ExecuteQuery.execute(ExecuteQuery.java:239)
>         at uk.ltd.getahead.dwr.impl.DefaultExecProcessor.handle(DefaultExecProcessor.java:48)
>         at uk.ltd.getahead.dwr.impl.DefaultProcessor.handle(DefaultProcessor.java:81)
>         at uk.ltd.getahead.dwr.AbstractDWRServlet.doPost(AbstractDWRServlet.java:162)
>         at javax.servlet.http.HttpServlet.service(HttpServlet.java:121)
>         at javax.servlet.http.HttpServlet.service(HttpServlet.java:45)
>         at winstone.ServletConfiguration.execute(ServletConfiguration.java:249)
>         at winstone.RequestDispatcher.forward(RequestDispatcher.java:334)
>         at winstone.RequestHandlerThread.processRequest(RequestHandlerThread.java:244)
>         at winstone.RequestHandlerThread.run(RequestHandlerThread.java:150)
>         at java.lang.Thread.run(Unknown Source)
>
>
>    I have not looked at detail in to the code yet, but if anybody could give me any ideas of how this might be fixed, I would appreciate it.
>
>
>    Thanks,
>    Nathan
>
>
>
>
>  
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