[seam-dev] Re: [Richfaces-exadel] Concurrent requests (event queue and error condition)

Pete Muir pmuir at redhat.com
Tue Sep 2 17:22:24 EDT 2008

On 2 Sep 2008, at 19:49, Pete Muir wrote:

> On 2 Sep 2008, at 19:19, Ted Goddard wrote:
>> Hi Pete,
>> The ICEfaces bridge can handle errors to various Ajax responses;  
>> for instance,
>> in some cases the icon in the connection status component will be  
>> changed to
>> reflect an error response.
> Ok, this is good - means that it should work as it is today with  
> IceFaces.
> Seam requires a bit of a rejig to make it do this, so I'll work on  
> that next.

So, Seam now throws an exception when it can't serialize a concurrent  
request, and you can use Seam's standard exception handler to  
translate that into the appropriate response (e.g. redirect to an  
error page, send an http error code).

I've tested A4Js error handling, and it all works well (e.g. you can  
pop up a message to the user).

Shane, can Seam remoting deal with an HTTP error being sent to it?

The changes the user will need to make:

1) Define the exception handling in pages.xml to either send an HTTP  
error or go to an error page. Sending a 503 error with logging turned  
off will be the recommended approach.
2a) A4J: alter their templates to override the A4J error handling
2b) ICEfaces: ??? (do nothing by the sound of it)
2c) Seam Remoting: ???

Currently the system boots them out of the conversation, we replace  
that with throwing an exception, both are equally bad so this  
shouldn't be too much of regression for existing apps.

>> So responding with an error to the Ajax request sounds good ... the  
>> question is
>> how it should be displayed to the user.  Or should this error cause  
>> a retry
>> over Ajax after some period of time (and not be displayed to the user
>> immediately)?
> I think both these are reasonable options, and should be up to the  
> developer to choose one. I would say the default behaviour should be  
> to display a message to the user.

It would be great if we could get an example of how to do these for  
ICEfaces, A4J and Seam remoting into the ref doc. Sergey/Ted/Shane can  
you provide me with an example of how to customize the behaviour of  
the framework in both these ways when an HTTP 503 error is sent as the  
AJAX response?


>> Regards,
>> Ted.
>> On 2-Sep-08, at 12:06 PM, Pete Muir wrote:
>>> Ted, Judy, Shane,
>>> I've recently been working on https://jira.jboss.org/jira/browse/JBSEAM-1832 
>>>  and am trying to define better what Seam should do when it cannot  
>>> successfully serialize requests to the conversation scope (because  
>>> the queue times out). My preferred solution is to drop the  
>>> request, and send an error to the browser for it to deal with. I'm  
>>> looking for your input on the best way to send such an error that  
>>> will work with different remoting/ajax frameworks.
>>> A couple of points
>>> 1) Should work ootb - the user should just get some error message  
>>> in the browser by default, which they can customize
>>> 2) Should work the same for all different JS frameworks
>>> Having looked at A4J, I notice that it can handle being sent an  
>>> HTTP error. Semantically, it seems correct to approach it this way  
>>> (specifically sending a 503) but if we do that, we need a way for  
>>> (at least) Seam Remoting, A4J and IceFaces to intercept that  
>>> request and translate it to a message to the user (and not bring  
>>> up an ugly error message).  We can send a detailed error message  
>>> as the body of the message (e.g. concurrent request) and perhaps  
>>> add a http header that shows where this error comes from.
>>> WDYT?
>>> On 2 Sep 2008, at 18:55, Pete Muir wrote:
>>>> Seam serializes, also using a timed queue. We need to do  
>>>> *something* when the event reaches the timeout. Currently, Seam  
>>>> will make the active conversation inactive, which isn't the best  
>>>> behaviour, and I think the correct approach is to stay in the  
>>>> conversation, but to send an error. I took a look at the A4J  
>>>> error handling, and it looks like the best approach is to send an  
>>>> Http error to the browser, which can then be intercepted and  
>>>> handled? Can we provide a default behaviour for this?
>>>> Thanks,
>>>> Pete
>>>> _______________________________________________
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>>>> Richfaces-exadel at redhat.com
>>>> https://www.redhat.com/mailman/listinfo/richfaces-exadel
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