function init() {
var arr = new array();
<%
String[] piatti = request.getParameterValues("piatti"); //<---debugging "piatti" has 3 values
if (piatti != null) {
  for (int i=0; i<piatti.length; i++) { //<--- this for is actually done 3 times
    %>
    arr[<%=i%>] = <%=piatti[i]%>;
    alert("ciao") //<--- even if debug pass from this one, i have no alert window :(
    <% } 
  } %>
  var j = 0;
  for (j=0; j<arr.length; j++) { //<--- this for is done only 1 time
    if (document.ins_risto.piatti.options[j].value == arr[j]) {
      document.ins_risto.piatti.options[j].selected = true;
    }
  }
}