Drodown using ajax

STEP 1 : 

<aui:select id="region" name="region" label="" cssClass="regionDropdown">

<aui:option value="0" selected="selected">Region</aui:option>

</aui:select>

STEP2 : 

<script type="text/javascript">

window.addEventListener("load", onloadSingleRecord);

function onloadSingleRecord() {

populateAllDropdowns();

}

function populateAllDropdowns() {

var urlAction = "<%=retrieveDropdownListURL.toString()%>";

$.ajax({

      url: urlAction, 

      type: 'POST',

      dataType : "json",

      success: function(result){

      if(result["STATUS"] == "SUCCESS") {

          populateRegionDropdown(result["REGION_DROPDOWN"]);

      }

    }    

  });

}

STEP 3: 

<portlet:resourceURL id="LOAD_DROPDOWN_LIST" var="retrieveDropdownListURL" />

<script>

var retrieveDropdownListURL = '<%=HtmlUtil.escapeJS(retrieveDropdownListURL.toString()) %>';

</script>

STEP 4: 

@SuppressWarnings("static-access")

@Override

public void serveResource(ResourceRequest resourceRequest, ResourceResponse resourceResponse)throws IOException, PortletException {

String resourceId = resourceRequest.getResourceID();

if (null == resourceId || resourceId.isEmpty()) {

resourceResponse.setProperty(resourceResponse.HTTP_STATUS_CODE, "400");

resourceResponse.getWriter().write("This is not a valid request");

return;

}

if (resourceId.equals("LOAD_DROPDOWN_LIST")) {

fetchDropdownListUsingResource(resourceResponse);

} 

/* This is for Region drop down */

function populateRegionDropdown(resultData) {

if(resultData != null) {

var numberOfRows = resultData["REGION_DROPDOWN_ROWS"];

var dropDownObj = document.getElementById("<portlet:namespace/>region");

for(var rowCtr = 0; rowCtr < parseInt(numberOfRows); rowCtr++) {

var option_value = resultData[rowCtr]["RegionPK"] + '@@' + resultData[rowCtr]["RegionName"]

var newRow = new Option(resultData[rowCtr]["RegionName"], option_value);

dropDownObj.options[dropDownObj.length] = newRow;

}

}

}

STEP 5 : 

public static void fetchDropdownListUsingResource(ResourceResponse resourceResponse) throws IOException {

JSONObject json = null;

try {

json = JSONFactoryUtil.createJSONObject();

json.put("REGION_DROPDOWN", getRegionDropdownJSON());

json.put("STATUS", "SUCCESS");

resourceResponse.getWriter().write(json.toString());

resourceResponse.flushBuffer();

} catch (IOException e) {

json.put("STATUS", "FAILED");

resourceResponse.getWriter().write(json.toString());

resourceResponse.flushBuffer();

_log.error(e.getMessage());

}

}

STEP 6 : 

private static JSONObject getRegionDropdownJSON() {

JSONObject dropdownJson = JSONFactoryUtil.createJSONObject();

JSONObject rowData = null;

List<VwTcDropdownLists> listObj = VwTcDropdownListsLocalServiceUtil.getRegionDropDown();

if (listObj != null && (!listObj.isEmpty())) {

dropdownJson.put("REGION_DROPDOWN_ROWS", "" + listObj.size());

VwTcDropdownLists beanObj = null;

for (int i = 0; i < listObj.size(); i++) {

beanObj = listObj.get(i);

rowData = JSONFactoryUtil.createJSONObject();

rowData.put("RegionPK", "" + beanObj.getItemTreePosition());

rowData.put("RegionName", "" + beanObj.getItemName());

dropdownJson.put("" + i, rowData);

}

} else {

dropdownJson.put("REGION_DROPDOWN_ROWS", "" + 0);

}

return dropdownJson;

}