What is the real conceptual difference between ui:decorate and ui:include?
Solution 1:
The main difference between <ui:include>
and <ui:decorate>
is that the <ui:decorate>
is intended to allow insertion of user-defined template components, while the <ui:include>
is intended to include an existing and already-predefined template.
This indeed means that the <ui:decorate>
supports <ui:define>
for user-defined template components in its body and can insert it at the <ui:insert>
place inside the template.
Here's a -somewhat clumsy- example to show where it can be used:
/WEB-INF/templates/field.xhtml
<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:outputLabel for="#{id}" value="#{label}" />
<ui:insert name="input" />
<h:message id="#{id}_message" for="#{id}" />
</ui:composition>
/page.xhtml
<h:panelGrid columns="3">
<ui:decorate template="/WEB-INF/templates/field.xhtml">
<ui:param name="label" value="Foo" />
<ui:param name="id" value="foo" />
<ui:define name="input">
<h:inputText id="foo" value="#{bean.foo}" required="true" />
</ui:define>
</ui:decorate>
<ui:decorate template="/WEB-INF/templates/field.xhtml">
<ui:param name="label" value="Bar" />
<ui:param name="id" value="bar" />
<ui:define name="input">
<h:selectBooleanCheckbox id="bar" value="#{bean.bar}" required="true" />
</ui:define>
</ui:decorate>
...
</h:panelGrid>
Note that it renders the components nicely in each cell of the panel grid. Again, this particular example is pretty clumsy, I'd just have used a tag file instead. Only if it was a larger section, e.g. a whole form whose e.g. its header or footer should be customizable, then an <ui:decorate>
would have been appropriate.
Another major advantage of <ui:decorate>
is that it allows you to use a composite component with a template. See also Is it possible to use template with composite component in JSF 2?