Question

Why is my List<Date> not getting converted? The <p:selectOneMenu> items pattern looks like
Thu Mar 01 00:00:00 BRT 2012 instead of the desired “MM/yyyy”.

<p:selectOneMenu value="#{report003.selectedMes}">
  <p:ajax update="pesquisaThomas" listener="#{report003.loadPesquisa()}" />
  <f:selectItem itemLabel="[Todos]" itemValue="" />
  <f:convertDateTime pattern="MM/yyyy" />
  <f:selectItems value="#{report003.pesquisaMeses}" />
</p:selectOneMenu>

Answer 1

The conversion applies to the item value only, not to the item label. The label is just presented using the default Date#toString() pattern.

Your best bet is either creating a List<SelectItem> instead of List<Date> wherein you convert the item labels yourself,

List<Date> availableDates = ...;
List<SelectItem> selectItems = ...;
SimpleDateFormat sdf = new SimpleDateFormat("MM/yyyy");

for (Date availableDate : availableDates) {
    selectItems.add(new SelectItem(availableDate, sdf.format(availableDate)));
}

or using <f:selectItems var> with an EL function in the itemValue. For example, the OmniFaces of:formatDate() (or homegrow one).

<f:selectItems value="#{bean.availableDates}" var="date" 
    itemValue="#{date}" itemLabel="#{of:formatDate(date, 'MM/yyyy')}" />

This problem is by the way not specific to <p:selectOneMenu>, you would have exactly the same problem when using the standard <h:selectOneMenu>.