Forms dropdown selection changed

hi 

We are using CQ Forms which has multiple dropdowns. On Selection of Country, the States should populate, on selection of state, city should populate. All the values in the 3 dropdowns are populated from external database.

How can we call Jquery Ajax call to servlet to populate the Country dropdown on page load and hencforth on selection of each dropdown making Ajax call.

Can the selection xtype "options"  be linked to a servlet returning JSON array - like /apps/example/myservelt.json which returns the list of Countries on Load of the form?

Similarly rather calling a javascript function on selectionchanged event of Country dropdown can we call a servlet returning JSON list of States?

Any pointers would be helpful