Hi Rajesh,
Please do the following in the Select box html code call a javascript which takes the selected value from drop box and based on this Call the
struts Action or what ever you are calling to refresh the Page.
eg
<select name="demo" onChange="refreshPage(this)">
<option value="1"> 1</option>
<option value="2"> 2</option>
</select>
Note this is just an idea that i am providing I dont have any live example to give you right now.
Regards