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From "Paulo Gaspar" <>
Subject RE: Interceptors ( was Re: 3.x vs 4.0 architecture Q's
Date Thu, 18 Jan 2001 23:29:55 GMT
> -----Original Message-----
> From: Craig R. McClanahan []
> Sent: Thursday, January 18, 2001 23:04
> One appropriate question to ask yourself, when comparing, is 
> "what does having 15
> entry points give me that I cannot get with a single entry point 
> approach"?  If
> there is nothing significant, then it would seem cleaner to rely on a
> simpler-to-understand approach.

That is a problem also found in several parts of business application 
frameworks - those things that help you building a big User Interface 
to manipulate and extract information from a big Database.

You also find the same questions over GUI Frameworks - like Delphi's 
VCL or Java's Swing. And in database interface libraries...

In all of these you find events (Hooks) named "onThis", "beforeThat"
and "afterSomethingElse". And all this frameworks are built using 
Object Oriented Programming Techniques.

The advantage of Hooks is that the programmer is only exposed to the 
very narrow complexity of a very specific event. The framework takes
care of the rest.

When you build your own thing that you put in a logic/data pipe, 
sometimes you have to understand a lot more about the inner working
of the framework in order not to screw anything.

So, it is not as straightforward as you put it. It is a case by case 

> Also, IMHO, copying a web server (written in C, by the way) 
> architecture, in and
> of itself, is not a compelling argument to influence the design 
> of a servlet
> container written in an object oriented language like Java.  The 
> question is
> really "what's in it for Tomcat?".

Apache is not a complete model for building Tomcat, but provides some 
interesting ideas one can learn from. The small core general idea is
a classic in flexible systems, but the focus here is on the hooks.

Apache gives a tested answer to the question of which hooks are enough.

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