I'd suggest using a combination of the <logic:iterate> tag or <c:forEach> if you prefer, and the <html:multibox> tag. Example:
Suppose you have a HashMap that contains a bunch of sectors for which each entry contains the sector id as the key and the sector name as the value, and that the hashmap is stored in request scope under the name "sectors". The following code would work:
When the user submits this form, your ActionForm's property "selectedSectors" will be a String array containing all the selected sector IDs.
See the heading "multibox" in this link for more information on the multibox tag.