Inject EL Results

[mschmidke]

Hello,

okok, perhaps my yesterday's post was a little bit confusing. I'll give it another try with totally other words.

In Facelets, you can use the ui:include tag to embed components, and you can use ui:param to pass arguments to that components. Inside the included component, the arguments are accessible via EL without any problem, but they are not injectable to seam components. So I suppose that there is some kind of local variable storage in Facelets, which is not accessible from Seam.

I can imagine several solutions for this:

- I am perfectly wrong and there is just a mistake I made somewhere
- Modify Seam so that it can access to that local variable storage
- Add a custom tag which allows to store an EL result in a context variable (so that I can copy them over to something which is visible for Seam)
- Add something else so that I can inject the result of an EL expression

What do you think?

Regards,

Marcus.

[denis-karpov]

You are digging in the wrong direction. Try to design your application in different way. You are trying to couple presentation and business. I assure you that you do not really need this.

[mschmidke]

Maybe wrong direction ... but the last idea I had.

Mixing business and presentation is bad, agreed. But even in Facelets there should be a possibility to write Java code to compute output text.

And in this case, this Java code needs two parameters, no way around. So there's no possibility to write a simple getter to be accessed from EL.

I also tried user defined EL functions. I spent half a day on it, but everything I do is completely ignored. JSTL functions - no problem. User defined functions - no way. Don't know.

So what is the right way to call a Java function and give it the parameters which are available in the component?

[pmuir]

You could preprocess the output [1]. User defined functions (as you mention) are another option. If you have problems with them probably best to post on the facelets user mailing list (they do work as described in the manual).

[1] http://www.jboss.com/index.html?module=bb&op=viewtopic&t=86324

[gavin.king]

So I suppose that there is some kind of local variable storage in Facelets, which is not accessible from Seam.

Yes, ofcourse. This is a definite Good Thing.

[mschmidke]

Yes, ofcourse. This is a definite Good Thing.

Sorry for my stupidity, but I don't understand. The backing bean is part of the view, in this case, and I do not understand why it is not a good idea when the Java part of the view has the same knowledge as the xhtml part of it.

[denis-karpov]

The backing bean is part of the view

No it is not. View connected to the beans by binding expressions. View does not hold references to the beans. In render time, when it is needed to put value in html output it just evaluates binding expression. And then in post time, it evaluates binding expression in another direction to put posted value back to the bean property. There is also method binding for the buttons and links, but it works by the same principles.

Facelets do the great thing. It gives a lot of template capabilities, and it get rid of JSP heritage.

[cptnkirk]

While Seam may not have visibility into facelet's internal variable passing mechanism, isn't this information already present in a JSF or Seam context? How are you passing data as a parameter that didn't originate from somewhere Seam does have access?

[mschmidke]

"CptnKirk" wrote:
How are you passing data as a parameter that didn't originate from somewhere Seam does have access?

Yes ... of course. The data originates from somewhere else in Seam. But since I'm writing a component with reusability in mind, I don't want to worry about the variable name in the caller's scope.

Same as calling methods in plain Java. Inside the method, I don't (want to) know the variable name of the method caller.

String name;
print (name);

public void print(String s) {
 ... at this place I don't want to access "name". This is something I did in my BASIC years.
}

[cptnkirk]

If you want to pass parameters directly via EL I think your only option is to write an EL Function. Everything else in JSF is based on method binding EL which is a simple lookup. Method bindings depend on the bean having all the requisite state prior to invocation.

You could write a custom JSF component that takes in JSF params and communicates directly with your Seam component in Java land.

Or you can have a type specific context aware Seam component. UserManager.printUser(), that knows where to look up the user entity within Seam. This way JSF can take #{user} as a param and your Seam component can use a well known location to function properly.