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From Daniel Fagerstrom <dani...@nada.kth.se>
Subject Re: Pipeline components and Object Model issues
Date Sun, 19 Aug 2007 20:30:35 GMT
Grzegorz Kossakowski skrev:
[Snipping lots of technical details]
> I want to create dynamic proxies around pipeline components. Actual 
> wrapping would be performed by class implementing BeanPostProcessor 
> interface. Taking one perspective one could say that this it's almost 
> the way as discussed one paragraph above. However, going with this path 
> makes whole pipeline scope completely *orthogonal* to the pipeline and 
> its components' code. No existing class will be touched and there is no 
> requirement on pipeline components' configuration files. No need for 
> custom namespace in XML config, etc.
> 
> I feel proud of this solution as it solves non-trivial problem just in 
> few lines of code and few config files in transparent way. 8-)

Seem like a neat solution.

Actually there are more that could be done with BeanPostProcessors.

As you know sitemap components has a rather involved life cycle, where 
they first are created by the container and then the setup method is 
called in the pipeline to insert the object model, the parameters and 
some other stuff. Now if these objects already are part of the sitemap 
scope, we could have a special SitemapModelComponent aware 
BeanPostProcessor that just takes the needed objects from the current 
scope and use the for setting up the sitemap component.

What is needed is that the right scope is set before looking up the 
sitemap component from the container. This will only work for prototype 
scoped beans as we must be sure that they actually are created in the 
scope where they are looked up. All Springified sitemap components are 
prototypes, (I don't know how it would work for the Avalon bridge 
handled components).

This far we only have a possible simplification of the setup mechanism. 
But with other BeanPostProcessors we could get the same style of 
interceptor based dependecy injection as in Struts2, where various 
request objects are injected in the action bean based on marker 
interfaces. We could do something similar for sitemap components and 
maybe go further and have convention based autoviring so e.g. a set 
method that takes a ServletRequest automatically get the one from the 
call injetcted.

We could use the same mechanism for a new type of actions that are 
created in prototype scope and get all dependencies injected by Spring 
in the sitemap scope.

/Daniel

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