Dynamic dropdowns using thymeleaf, spring boot

Question

I have 3 dropdowns(one is populate with cities, one with agencies and one with services). If I select one city, the second dropdown should load the data(agencies), and if i select one agency, the 3 dropdown should load data(services). I am able to populate the first dropdown(cities), but I don't know how to populate the second and third.

Should i write a controller for each dropdown and return the value? If the answer is yes, how can I return the value? I've read that Thymeleaf is not a component technology but a template technology like JSP. So there is not components or built-in mechanism in Thymeleaf to do client-server communication. So I need to program that communication using plain old HTML forms or using AJAX calls. How can I program it using plain old HTML?

I tried using forms, but I click submit only once, it is not what I need. I read the posts about dropdowns, but couldn't find anything helpful. I saw that the easy way is to use jQuery, but I don't know jQuery. Is there a way I can do this using only thymeleaf and spring boot? Thanks! I will post my code below.

appointment.html

<form th:action="@{/appointment/create}" method="post" id="appointmentForm">
            <input type="hidden" name="id" th:value="${appointment.id}"/>
<div class="form-group">
                <label for="location">Alege orasul:</label>
                <select class="form-control" required="required" 
th:value="${appointment.location}" name="location" id="location">
                    <option disabled="disabled" selected="selected" > -- 
alege orasul --</option>
                    <option th:each="city : ${cities}" th:value="${city.id}" 
th:text="${city.name}" ></option>
            </select>
            </div>
            </form>

            <form th:action="@{/appointment/agency}" method="post" id="appointmentForm">
            <input type="hidden" name="id" th:value="${appointment.id}"/>
            <div class="form-group">
                <label for="location">Alege agentia:</label>
                <select class="form-control" th:value="${appointment.agency}" name="agency" id="agency" required="required">
                    <option disabled="disabled" selected="selected" > -- alege agentia --</option>
                    <option th:each="agency : ${agencies}" th:value="${agency.id}" th:text="${agency.name}" ></option>

                </select>
            </div>
            </form>
            <form th:action="@{/appointment/service}" method="post" id="appointmentForm">
            <input type="hidden" name="id" th:value="${appointment.id}"/>
            <div class="form-group">
                <label for="location">Alege serviciul:</label>
                <select class="form-control" th:value="${appointment.service}" name="service" id="service" required="required">
                    <option disabled="disabled" selected="selected" > -- alege serviciul --</option>
                    <option th:each="service : ${services}" th:value="${service.id}" th:text="${service.name}" ></option>

                </select>
            </div>
            </form>

AppController.java

@Controller
@RequestMapping("/appointment")
public class AppointmentController {

@Autowired
UserService userService;    
AppointmentService appointmentService;  
CityService cityService;
AgencyService agencyService;
SerService serService;
private ModelAndView mav;

@RequestMapping(value="/create", method=RequestMethod.GET)
public String createAppointmentPost(Model model, @ModelAttribute("city") City 
city, @ModelAttribute("agency") Agency agency){


    Appointment appointment=new Appointment();
    model.addAttribute("appointment", appointment);
    model.addAttribute("dateString", "");
    model.addAttribute("cities", cityService.findAll());
    //getAllAgencies(model, city);
    getAllServices(model,agency);
    return "appointment";
}

@RequestMapping(value="/agency", method=RequestMethod.GET)
public String getAllAgencies(Model model, @ModelAttribute("city") City city){
    model.addAttribute("agencies", agencyService.listAllAgencies(city));
    return "redirect:/appointment/create";
}
public void getAllServices(Model model, @ModelAttribute("agency") Agency 
agency){
    if(agency==null){
        return;
    }
    model.addAttribute("services", serService.listAllServices(agency));

}

Answer 1

So I was able solving this using jQuery.

Here is a useful link: http://www.rockhoppertech.com/blog/spring-mvc-3-cascading-selects-using-jquery/ I will post my code below, maybe will help someone

-mycontroller

@RequestMapping(value="/create", method=RequestMethod.GET)
public String createAppointmentPost(Model model, @ModelAttribute("city") City 
city, 
        @ModelAttribute("agency") Agency agency){

    Appointment appointment=new Appointment();
    model.addAttribute("appointment", appointment);
    model.addAttribute("dateString", "");
    model.addAttribute("cities", cityService.findAll());
    return "appointment";
}       

@RequestMapping(value = "/agencies", method = RequestMethod.GET)
public @ResponseBody
List<Agency> findAllAgencies(
        @RequestParam(value = "cityId", required = true) Long cityId) {
    City city = cityService.findCity(cityId);
    return agencyService.listAllAgencies(city);
}

-thymeleaf

<div class="form-group">
    <label for="location">Alege orasul:</label>
    <select  class="form-control" required="required" 
       th:value="${appointment.location}" name="location" id="location">
      <option disabled="disabled" selected="selected" > -- 
      alege orasul --
      </option>
      <option th:each="city : ${cities}" th:value="${city.id}" 
       th:text="${city.name}" >
      </option>
    </select>
</div>

<div class="form-group">
         <label for="location">Alege agentia:</label>
                <select class="form-control" th:value="${appointment.agency}" 
                name="agency" id="agency" required="required">
                    <option disabled="disabled" selected="selected" > --alege 
                    agentia --</option>
                </select>
</div>

jQuery- for one dropdown

 $('#location').change(
        function() {
            $.getJSON("http://localhost:8181/appointment/agencies", {
                cityId : $(this).val(),
                ajax : 'true'
            }, function(data) {
                var html = '<option value="">--alege agentia--</option>';
                var len = data.length;
                for ( var i = 0; i < len; i++) {
                    html += '<option value="' + data[i].nume + '">'
                            + data[i].nume + '</option>';
                }
                html += '</option>';
                $('#agency').html(html);
            });
        });