Paul Speed wrote:
> [EMAIL PROTECTED] wrote:
> >
> > Can you argue about how Valve's single chain of command ( where
> > authentication, generation, etc are done in a single invoke() ) can
> > be better than what all other server are doing ( and Apache 2.0
> > moves to a different level with the flexible HOOK mechanism ?
> >
>
> Actually, this is a discussion I would like to see happen. I
> think that I can actually argue for Valves. Admittedly, I know little
> about the actual implementations but I am very familiar with the
> patterns used in Tomcat 3.x and Tomcat 4.x and I have seen much of the
> discussions on this list. However, in other projects I have converted
> several architectures using patterns similar to 3.x to be more like the
> Valve approach. We did it to shorten development times and improve
> developer productivity. Performance wasn't our main goal but in all
> but one case performance improved.
>
Valves implement the "Chain of Responsibility" design pattern in the GoF book.
You will also see a very similar programming model in the way that the
javax.servlet.Filter APIs are defined in the Servlet Specification, Version 2.3
Proposed Final Draft -- after wrestling with lots of alternatives, the expert
group concluded that this was the most appropriate programming model for
exposing similar functionality at the application level.
>
> What I would like to see is a frank analysis of this topic.
> If those "in the know" do not have the time then I will attempt to
> do a brief analysis myself in the coming weeks. It will take research
> on my part whereas some of you might know the answers off the top of
> your head.
>
I did an analysis on this topic in August, when Catalina was being formally
proposed -- it is still in the "jakarta-tomcat-4.1" CVS repository as file
"catalina/docs/filters.html". The comparison was primarily to the way that
request interceptors were implemented in Tomcat 3.2, so I would suspect that
there have been some changes since on the HEAD branch -- particularly in the
last section, where I discuss limitations that are due to the *implementation*
of request interceptors in Tomcat 3.2, not their *design*. (The Valve APIs have
not needed to be changed -- they have proven to be entirely sufficient to
implement the servlet 2.3 spec's functionality requirements :-).
Aside from downloading the 4.1 source repository, this document will also be
visible though the online CVS web access. Sorry, I'm offline at the moment, so
I cannot give you a hyperlink, but select the CVSWeb link, module
"jakarta-tomcat-4.1", directory "catalina", directory "docs", directory "dev",
and file "filters.html".
>
> What I intend to compare is the typical method call sequence
> of the two approaches, including resource allocation if any, when
> handling various types requests. From there I hope to point to the
> relative merits and tradeoffs of each approach.
>
> I have fun with this kind of stuff... it harkens back to
> my old graphics programming days. It's almost always surprising
> what this stuff will turn up.
>
> -Paul Speed
>
I had a Comp Sci prof that made an interesting point -- you only write one real
program in your life, and then you spend the rest of your career plagarizing
from it :-)
Craig
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