Why doesn't h:commandButton execute the action method when combined with c:chose? - jsf

Question

I've seen a strange problem in my project. It's that <h:commandButton/> does not execute the action method.
<c:choose>
<c:when test="#{empty param.t}">
// HTML
</c:when>
<c:when test="#{param.t eq 'normal'}">
// HTML
<h:form>
<h:commandButton value="ADD" action="#{addBean.doSomething}" />
</h:form>
<c:when>
</c:choose>
When I move <h:form> into first c:when, then the action method is called. Otherwise, it isn't. Why?

Answer 1

I'll ignore the syntax error in your EL (a missing }).
The command button won't be executed when #{param.t eq 'normal'} evaluates to false at the point the form submit request is to be processed. You need to maintain the same parameter for the subsequent request so that the button will be rendered so that JSF can confirm that the enduser is allowed to invoke the action. You can do this by adding a <f:param>:
<h:form>
<h:commandButton value="ADD" action="#{addBean.doSomething}">
<f:param name="t" value="#{param.t}" />
</h:commandButton>
</h:form>
Note that this is supported since JSF 2.0 only. On JSF 1.x you'd need to replace h:commandButton by a h:commandLink if you want f:param support.
Unrelated to the concrete problem, you should try to avoid JSTL as much as possible in your JSF views. If the intent is to render view parts conditionally (not to build view parts conditionally), then you should rather be using the JSF component's rendered attribute instead of a JSTL <c:choose> or <c:if>:
<h:panelGroup rendered="#{empty param.t}">
// HTML
</h:panelGroup>
<h:panelGroup rendered="#{param.t eq 'normal'}">
// HTML
<h:form>
<h:commandButton value="ADD" action="#{addBean.doSomething}" />
</h:form>
</h:panelGroup>