Pipelines

[Daniel Rall <dl...@finemaltcoding.com>]

Ilkka, I'm curious about your thoughts on the Tomcat/Turbine pipeline
versus Servlet API FilterChains.  My knowledge of Filters and
FilterChains indicates that they give only one direction of filtering,
whereas with the pipeline, you get another whack at filtering as
Valves pop off the stack.  What is your evaluation of the flexibility
provided by the 3.0 pipeline versus the simplicity of the Servlet API?
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Daniel Rall <dl...@finemaltcoding.com>

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Re: Pipelines

[Ilkka Priha <ip...@surfeu.fi>]

Dan, I don't  think there is any significant difference between the two 
from technical point of view. Nevertheless, Pipelines are Tomcat's 
implementation mechanism for Servlet API's FilterChains. We've 
implemented the original Turbine 3 Pipelines as FilterChains because of 
standardization. If we hadn't applied Servlet API, we'd have to choose 
between Tomcat Pipelines, Turbine Pipelines and new Pipelines of our 
own. In such situation, I always prefer common solution over minor 
technical advantages.

In practice, our implementation is much closer to Turbine 3 Pipelines 
than simple Servlet API Filters. This is possible by applying the same 
wrapping  technology for FilterChain that is available for 
ServletRequest and ServletResponse (and which we also apply instead of a 
separate RunData object). That is, we wrap the incoming FilterChain 
implementation within the first Filter with our own implementation 
providing the additional features, such as grouping sets Filters to 
Pipes and branching between Pipes. Client objects, which need these 
features, have to do type casting, but most clients see the simpler and 
standardized FilterChain. By this way, we obtain the best from both 
solutions :-)

The main benefit is that we don't have to explain, justify and document 
for users yet another compilicated servlet request mechanism, but can 
simply refer to a standard API and all material already published around 
it. Advanced features are only extensions to the standard. In addition, 
Tammi can now be executed either as a standalone, as a servlet or as a 
filter chain. And Filters (Valves) can be configured with xml without 
specifying and programming an application specific schema and its parser ;-)

-- Ilkka


Daniel Rall wrote:

>Ilkka, I'm curious about your thoughts on the Tomcat/Turbine pipeline
>versus Servlet API FilterChains.  My knowledge of Filters and
>FilterChains indicates that they give only one direction of filtering,
>whereas with the pipeline, you get another whack at filtering as
>Valves pop off the stack.  What is your evaluation of the flexibility
>provided by the 3.0 pipeline versus the simplicity of the Servlet API?
>  
>





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