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From Andy Sykes <a.sy...@ucl.ac.uk>
Subject Re: Casting an action to an interface
Date Fri, 30 Jan 2009 13:13:36 GMT
I dug around in the ServletConfig interceptor  and modified my code to  
mimic how it handles this situation - retrieve the Action as an Object  
type, test for instanceof <Interface>, the cast to it. For some  
reason, that still does not work.

As a test case, I'm mimicking the code exactly. My action extends  
ActionSupport and implements SessionAware.
In the interceptor, I retrieve the action as an Object, test if it's  
an instanceof SessionAware, then cast. Logging statements show that  
the cast never happens. If I try to skip the test and cast directly, I  
get a CCE. However, the ServletConfigInterceptor is able to do exactly  
the same thing without getting a CCE.

Either there's some messed up going on in my dev environment, or I'm  
being really dumb, or.. god knows. I've cleared out all the old  
libraries and I'm just running with the bare essentials.

Test case:
public class ParseInterceptor extends AbstractInterceptor {

     private static final Logger log =  
Logger.getLogger(ParseInterceptor.class);

     @Override
     public String intercept(ActionInvocation invocation) throws  
Exception {
         final Object action = invocation.getAction();
         if (action instanceof SessionAware) {
             log.error("Action is an instance of SessionAware.");
         }
         return invocation.invoke();
     }
}


For reference, the relevant sections in the ServletConfigInterceptor:

public class ServletConfigInterceptor extends AbstractInterceptor  
implements StrutsStatics {

	public String intercept(ActionInvocation invocation) throws Exception {
         	final Object action = invocation.getAction();
         	final ActionContext context =  
invocation.getInvocationContext();
						...snip...
		if (action instanceof SessionAware) {
             		((SessionAware) action).setSession(context.getSession());
         	}
	}
}
On 30 Jan 2009, at 12:22, Andy Sykes wrote:

> No, I don't 'need' the cast to Action. However, if I cast what I get  
> back from ActionInvocation.getAction() straight to SessionAware or  
> similar, it still chucks a CCE.
>
> I'm using Netbeans, and I'm pretty sure there's no crazy stuff going  
> on with the classloader - all my struts jars are in my context's lib  
> directory.
>
> On 30 Jan 2009, at 11:57, Nils-Helge Garli Hegvik wrote:
>
>> Do you really need the first cast to Action? Anyway, could it be that
>> you're having conflicting struts and/or application jars several
>> places in your classloader hierarchy? That could explain certain
>> "should never happen" incidents...
>>
>> Nils-H
>>
>> On Fri, Jan 30, 2009 at 12:39 PM, Andy Sykes <a.sykes@ucl.ac.uk>  
>> wrote:
>>> Hi Wes,
>>>
>>> No, I'm not using Spring at all.
>>>
>>> The Action never passes the test of being an instanceof Parseable.  
>>> If I make
>>> the action only implement SessionAware, and test if my action is an
>>> instanceof SessionAware, the test is never passed!
>>>
>>> Colour me confused!
>>>
>>> Andy.
>>>
>>>
>>> On 30 Jan 2009, at 00:55, Wes Wannemacher wrote:
>>>
>>>> On Thursday 29 January 2009 19:49:39 Andy Sykes wrote:
>>>>>
>>>>> Hi all,
>>>>>
>>>>> I've written an interceptor with a PreResultListener that gets the
>>>>> action with ActionInvocation.getAction(), then casts it to an
>>>>> interface ("Parseable", in this case). This lets me call a  
>>>>> particular
>>>>> method on the action just prior to the result being rendered.
>>>>>
>>>>> The action implements Parseable and SessionAware.
>>>>>
>>>>> When I do the cast, I get an ClassCastException for
>>>>> com.opensymphony.xwork2.ActionSupport. If I take it down to one
>>>>> interface (SessionAware) and cast the action to it, I still get  
>>>>> a CCE.
>>>>> What's weirder is I'm pretty sure this code worked on Struts  
>>>>> 2.0.11.
>>>>>
>>>>> Here's a suitably simplified version of what I'm attempting to do:
>>>>>
>>>>> public String intercept(ActionInvocation invocation) throws  
>>>>> Exception {
>>>>>      invocation.addPreResultListener(new PreResultListener() {
>>>>>            public void beforeResult(ActionInvocation invocation,
>>>>> String resultCode) {
>>>>>              Action action = (Action)invocation.getAction();
>>>>>              if (action instanceof Parseable) {
>>>>>                  ((Parseable)action).parse();
>>>>>              }
>>>>>            }
>>>>>  });
>>>>>
>>>>> Any ideas what the hell is going on here?
>>>>>
>>>>>
>>>>
>>>> Is it possible that you are using Spring to instantiate your  
>>>> actions via
>>>> the
>>>> Spring plugin? It would seem that if the action passes the test,  
>>>> then the
>>>> cast
>>>> is legal. I ask about Spring in case the action is a proxied  
>>>> bean... It
>>>> comes
>>>> up from time to time that Spring created beans don't always seem to
>>>> inherit
>>>> every method that you would think... If Spring is in the mix, try  
>>>> having
>>>> Spring use CGLIB... I've had some luck that way, vs. dynamic JDK  
>>>> proxies.
>>>>
>>>> -Wes
>>>>
>>>> --
>>>>
>>>> Wes Wannemacher
>>>> Author - Struts 2 In Practice
>>>> Includes coverage of Struts 2.1, Spring, JPA, JQuery, Sitemesh  
>>>> and more
>>>> http://www.manning.com/wannemacher
>>>>
>>>>
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>>>
>>>
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>>>
>>
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>
>
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