Avoiding duplicate ids when reusing facelets compositions in the same naming container

Question

I have a <ui:composition> that contains a few elements with explicit ids and some ajax events which reference these ids for partial processing/updating. I encapsulated this fragment of xhtml inside the composition simply so I could use it in a few different places without having to duplicate the code. However, when I use the composition (with <ui:include>) more than once inside a page, I get duplicate id exceptions. It seems JSF is not wrapping each composition inside its own naming container (like <ui:component> does).

Is there a simple way to wrap my composition inside its own naming container? Or do I have to use a composite component every time I want to reuse xhtml fragments inside a common naming container?

Answer 1

Depending on the purpose of the <ui:include> template, you've several options:

1. Use <f:subview>. It creates another NamingContainer context (like as <h:form>, <h:dataTable>, and friends all do):

   <f:subview id="top">
       <ui:include src="/WEB-INF/includes/some.xhtml" />
   </f:subview>
   ...
   <f:subview id="bottom">
       <ui:include src="/WEB-INF/includes/some.xhtml" />
   </f:subview>
   

   The components definied in some.xhtml will end up getting respectively top: and bottom: prefix in their ID.

   ---

2. Turn it into a tagfile which requires an id attribute.

   <my:some id="top" />
   ...
   <my:some id="bottom" />
   

   And use that ID to prefix the ID of the components in the composition.

   <ui:composition 
       xmlns="http://www.w3.org/1999/xhtml"
       xmlns:f="http://java.sun.com/jsf/core"
       xmlns:h="http://java.sun.com/jsf/html"
       xmlns:ui="http://java.sun.com/jsf/facelets"
   >
       ...
       <h:someComponent id="#{id}_some" />
       <h:otherComponent id="#{id}_other" />
       ...
   <ui:composition>
   

   ---

3. Turn it into a composite component. Composite components are inherently already a NamingContainer, so their id attribute is optional. Basically, replace

   <ui:composition 
       xmlns="http://www.w3.org/1999/xhtml"
       xmlns:f="http://java.sun.com/jsf/core"
       xmlns:h="http://java.sun.com/jsf/html"
       xmlns:ui="http://java.sun.com/jsf/facelets"
   >
       ...
   <ui:composition>
   

   by

   <ui:component 
       xmlns="http://www.w3.org/1999/xhtml"
       xmlns:f="http://java.sun.com/jsf/core"
       xmlns:h="http://java.sun.com/jsf/html"
       xmlns:ui="http://java.sun.com/jsf/facelets"
       xmlns:cc="http://java.sun.com/jsf/composite"
   >
       <cc:interface>
           <!-- This is optional. -->
       </cc:interface>
       <cc:implementation>
           ...
           <h:someComponent id="some" />
           <h:otherComponent id="other" />
           ...
       </cc:implementation>
   <ui:component>
   

   This way you can use it as follows:

   <my:some id="top" />
   ...
   <my:some id="bottom" />
   

   The components definied in <cc:implementation> will end up getting respectively top: and bottom: prefix in their ID (note again, the composite component's id attribute is optional, JSF will otherwise autogenerate one).

   ---

See also:

• When to use <ui:include>, tag files, composite components and/or custom components?

Answer 2

When you include more than once the same ui:composition the id are duplicated. The solution is to specifiy a particular ui:param within the ui:include.

Assuming you're including mycomposition.xhtml you can do something similar:

<ui:include src="mycomposition.xhtml">
    <ui:param name="idPrefix" value="first"/>
</ui:include>

...

<ui:include src="mycomposition.xhtml">
    <ui:param name="idPrefix" value="second"/>
</ui:include>

Then in the mycomposition.xhtml you should declare the ids as follows (for instance a h:outputText):

<h:outputText id="#{idPrefix}_text" value="My Awesome Text here"/>

Now you can reference the id in the rest of yout page as #{idPrefix}_text.