I'm not sure what the requirements are wrt properties and specific users.
I've done similar things on a "per request" basis via doing something like:
public abstract int getProp();
public abstract void setProp(int value);
public int getComplicatedValue()
{
if(getProp() == -1) {
// do something complicated
setProp(newVal);
}
return getProp();
}
The idea being that the heavy operation will only happen once for that
request/response cycle.
This all changes if you want it to be done for "all users" ? You can do that
as well I suppose but I think I probably need more clarification on who the
properties are supposed to be exposed to/etc..
On 10/10/06, Epstein, Ezra <[EMAIL PROTECTED]> wrote:
That's the opposite of the functionality I want. These are not PER
request. They are per instance of a component. Thus true instance
variables are the way to go. Tapestry recycles Components and it seems that
within a request the same component is re-used but not cleared (ivars reset)
even though it is re-parametrized. So, I don't think request vars would
work.
Thanks,
Ezra Epstein
Amazon.com - Developer Tools
206-266-2259
-----Original Message-----
From: andyhot [mailto:[EMAIL PROTECTED]
Sent: Tuesday, October 10, 2006 12:35 AM
To: Tapestry users
Subject: Re: How to observe property binding events
Why store them in local variables?
Store it in the current request cycle...
First do a cycle.getAttribute("myexpensivevar") if that returns null, do
the computations and store the result back cycle.setAttribute
("myexpensivevar",obj);
See
http://tapestry.apache.org/tapestry4/tapestry/apidocs/org/apache/tapestry/IRequestCycle.html
Epstein, Ezra wrote:
> OK, let's get to brass tacks.
>
> I have some derived values that are somewhat expensive to compute so I
compute them once per request/response cycle and then they're in local
instance variables (non-persisted).
>
> The particular component in question (with the semi-expensive derived
values) is used inside a loop and so may appear multiple times on a
page. By default the first time I use the component I compute the value and
then display from that computed value... The 2nd, 3rd, etc instance of
those component on the page is actually the exact same Java instance and so
the computed/derived ivar is still set. I've added a hack that records an
original property value when the derived ivar is computed and if the
original and current property values don't match I reset the derived
ivar. It works, but it a total hack.
>
> The common way I'd imagine doing it is to listen to when the property
(parameter) is set by Tapestry. But now that I've lain out the use case
maybe some knows the "right" way to do this in Tapestry.
>
>
> Thanks,
>
> Ezra Epstein
>
>
> -----Original Message-----
> From: Jesse Kuhnert [mailto:[EMAIL PROTECTED]
> Sent: Monday, October 09, 2006 3:33 PM
> To: Tapestry users
> Subject: Re: How to observe property binding events
>
> There's also the org.apache.tapestry.event.ChangeObserver interface,
> though this is currently only used by the services in tapestry.persist
> to observe page property changes when they are being managed via a
> particular persistence strategy. (like session/client/etc..)
>
> ~Maybe~ it's an oversight, and maybe not..I guess that depends on
what/why you are trying to do. You'll find that there is very little in the
framework that wasn't put there for an actual need, so adding in support for
things that no one has needed yet doesn't seem to fall in line with sound
design.
> (imho of course..)
>
> If you can outline why you need this, and exactly what
properties/conditions you'd want to observe we might be able to work
something out...A general "anything" is harder to understand / design
around.
>
> There is no such thing as a "parameter" property listener because
parameters have no meaning in the context of something taking a
parameter...There has to be a source for that parameter value (usually a
page ) somewhere.
>
> On 10/9/06, Epstein, Ezra <[EMAIL PROTECTED]> wrote:
>
>> Hi Jesse,
>>
>> Thanks for that reply.
>>
>> If I read it correctly, it sounds, simply, like the framework is
>> missing this feature. It's a pretty common thing to ask for listener
>> call-backs on framework events. ("Listener" here in the generic
>> sense rather than the way tapestry uses the term for direct-link
>> targets.) In short, this sounds like a design over-sight. It's
>> common when beans are bound to be able to receive a call-back --
>> Hibernate, for example, offers this. So much of Tapestry seems
>> "automagic" I'm surprised that there's no way to register to be
informed of the events as they occur.
>>
>> If Howard's reading this perhaps he has a better perspective that he
>> may offer.
>>
>> Thanks,
>>
>> Ezra Epstein
>> Amazon.com - Developer Tools
>> 206-266-2259
>>
>>
>> -----Original Message-----
>> From: Jesse Kuhnert [mailto:[EMAIL PROTECTED]
>> Sent: Friday, October 06, 2006 7:22 PM
>> To: Tapestry users
>> Subject: Re: How to observe property binding events
>>
>> Yes, but the usefulness of my answer largely depends on how
>> clever/efficient you are trying to be doing it.
>>
>> Now, there is IBinding. The one object to bind them all ;)
>>
>> If you work your way down the type hierarchy you'll find
>> AbstractBinding, which holds the method you care about most -
>> "setObject". This will be called by tapestry when managing all of the
page properties "automagically"
>> for you.
>>
>> Some of the magic happens in (for your exact case at least)
>> org.apache.tapestry.enhance.ParameterPropertyWorker.
>>
>> The other half of the work happens in each specific binding
>> implementation that will handle these set/get object calls..(Like
>> ognl bindings, etc..)
>>
>> I'm not sure where you are going with this but I guess you could use
>> the hivemind chain of command service sort of configuration (like I
>> did for org.apache.tapestry.services.ComponentRenderWorker ) to
>> generically call a single interface method for a hivemind
>> configuration point...Then you can contribute as many workers into
>> the chain you like if you decide that you have more than one use for
it.
>>
>> Again...Not knowing what you are doing - and taking the exact
>> parameters given I'd probably extend and override the default
>> ParameterPropertyWorker (a hivemind service, so replacing it inline
>> with what Tapestry does already should be easy ) and just override
>> whatever section of code I needed to in that implementation to inject +
call my service reference.
>>
>> It may look a little complicated in there at first, but the whole
>> org.apache.tapestry.enhance package is filled with lots of different
>> enhancement works - and most of them inject a service into the object
>> they work on...So finding an easier to follow worker to reference
>> before modifying ParameterPropertyWorker might be easier.
>>
>> Hope that helps.
>>
>> On 10/6/06, Epstein, Ezra <[EMAIL PROTECTED]> wrote:
>>
>>> I've got a component which accepts a parameter. I want to listen
>>> (receive a callback) when the parameter is set (bound). Does
>>> Tapestry provide such a facility?
>>>
>>> Thanks,
>>>
>>> Ezra Epstein
>>>
>>>
>>>
>>>
>>>
>> --
>> Jesse Kuhnert
>> Tapestry/Dojo/(and a dash of TestNG), team member/developer
>>
>> Open source based consulting work centered around
>> dojo/tapestry/tacos/hivemind. http://blog.opencomponentry.com
>>
>> ---------------------------------------------------------------------
>> To unsubscribe, e-mail: [EMAIL PROTECTED]
>> For additional commands, e-mail: [EMAIL PROTECTED]
>>
>>
>>
>
>
> --
> Jesse Kuhnert
> Tapestry/Dojo/(and a dash of TestNG), team member/developer
>
> Open source based consulting work centered around
> dojo/tapestry/tacos/hivemind. http://blog.opencomponentry.com
>
> ---------------------------------------------------------------------
> To unsubscribe, e-mail: [EMAIL PROTECTED]
> For additional commands, e-mail: [EMAIL PROTECTED]
>
>
>
>
--
Andreas Andreou - [EMAIL PROTECTED] - http://andyhot.di.uoa.gr Tapestry /
Tacos developer Open Source / J2EE Consulting
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Jesse Kuhnert
Tapestry/Dojo/(and a dash of TestNG), team member/developer
Open source based consulting work centered around
dojo/tapestry/tacos/hivemind. http://blog.opencomponentry.com
