Re: [Webmacro-devel] Re: [Melati-developers] WebMacro Test Case: TestSharedOutputStream

[Keats <ke...@xa...>]

I think Lane's solution is ultimately best -- don't try to write to the
underlying stream from within a template, just return a String and let WM
handle it.

If you do need/want to do this for some reason, you can still get ahold of
the FastWriter by putting it into the context.  If you don't want to use the
deprecated getFastWriter, you can manage the FastWriter explicitly:

// create a context for the current request
WebContext c = _wm.getWebContext(req,resp);
// put junk in the context
//...
// create a FastWriter
FastWriter fw = FastWriter.getInstance(c.getBroker(),
c.getResponse().getOutputStream());
// put the FastWriter into the context
c.put("fw", fw);
// get the template
WMTemplate t = (WMTemplate)_wm.getTemplate("mytemplate.wm");
// write the template to the output, using our context
t.write(fw, c);
fw.close();

Hope this helps.

Keats

----- Original Message ----- 
From: Lane Sharman
To: Tim Joyce
Cc: mel...@li... ;
web...@li... ; Tim Pizey
Sent: Sunday, March 14, 2004 12:02 PM
Subject: Re: [Webmacro-devel] Re: [Melati-developers] WebMacro Test Case:
TestSharedOutputStream


Hi Tim,

Thanks for adding your .2p. I'd like to get to the best solution now that we
are in the thick of this.

While I agree, as you suggest, that you _could_ flush to the output stream.
I would not propose that we try to follow this path. It breaks a lot of
encapsulation issues at play and getting a handle onto the instance that
controls the backing store, the cached FastWriter instance, will be tricky.
I see no way to reach out and get this other than thru some AOP technique.

What I do propose is that the type, MarkupLanguage, return its output
instead of writing its output. This follows the well-known pattern of
context objects. I think there are a lot of good arguments for refactoring
this type to behave in this manner. If there are some downsides to this, I'm
sure you will let me know.

thanks,

Lane


Tim Joyce wrote:

Lane,

I have only spent 5 mins on this, so much of this is from memory, but here
is my 2p.


The problem, as presented by Keats, is that in 2.0, WM renders a
template to a backing store using a FastWriter impl instance, not to the
outputstream. I kinda knew this to be the case but could not verify it.


it always did this (buffered the output stream).


Therefore, prior to 2.0, Melati exploited its knowledge of the behavior
of FW. With 2.0, this knowledge of the WM implementation is no longer
correct. WM writes to a backing store in 2.0, not directly to the output
stream.


ok.


The FastWriter instance used internally to write out a template is not
visible to the template in 2.0. In 2.0, you write to an output stream or
to a string. In 2.0, as has been noted, the reference to the FW instance
used to render the template internally is not available.



Personally, I think it is bad form that melati exploited internal
knowledge of the FW mechanics. This broke the encapsulation contract and
now melati is broken. The melati template variable, $ml, instead of
returning strings for method calls, has an internal operation which
writes to the output stream. Since the template is buffered, this write
op ends up at the front of the output.


i would not cast blame here.  the outputstream was (and still is) exposed
therefor it is not unreasonable to reference it elsewhere.  without an
explicit unit test the contract is ambiguous, and melati made the assumption
that it was allowed to make direct write calls to the outputstream.
similarly, changing the implementation of FastWriter is also totally
reasonable.


My suggestion at this point is to back out the exploited knowledge. $ml,
a context variable and object, should return renderable text, not
attempt to write to the output stream. This would decouple it from
internal knowledge of the templating frameworks and standardize its
behavior in a normal manner for all template engines, not just WM.


why can't we just flush() before we write our stuff.

timj






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