If your combo box is multiple select : 
Declare one array  String variable in your action.And that
variable name should match with the combo box name. Then you
will get all the selected values into your action. There you
pass those variable to your DAO. 

If your combo box is single select you can directly declare
a variable in your action as the same name with combo box.

Sarath

Hi friends, What i feel is..... 
    The above answer is partially correct.sharath has taken 
only 2 things(multiple select and single select) into the 
considaration, I think along with with those to we hav to 
take one more thing(UI tag <s:checkbox/> or 
<s:checkboxlist/> ) what we are using in the User interface 
into considaration while giving the answer.

When we are using  <s:checkboxlist/> tag in the usr 
interface for displaying the Checkbox(s) , the Data type in 
our struts2 action is List.


Thank you friends