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From "Jing Zhou" <j...@netspread.com>
Subject Struts-chain Behavior Discussion
Date Fri, 03 Oct 2003 20:53:35 GMT
It looks to me that I threw a disturbing idea. Now I change
the subject for more discussions of different opinions.

Craig mentioned the "go to" statement in programming
languages and hinted it could be an evil if Chain implement
the semantics of "go to" (I just called it "jump behavior").

If we recognize Chain as a high level pattern regulator,
I would not agree such a comparison is appropriate
unless someone could convince me the following
observations are questionable.

* I studied several workflow engines (not page flow stuff, they
  manage persisted workload for people) They all implement,
  one way or another, the "jump behavior". I could not see
  they violate the OO design principles as high level
  regulators.

* Struts itself, as a MVC pattern regulator in its core, 
  implements the "go to" semantics when Action returns a
  ForwardConfig. It does a "go to" the next page, right? -:)

In another word, IMHO, low level language principles
may not be applicable to high level pattern/structure
regulators. Hope people re-think it.

I also recognize the facts that we do not want to overgrow
Chain into an xml based rule engine. It should be just chain.
But for such a simple requirement, one way is to model it
as a "if" decision (Craig way), another way is to model it
as a pseudo controller (Ted way). They are kind of 
cumbersome to use. It violates the "Simple thing should
be simple" principle - a principle that supercedes other
programming principles. The Filter thing could offer a
simple solution, but I haven't looked it in details yet.

The "jump behavior" requirement is very obvious in 
Java Server Faces Specification too. When the 
renderResponse() is called on FacesContext, the control
is transferred to the Render Response phase after
the current phase. This is another evidence of the
"jump behavior" in high level pattern regulators.

I would like people to open mind and think, if we
add a method in Chain that allows us to execute
the chain starting with a given index (currently
the starting index is 0). Will that make the thing simple?
Or the idea is still disturbing somewhere?

Jing

Netspread Carrier
http://www.netspread.com


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