ModelAttribute adds only 1st value into List

Question

On my view, I generate input "username", select with attribute multiple=multiple, which has name "rolesss".

My issue is, that if I send such form via post, my controller should convert roles to list, but i get only list containing single element.

For example: I send post, with values:

username:MyUser
_csrf:aef50238-92cf-48df-86a4-cb6e2b8f62c9
rolesss:USER
rolesss:ADMIN

In debug mode in my controller I see values: roless: "USER" username: "MyUser"

"ADMIN" did just disappear.

My controller looks like:

@Controller
@RequestMapping("/user-management")
public class UserManagementController {

    @RequestMapping("")
    public ModelAndView home() {
        ModelAndView modelAndView = new ModelAndView();
        modelAndView.setViewName("pages/user-management");

        return modelAndView;
    }

    @RequestMapping(value = "", method = RequestMethod.POST)
    public ModelAndView changeRoles(@ModelAttribute("username") String username,@ModelAttribute("rolesss") List<String> rolesss) {

        return null;
    }

}

My view I merged 2 thymeleaf fragments into 1, in my code #user-roles-form is in separate fragment, but I think that it should not change anything:

<th:block layout:fragment="main-content">
    <section>
        <h2 class="section-title no-margin-top">Role Management</h2>
        <div class="form-group">
            <div class="panel panel-primary">
                <div class="panel-heading">Změna rolí uživatele</div>
                <div class="panel-body">
                    <form class="form-horizontal" role="form" action="/user-management" method="post">
                        <div class="form-group">
                            <label for="user-name" class="col-sm-2 control-label">Uživatel</label>
                            <div class="col-sm-10">
                                <input id="user-name" class="autocomplete form-control" type="text"
                                       placeholder="Jméno uživatele" name="username"/>
                            </div>
                            <input type="hidden"
                                   th:name="${_csrf.parameterName}"
                                   th:value="${_csrf.token}"/>
                        </div>
                        <div id="user-roles-form" th:fragment="roles(roles)" xmlns:th="http://www.thymeleaf.org">
                            <div class="form-group">
                                <label for="user-roles" class="col-sm-2 control-label">Uživatelovy role</label>
                                <div class="col-sm-10">
                                    <select multiple="multiple" class="form-control" id="user-roles" name="rolesss">
                                        <th:block th:each="role : ${roles}">
                                            <option th:value="${role.userRole.role}" th:text="${role.userRole.role}" th:selected="${role.selected}"></option>
                                        </th:block>
                                    </select>
                                </div>
                            </div>
                            <div class="form-group">
                                <div class="col-sm-offset-2 col-sm-10">
                                    <button type="submit" class="btn btn-ar btn-primary">Uložit</button>
                                </div>
                            </div>
                        </div>
                    </form>
                </div>
            </div>
        </div>
    </section>
</th:block>

Answer 1

try using like below in your controller

in your HTML or JSP

 <form modelAttribute="your_model_name"></form>

if you are using model attribute then use @ModelAttribute

otherwise, use @RequestParam("username")

In your case

@RequestMapping(value = "", method = RequestMethod.POST)
public ModelAndView changeRoles(@RequestParam("username") String username,@RequestParam("rolesss") List<String> rolesss) {
     ..........
     .........
    return null;
}