> Yeah, I've used variations on this pattern to help save architectures
> that were spiralling out of control.
You may also check:
http://jakarta.apache.org/cvsweb/index.cgi/~checkout~/jakarta-tomcat/src/doc/internal.html
( it's not up-to-date, a everything is now much cleaner, and most of the
optimizations have been made )
Another interesting source of information is Apache 1.3 and Apache 2.0,
and the HOOKS mechanism introduced in 2.0.
Tomcat 3.3 is following the same model and direction ( by providing more
hooks and a more flexible mechanism to deal with the chains ).
It should also be noted that 3.3 supports _both_ Valves ( i.e. a chain
on the invoke() hook ) and Apache style hooks ( auth, config, error
handling, mpm, etc ). Of course, most 3.3 modules are using the more
flexible aproach and the specialized chains instead.
You may also note that most web servers ( IIS, NES ) are using the same (
multiple chains ) pattern as Tomcat 3.3.
( the "valve" chain has allways been possible in tomcat3.x, by extending
Handler/ServletWrapper using the same pattern, but never used because of
the belief that Apache2.0 model is better. The reason for exposing it more
in 3.3 is to allow porting of valves - as independent and standalone
modules - from 4.0, i.e. to reuse existing code instead of reinventing it
for some usefull modules )
BTW, the AccessLogValve has already been adapted ( as a 3.3 module), and
will be made available soon ( after I find a place to distribute the
modules out of ). ( I find to be very usefull, and it was the first test
that the 3.3 model works and is flexible enough ).
--
Costin
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