JSON with AJAX

Example shown to use AJAX and JSON to dynamically populate a dropist.
When droplist 1 is changed, droplist 2 get refreshed with data sent from the server through an AJAX call in a JSON format.

Droplist 1
<html:select property="personCode" onchange="getPersonType();">
<html:option value="" > </html:option>
<html:options property="personCodeList"/>
</html:select>

Droplist 2
<html:select property="personType">
</html:select>


<script>

function getPersonType()
{
var selBox = document.personViewForm.personCode;
var personCode = selBox.options[selBox.selectedIndex].value;
var url = "/Orion/ajax.do?method=getPersonType&personCode="personCode;

var jsonReq = new Json.Remote(url, {
async: false,
autoCancel:true,
onComplete : function(personTypeList){ populatePersonType(personTypeList);
}}).send();
}


function populatePersonType(personTypeList)
{

var selBox = document.personViewForm.personType;
selBox.options.length = 0 ;
selBox.options[0] = new Option("", "");

for(i=0, len=personTypeList.length ; i<len ; i++)
{
selBox.options[i+1] = new Option(personTypeList[i], personTypeList[i]);
}
}

</script>

import net.sf.json.JSONArray;
import org.apache.struts.action.Action;

public class AjaxAction extends Action
{
public ActionForward execute(ActionMapping mapping, ActionForm form, HttpServletRequest request, HttpServletResponse response)
throws Exception {

// this Action is not mapped to a form and does not use a JSP for view,
// thus form and mapping and not neccessary

try {
String method = request.getParameter("method");

if("getPersonType".equals(method))
{
doGetPersonType(request, response);
}
else{
// send an error if "no such method"
doTheExceptionThing(request, response);
}

} catch (Exception ex) {
doTheExceptionThing(request, response);
}
return null;
}

private void doGetPersonType(HttpServletRequest request, HttpServletResponse response)
throws IOException
{
String personCode = request.getParameter("personCode");

List<String> list = DatabaseHelper.getPersonTypeList(personCode);

JSONArray array = JSONArray.fromObject(list);
String s = array.toString();

response.setContentLength(s.length());

PrintWriter output = response.getWriter();
output.print(s);

output.close();
}

private void doTheExceptionThing(HttpServletRequest request, HttpServletResponse response) throws Exception {

// since this action is used by a background Javascript invocation, there's not much error to be sent
// or seen by the client. We'll just send a generic error message.

response.setContentType("text/xml");
response.setHeader("Cache-Control", "no-cache");
response.getWriter().write("error");

}

}

Required libraries - json-lib-2.1-jdk15.jar, mootools.js