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From "Will Hartung" <wi...@msoft.com>
Subject Re: more about custam tag life cycle
Date Mon, 03 Feb 2003 19:00:46 GMT
> From: "Felipe Schnack" <felipes@ritterdosreis.br>
> Sent: Monday, February 03, 2003 10:12 AM
> Subject: RE: more about custam tag life cycle


> This makes me feel muuuuuch better :-)

On Mon, 2003-02-03 at 16:09, Tim Moore wrote:
> This is NOT true, AFAIK.  The same tag instance can be used multiple times
*sequentially*
> but not *concurrently*.  Check out the lifecycle state diagram in the JSP
spec.

The way to look at it is simply that the generated code is going to use a
tag pool for each distinct class of tags. Unfortunately, there is no
specific action that tells the tag it is being pulled from or being put back
from the pool.

All tags follow the basic lifecycle of simpy
constuctor
setPageContext
doStartTag
doEndTag

In the pooled environment, it's:
constructor
setPageContext
doStartTag
doEndTag
doStartTag
doEndTag
etc.

(I've seen some containers, I thinik Tomcat is one, that call setPageContext
on each tag, but I've seen others that do not, so setPageContext is not a
reliable method to reset the tag properties).

If the tag implments the TryCatchFinally interface, then a doFinally is
called after the doEndTag.

What's is non-obvious is that the doEndTag and doFinally are supposed to
assume the role of cleaning the tag up for reuse.

I particularly like this quote from the spec:

"The particular code shown below assumes there is some pool of tag handlers
that are managed (details not described, although pool managing is simpler
when
there are no optional attributes),"

This entire problem, at least as I've encountered it, revolves around not
only optional, but also contradictory tags (i.e. it's okay to specify
paramter a, b, or c, but no combination in the same tag).

And like I said earlier, it would be nice if there were a pool interface
added to the lifecycle to clean up the tag processing to make optional
properties more portable and easier to write for.

Regards,

Will Hartung
(willh@msoft.com)




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