TAsPectJ

[Erik Hatcher <er...@ehatchersolutions.com>]

At OSCON (O'Reilly Open Source Convention) this past week, I had the 
pleasure of attending Raminvas Laddad's excellent AspectJ tutorial.  
While I've kept in the loop of what AOP is all about, I had not 
actually tried it (other than pseudo XDoclet, WebWork2, and dynamic 
proxy types of things), I'm a bit ashamed to report.

During my travel to OSCON, I finally started reading Raminvas' AspectJ 
in Action book, and have only made it through the first section 
explaining the concepts and syntax.

The night before the tutorial I downloaded AspectJ and tried a simple 
HelloWorld kinda thing to make sure I had the necessary pieces to 
leverage the goodies I'd learn in the tutorial.  Half-way through his 3 
hour session, I had enough infrastructure in place to aspect the demo 
Tapestry application I use for my presentations.  The one feature that 
has bothered me about Tapestry is its difference with what happens when 
validation fails compared to Struts.  When validation fails, the 
listener method is still called in Tapestry, and this requires a bit of 
code to handle it *in every single listener method*.  While I'm still 
on the fence on whether Tapestry should itself avoid calling a form 
listener method when validation fails, in the apps I build it is always 
the case.  AspectJ came to my rescue.  I created this aspect...

public aspect ValidationAspect {
     void around(BasePage page) : execution(void 
Home+.listener(IRequestCycle)) && this(page) {
         ValidationDelegate delegate = (ValidationDelegate) 
page.getBeans().getBean("delegate");
         System.out.println("aspected: " + delegate);

         if (!delegate.getHasErrors()) {

           proceed(page);

         }
     }
}

Disclaimer: Home+.listener is specific to my code - I need to tinker 
with the point cut definition to make it more general purpose - so if 
you borrow this idea, you'll need to change that part at least.  Using 
a cflow or cflowbelow is probably the next refactoring I'll try to key 
off the call chain through @Form for invoking a listener method, but 
that won't catch @Submit listeners (which I personally avoid anyway).

Voila - I now keep my form listener methods devoid of the validation 
concern (unless of course there is programmatic validation needed as 
well, but this is far less common in my apps than straightforward field 
validation).

I really wish Tapestry had an intermediate hook between a form 
submission and the invocation of the listener method built-in, though 
(and geez, you'd think Page*Validate*Listener is the right hook, but 
it's not).  AspectJ really solved the issue I have been frustrated 
with, so I'm now smiling!  In fact, being able to pull this trick off 
after only brief exposure to AspectJ has left me grinning all week and 
is a great case in point regarding the power and ease of use of AOP in 
general.

	Erik

p.s. Immediately following the AspectJ tutorial, I gave my Tapestry 
tutorial to a sold-out crowd, and mentioned my AOP success that 
morning.  Many folks lingered after my presentation, and I was able to 
show off my success to them.



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Re: Tapestry on CD/Offline

[Cyril Godefroy <cy...@ecomposite.fr>]

Makes sense. A typical solution might be:
Jetty as the web app container
Hsqldb as the database (in memory version)

but then, you might even use struts or jsf. Tapestry won't bring you 
anything special in that regard ( it does already for many other 
aspects).

Cyril
On Aug 2, 2004, at 3:27 PM, tibolists wrote:

> then launching the Tapestry app, include launching a embedded web
> application server.
>
> Is that make sense ?

Re: Tapestry on CD/Offline

[tibolists <ti...@free.fr>]

What I wanna mean by "Offline",
is: not connected to the net.

Well, in fact, the goal, is to have a tapestry app, work as a standalone
program.

even if the user's computer do not have a webserver and anything else
the OS installed on it.

then launching the Tapestry app, include launching a embedded web
application server.

Is that make sense ?



On Mon, 2004-08-02 at 13:47, Erik Hatcher wrote:
> What do you mean by "offline"?   You need a web container.... so at the 
> minimum you need something like Jetty and a way to launch it.  I'm sure 
> you could wrap it all into a single launchable JAR file that can be 
> double-clicked and even open up the default browser.  ZOE (zoe.nu) does 
> this type of thing.
> 
> 	Erik
> 
> On Aug 2, 2004, at 7:49 AM, tibolists wrote:
> 
> > HI,
> >
> > Is there any way to have a fully tapestry app, work on CD,
> > or even work offline from harddisk ?
> >
> > tibo
> >
> >
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> 


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Re: Tapestry on CD/Offline

[Erik Hatcher <er...@ehatchersolutions.com>]

What do you mean by "offline"?   You need a web container.... so at the 
minimum you need something like Jetty and a way to launch it.  I'm sure 
you could wrap it all into a single launchable JAR file that can be 
double-clicked and even open up the default browser.  ZOE (zoe.nu) does 
this type of thing.

	Erik

On Aug 2, 2004, at 7:49 AM, tibolists wrote:

> HI,
>
> Is there any way to have a fully tapestry app, work on CD,
> or even work offline from harddisk ?
>
> tibo
>
>
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Tapestry on CD/Offline

[tibolists <ti...@free.fr>]

HI,

Is there any way to have a fully tapestry app, work on CD,
or even work offline from harddisk ?

tibo


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