How to Default a value in dynamic list (s:select)

[Raghuveer Rawat]

Hi, How to make a value as default value in a dynamic list s:select?
Below code display a List of Countries sorted by Country Name so country
name with letter a comes first but I want USA as default country.
How to do that?

 <s:select name="user.country" headerKey="-1" headerValue="Select Country"
                            list="countryList" listKey="code"
listValue="name" required="true" />

Thanks...