Struts2 increment a previous set <s:set /> value

You aren't required to create a reference variable just use #i.index or #i.count inside the iterator. It's already incremented by the iterator tag itself.

Note that "count" is 1-based, "index" is 0-based.

Always check the docs.

If you still need your own counter

<s:set var="counter" value="0"/>

increment

<s:set var="counter" value="%{#counter+1}"/>