JSF c:forEach vs ui:repeat

<h:dataTable values="${numbers}" var="number">
  <h:column>
    <c:if test="${number > 5}">
      <h:outputText value="${number}"/>
    </c:if>
  </h:column>
</h:datatable>

<ui:fragment rendered="${number > 5}"> ... </ui:fragment>

<ui:repeat value="#{bean.items}" var="item">
   <ui:include src="#{item.src}"/>
</ui:repeat>

myTag.xhtml:

<ul>
  <ui:repeat value="${item.children} var="child">
    <li><eg:myTag item="${child}"/></li>
  </ui:repeat>
</ul>

<h:form>
  <c:forEach items="${list}" var="item">
    <h:outputText value="${item.name}"/><br/>
  </c:forEach>
  <h:commandButton value="Create new item" action="..."/>
  <h:commandButton value="Delete an item" action="..."/>
</h:form>

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Really great post. (Y)

 hello I have a ,question it took days to estrus trabajndo with jfs and I have the following code inside a foreach q I list the questions and alternatives interrgante database is like saving my questions answered

Great blog, dude, building a deeper understanding of important details. Thanks!

Best regards.

Glad you found it helpful Cliff. Don't forget to share to your favorite social network..

 Just stumbled upon this as I was struggling with c:foreach, excellent write up.  Thank you!

THANKS FOR THIS BLOG DUDE!!! It helped me ;)

 Thanks. c:forEach inside dataTabe took long time to find issue..  going to drop considering iceface 

 Thx for the blog, I was trying to build a sample application with a beta of jsf 2.0 and I ran into some this problems so quick.

It's really confusing for someone who is starting with jsf and you wont find this problems in all of those "quick cool ajax component in jsf 2.0" guides....

I just want a framework that has databinding, converters, validators and easy component creation, but I think all this is too much for me, I will never convince my colleagues if I have to explain all the problems you have to run into:

phase listeners, the whole encode/decode process, you have to know the component tree, bookmarking is not easy (there is no way to submit a form with nice get parameters ...)

I was really disappointed with jsf 1.2, and it seems that jsf 2.0 has more nice features, but you still have to run into many many WTF's.

what a load of crap another java special; jstl/core does the trick !!! care to explain? consider ui:include where's the rendered there - an obvious lack of planning there

Hi,

Can someone explain this as I am a bit baffled?

If I use the old JSTL 1.0 tag library I can create a set of dynamic tabs using c:forEach, but if I use the newer JSTL 1.1 version it does not work.

For example:

`
<a4j:commandButton id="search" value="Search"
action="#{myBean.searchEvents}" reRender="myTabs" />

<rich:tabPanel id="myTabs" switchType="ajax">
  <c:forEach items="#{myBean.getEvents()}" var="_event">
    <rich:tab label="#{_event.name}" >
    </rich:tab>
  </c:forEach>
</rich:tabPanel

`

The above works fine if I include the following JSTL tag library (JSTL 1.0 - J2EE 1.3/JSP1.2):-

`
xmlns:c="http://java.sun.com/jstl/core"
`

However, if I include the following JSTL tag library it does not work (JSTL 1.1 - J2EE 1.4/JSP 2.0):-

`
xmlns:c="http://java.sun.com/jsp/jstl/core"
`

I am using the \#{} deferred EL syntax, however, it looks that when I am using the newer version that it is trying to evaluate the myBean.getEvents() before the events are actually populated by the submission of the Search button.

I am concerned that I am introducing a dependency on a old version of the JSTL library.

I am using JBoss 5.1.0 with Seam 2.2.

No, rich:tabPanel with a c:forEach in it works. But if I add another tab, all are fully rerenderd. That is something I try to prevent now.

<rich:tabPanel> probably expects all its children to be <rich:tab>s and simply ignores the <a4j:repeat> component.

Hi,

I get most of what you are saying, but I can't for the life of me figure out why this works (i.e. creates a set of tabbed panels with one tab each):

<a4j:repeat value="#{myAction.events}" var="_event">
        <rich:tabPanel>
                <rich:tab label="#{_event.name}">
                </rich:tab>
        </rich:tabPanel>
</a4j:repeat>

and this doesn't (i.e. should create a set of tabs within a single tab panel)

<rich:tabPanel>
     <a4j:repeat value="#{myAction.events}" var="_event">
                <rich:tab label="#{_event.name}">
                </rich:tab>
    </a4j:repeat>
</rich:tabPanel>

My understanding is that the a4j:repeat is a component (similar to the ui:component), the rich:tabPanel is a component, and the rich:tab is a component.

Btw, the above code snippet is wraped in a repeating simpletogglepanel (created via a a4j:repeat) so I can't use c:forEach to create them.

Anyone tried to use really use <ui:include> ? How do you manage your id`s

Atm i have problems inside a loop and with using the templates at different locations (e.g. address template for customer main and secondary address) . For this i need to validate a little bigger context as only on field level scope.

Any examples out there how to solve such problems ? 

Hi,

I have created a list of files to download using ui:repeat.

I would like to know how can i know which element has been clicked from the list. This list can be different.

<ice:panelGroup>
<ui:repeat value="#{recursos.itemList}" var="item">
<h:panelGroup rendered="#{item.type== 'pdf'}">
<ice:outputText value="#{item.label}" />
<br />
<ice:outputResource id="pdfResource1"
label="#{msgs['download']}"
resource="#{resourceBean.pdfResourceDynFileName}"
mimeType="application/pdf" fileName="#{item.label}"
attachment="true" shared="false" style="width:150px" />
</h:panelGroup>
</ui:repeat>
</ice:panelGroup>

Any suggestions.

thanks

JSF 2.0 (with Facelets within) goes further in confusing developers.

Personally I consider mixing expression with different execution time in one context as a bad design, which is innate nature of facelets and JSF. JSF is sophisticated framework, what means its design is too complicated for static HTML (and a source of unacceptable overhead) and is not ready for dynamic Web.

JSF suxx. Try to get rid of it. As it said Java community is in demand of the next brand new framework.

 

Does <c:forEach> can be used in XHTML?

Thanks for the post.  Just cleared up the if statement gotcha for us.

I agree on the confusing aspect of this.  Facelets should have a "gotchas" page.  The fact facelets has core tags is very enticing in terms of its adoption.  It's disappointing when it doesn't behave like we expect, no matter what the reason.

Classic rule of least surprise.

If java wasn't inventing framework one after the other, .NET would not have nHibernate, nUnit, and so on ... So keep your comments to yourself

I dont understand why do you use facelets and use a "new weird xml language".Yeah .. sure ...it looks elegant..  But at what cost..confusion.. debugging issues..

The problem is Java guy keep on inventing framework one after another..

Instead of focussing on providing GOOD GUI IDE(like in .net)..

.NET does not use this weird XHTML and "new tag language"

Another resource on the subject:

andrewfacelets.blogspot.com/2008/03/build-time-vs-render-time.html

Yeah thats what i wanted to do. Problem is by architechtural choice, we are not allowed.

After further investigation, my root call <mytag:menu get called 37 times and it stop growing. This is so weird, and wrong in every way, but at least, it doesn't do a stack overflow :)

Hey Rouche, your code looks good to me. I've done exactly the same thing before. FWIW, you might be better off coding this one as a Java UIComponent. It is quite simple and you will get much better performance.

Im new to Facelets, ive been able to make a menu working but it seems like the recursive nature of my facelet makes the evaluation stack grow to stellar size. Ive been working on this since one week without success.

leftmenu.xhtml (This is the initiate call, the navigationMenu is inside a spring config)

        <t:div id="left_menu">
            <mytag:menu menuItems="#{navigationMenu.navigationItems}"/>
        </t:div>

fragment menu.xhtml

    <ul class="#{styleClass}">
    <c:forEach var="item" items="#{menuItems}">
        <c:choose>
            <c:when test="#{item.open}">
                <li class="ouvert"><a href="#">#{item.label}</a></li>
                <mytag:menu menuItems="#{item.navigationItems}" styleClass="submenu"/>
            </c:when>
            <c:otherwise>
                <li><a href="#{facesContext.externalContext.requestContextPath}#{item.action}.iface">#{item.label}</a></li>
            </c:otherwise>                           
        </c:choose>
    </c:forEach>
    </ul>
I really hope there is a solution to this, i caint think this is not possible.

I think Tomahawk's t:dataList will do that for you.

Sorry, previous post are mistkenly added. Please ask for confirmation on pressing enter. Ajax is good but, confirmation allows user to  fix/correct the message.

Here is my question:

<c:forEach> in jsp's jstl supports varStatus with index count and it also supports key/value for map type. for e.g

<c:forEach var='item' items='${map}' varStatus="status">
     <c:out value="${item.key}" /><c:out value="${item.value}"

  <c:if test="${status.index}" >
  </c:if>

</c:forEach>

I need to do same using UI:repeat. I found that UI:repeat iterates perfectly but does not provide us the index var as well as key/value for map item.
Please help.

<ui:fragment rendered="${number > 5}"> ... </ui:fragment>

no longer appears to be a viable suggestion because "rendered" is no longer a valid attribute.

"c:forEach" does not seem to work with "ui:include" either. The code below produces a stack trace:

<c:forEach var="x" items="#{mainToolBar.include}">
<ui:include src="#{x}"/>
<c:forEach/>

Thank you very much for this guide!!!

You can use an ui:include inside ui:repeat, but it is only included once, in a similar way to JSP's <%@ include %> directive. The problems arise when you want a dynamic include which changes for every iteration of the loop. You must use c:forEach in this case.

Glad to have found this page. We were struggling with the "My ui:include fails inside ui:repeat" issue described here. Re-writing it to use c:forEach seems to have resolved the issue, but has resulted in performance problems, perhaps just as described by "roger" on 23 July 2007. We have made extensive use of the component architecture using ui:include and ui:decorate. Unfortunately these are frequently used in the context of a loop, with the templates being nested a few levels deep. Based on my limited understanding of the situation, we can only re-use these template components inside a loop via the forEach style loop with the associated run-time costs. There does not appear to be any re-usable faclet components which can be used inside of the ui:repeat loop. Is this a correct (if somewhat simplistic) summary of the situation? Can anyone point me to a re-use template pattern using Facelets that works with ui:repeat? As it stands we appear to be in a situation where we have to live with very poor performance or we must give up the nice re-use that we have in place. I would be happy to provide more concrete examples if anyone has input or suggestions.

For newbies (like me) it would help if someone could add examples of what pages with these types of problems look like. All the textual discussion about the mechanics of what's going on is important, but there's nothing like picture to make things obvious.

Facelets treats both deferred and immediate EL expressions the same (deferred according to the definitions on that page). Using the #{} notation with c:forEach doesn't imply that the expression is evaluated at any specific time. In fact, in the case of c:forEach, expressions are evaluated whenever they are referenced, which can also trip you up sometimes. For example, if you had

<c:forEach items="#{dao.query}" var="item"> ... </c:forEach>

Every evaluation of #{item} is rewritten to #{dao.query[x]} and reevaluated, possibly leading to poor performance (blog about this coming soon ). It is all still done during build time though and never actually 'integrates with components'. Apparently the JSP version is different (?).

The performance hit due to reevaluation doesn't apply for ui:repeat because that component is written to store it's value locally. But even components can evaluate their value attribute several times during the lifecycle... it's really up to the author of the component.

Thank you for your reply. I guess I am referring to the Unified Expression Language, which introduces deferred evaluations to EL (evaluation during the JSF lifecyle). See http://java.sun.com/products/jsp/reference/techart/unifiedEL.html. That seems to alter the distinction you are making somewhat, since c:forEach, for example, is still a tag handler but will integrate with components. What's interesting about your article is that even some native facelets tags act as tag-handlers. This has certainly not been well-documented until now.

Hi Ed. JSF 1.2 has better integration of JSTL and JSP. This article is specific to Facelets which works just the same on JSF 1.1 and JSF 1.2, so everything here applies to both versions.

With regard to Mike's comment: not all converters/validators work the same way as the JSF Core converters/validators. All the Trinidad converters/validators run at component time, so they are free to depend on a component iterator.

And, as you mentioned, validators and converters are another story.   For instance, we just had an issue show up on the MyFaces user mailing list because the jsf core converters only evaluate their el expressions on creation, not during any other time.   So making a jsf core converter value binding depend on a component iterator (dataTable, ui:repeat, etc) is impossible.