Dynamically setting value of a h:selectOneMenu using c:forEach - jsf

Question

I'm working on a project that requires me to display and be able to select and store tags to the product. Tags are provided in tree-like structure. I can't assume maximum depth of a tags tree.
I wanted to display tags split by levels, using c:forEach - p:selectManyCheckbox - f:selectItems, and handling selections using p:ajax components.
I use following types to store possible values and selections in Tree object:
HashMap<Long, ArrayList<Tag>> tree;
HashMap<Long, Object[]> selected;
Hashmap keys are equal to "tag level".
In order to display values I use following code for testing:
<p:panelGrid id="tagDisplay" columns="2">
<c:forEach begin="1" end="5" var="idx">
<p:outputLabel value="#{idx}"></p:outputLabel>
<p:selectManyCheckbox value="#{product.tags.selected[1]}">
<f:selectItems value="#{product.tags.tree[1]}" var="tag" itemLabel="#{tag.name}" itemValue="#{tag.id}" />
<p:ajax listener="#{product.selectorListener}" update="tagDisplay" />
</p:selectManyCheckbox>
</c:forEach>
</p:panelGrid>
Code seemed to work fine, though displayed five times.
Now I'm stuck trying to dynamically bind Hashmaps to selectors. As I replaced "1" with "idx", I got no results.
I tried to use ui-repeat with a dummy table, but then I lost panelgrid structure.
Any help will be appreciated!
My environment - Websphere 8.5, JSF 2.2, Primefaces 5.2

Answer 1

The <c:forEach begin end> is only for static iteration, not for dynamic iteration.
You'd better iterate over #{product.tags.tree} itself in <c:forEach items>. Each iteration over a Map will give Map.Entry back which in turn has getKey() and getValue() methods.
<p:panelGrid ...>
<c:forEach items="#{product.tags.tree}" var="entry" varStatus="loop">
<p:outputLabel value="#{loop.index}"></p:outputLabel>
<p:selectManyCheckbox value="#{product.tags.selected[entry.key]}">
<f:selectItems value="#{entry.value}" ... />
...
</p:selectManyCheckbox>
</c:forEach>
</p:panelGrid>
That said, must it really be a HashMap? Don't you rather want a fixed ordered LinkedHashMap?