I have a composite component and this is a snippet from it.
<h:outputFormat id="output" value="{0} / {1} / {2}" rendered="#{cc.attrs.readOnly}" styleClass="#{cc.attrs.styleClass}">
<f:param value="#{empty cc.attrs.value1 ? '-' : cc.attrs.value1}" />
<f:param value="#{empty cc.attrs.value2 ? '-' : cc.attrs.value2}" />
<f:param value="#{empty cc.attrs.value3 ? '-' : cc.attrs.value3}"/>
</h:outputFormat>
If I want to format value3 using <f:convertNumber>, how can I do that?
<h:outputFormat> uses under the covers standard java.text.MessageFormat API. Go ahead clicking that link and reading the javadoc.
<f:convertNumber> uses under the covers the standard java.text.NumberFormat API which happens to be supported by MessageFormat as well. As its javadoc says, numeric patterns can be represented by {[index], number, [pattern]}.
Thus, so (this example assumes that you want 2 fixed-length fraction digits):
<h:outputFormat id="output" value="{0} / {1} / {2,number,#.00}" rendered="#{cc.attrs.readOnly}" styleClass="#{cc.attrs.styleClass}">
<f:param value="#{empty cc.attrs.value1 ? '-' : cc.attrs.value1}" />
<f:param value="#{empty cc.attrs.value2 ? '-' : cc.attrs.value2}" />
<f:param value="#{empty cc.attrs.value3 ? '-' : cc.attrs.value3}"/>
</h:outputFormat>