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From oleg shteynbuk <>
Subject Re: Architecture Guide: Chain of Responsibility, Interceptor and Composite patterns
Date Thu, 03 Jul 2003 03:19:30 GMT
If your goal is to choose from GoF then the Decorator pattern will be 
the one that you will thin of. there are some similarity to decorator, 
in a sense that it is about extending functionality. But the same 
arguments that were in original mail apply to Decorator too except for 
the argument that in Chain of Responsibility the first handler that can 
handle request stops the chain. You can probably use the Decorator to 
implement the Interceptor pattern if you replace iteration with OO 
recursion, but i like the current Axis implementation, it is an 
excellent design, and Architecture Guide is very good; this particular 
part on Chain of Responsibility was a little bit misleading to me, but 
it was not a big deal because reading further it was very clear what 
handlers are actually doing.
in the Interceptor pattern there is a Dispatcher class that in addition 
to this can control the behavior of framework and not simply forward the 

POSA 1 group pattern into three categories: design, idioms and 
architectural. According to this classification GoF is about design 
patterns and POSA 1 and 2 discusses architectural patterns too. However 
when implementing the Interceptor pattern from POSA 2 GoF patterns will 
be used and i believe that Axis uses the Composite, the Iterator and 
probably the Strategy and some others.

 oleg wrote:

>In GoF, the closest pattern should be "decorator", not chain of
>                      oleg shteynbuk                                                 
>                      <oshteynbuk@nyc.         To:    
>            >                  cc:                                
>                                               Subject: Architecture Guide: Chain of Responsibility,
Interceptor and Composite      
>                      27/06/2003 07:00         patterns                              
>                      PM                                                             
>                      Please respond                                                 
>                      to axis-dev                                                    
>Thanks for "Axis Architecture Guide" it was very useful to me.
>Below is a feedback::
>1)    In "Message Flow Subsystem" -> "Handlers and Chains" under the
>second diagram first paragraph:
> "A Chain also has similarities to the Chain of Responsibility design
>pattern in which a request flows along a  sequence of Handlers until it
>is processed. Although an Axis Chain may process a request in stages
>over   a succession of Handlers, it has the same advantages as Chain of
>Responsibility: flexibility and the ease with which new function can be
>I don't believe that there are similarities to the Chain of
>Responsibility design pattern. GoF implies that each handler in the
>chain either handlers the request completely and chain stops there, or
>if it could not handle the request then it passes the request to its
>successor without doing anything. "The Design Patterns Smalltalk
>Companion" book in chapter on Chain of Responsibility discusses OO
>recursion and says that examples of Chain of Responsibility is hard to
>find and considers Chain of Responsibility a specialization of
>Object-Oriented recursion but we do not have recursion here, it looks
>more like an iteration.
>Flexibility and the ease with which new function can be added are also
>different. In the Chain of Responsibility handlers are chained and each
>handler has a reference to the next one and it is usually used if you
>want to configure chain at run time. In Axis handlers usually are
>configured at design time in deployment configuration and we have more
>like AOP interceptors and some processing or weaving is needed before we
>can use it.
>Interceptors and AOP becoming increasingly popular, and a lot of
>developers are familiar with it, did i mention JBoss. Interceptor would
>be also more descriptive word then handler.
>BTW recently has a discussion "Opinion: Interceptors
>should be added to J2EE".
>it make sense to replace the Chain of Responsibility paragraph with:
>"Handlers act like interceptors, the Interceptor pattern is in POSA 2
>2)    The sentence before the same diagram in "Message Flow Subsystem"
>-> "Handlers and Chains"
>"A Chain is a composite Handler, i.e. it aggregates a collection of
>Handlers as well as implementing the Handler interface as shown in the
>following UML diagram:"
>and after the diagram it make sense to add the following sentence to
>clarify relationship to the GoF Composite pattern.
>"Interface Chain acts like a Composite and interface Handler like a
>Component  from the GoF Composite pattern. In GoF Component is a common
>abstract class; in Axis Handler is an interface that Chains and Handlers
>implement so they could be treated uniformly."
>I believe that Composite pattern usage is related to item 4 in the "Open
>Issues" chapter.
>3)     The Iterator pattern could be mention too and there are other
>patterns that are used internally in Axis. Maybe it make sense to have
>two Architectural Guides, one simplified version for Axis users and
>another one with all patterns for Axis developers.

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