Spring MVC passing ArrayList back to controller

Question

I am new to Spring. I display a list with users. Every row has a checkbox for removing the users.

Controller:

@Controller
public class AdminController {

    @Autowired
    private UserDao userDao;

    @RequestMapping(value = "/admin", method = RequestMethod.GET)
    public ModelAndView adminPage() {
        ModelAndView model = new ModelAndView();
        model.addObject("users", userDao.findAll());
        model.setViewName("admin");
        return model;

    }

    @RequestMapping(value = "admin/remove", method = RequestMethod.POST)
    public ModelAndView removeUser(@ModelAttribute(value = "users") ArrayList<User> users) {
        ModelAndView model = new ModelAndView();
        //UPDATE USERS HERE 
        model.setViewName("redirect:/admin");
        return model;

    }

JSP:

<form:form action="/admin/remove" method="POST"  modelAttribute="users">
            <table class="table table-striped">
                <thead>
                    <tr>
                        <th>Firstname</th>
                        <th>Lastname</th>
                        <th>Email/login</th>
                        <th>Profession</th>
                        <th>Select<th>
                    </tr>
                </thead>
                <tbody>
                    <c:forEach var="user" items="${users}">
                        <tr>
                            <td>${user.firstName}</td>
                            <td>${user.lastName}</td>
                            <td>${user.login}</td>
                            <td>${user.profession}</td>
                            <td><input type="checkbox" value="${user.delete}"/></td>
                        </tr>
                    </c:forEach>
                </tbody>
            </table>            
            <input type="submit" value="Delete user(s)" class="btn-danger" />
            <input type="hidden" name="${_csrf.parameterName}" value="${_csrf.token}" />
            </form:form>

The list is rendered correctly. If i press the "Delete user(s)" button. The @modelAttribute users is empty. I also tried wrapping the list in a new class, but i get the same results.

Any ideas?

Answer 1

Thanks to minion, i found the answer

Wrapper:

public class UserListWrapper {

private ArrayList<User> users;

public ArrayList<User> getUsers() {
    return users;
}

public void setUsers(ArrayList<User> users) {
    this.users = users;
}

Controller:

@Controller
public class AdminController {

@Autowired
private UserDao userDao;

@RequestMapping(value = "/admin", method = RequestMethod.GET)
public ModelAndView adminPage() {
    ModelAndView model = new ModelAndView();
    UserListWrapper wrapper = new UserListWrapper();
    wrapper.setUsers(new ArrayList<User>(userDao.findAll()));
    model.addObject("userListWrapper",wrapper);

    model.setViewName("admin");
    return model;

}

@RequestMapping(value = "admin/remove", method = RequestMethod.POST)
public ModelAndView removeUser(@ModelAttribute(value = "userListWrapper") UserListWrapper userListWrapper) {
    ModelAndView model = new ModelAndView();
    userDao.removeFlaggedUsers(userListWrapper.getUsers());
    model.setViewName("redirect:/admin");
    return model;

}

}

View:

<form:form action="/admin/remove" method="POST"  modelAttribute="userListWrapper">
        <table class="table table-striped">
            <thead>
                <tr>
                    <th>First name</th>
                    <th>Last name</th>
                    <th>Email/login</th>
                    <th>Profession</th>
                    <th>Select<th>
                </tr>
            </thead>
            <tbody>
                <c:forEach varStatus="us" var="user" items="${userListWrapper.users}" >
                    <tr>
                        <td><form:input type="hidden" path="users[${us.index}].firstName"/>${user.firstName}</td>
                        <td><form:input type="hidden" path="users[${us.index}].lastName"/> ${user.lastName}</td>
                        <td><form:input type="hidden" path="users[${us.index}].login"/>${user.login}</td>
                        <td><form:input type="hidden" path="users[${us.index}].profession"/>${user.profession}</td>
                        <td><form:checkbox path="users[${us.index}].delete" value="${user.delete}"/></td>
         <form:input type="hidden" path="users[${us.index}].id"/>
                    </tr>
                </c:forEach>
            </tbody>
        </table>            
        <input type="submit" value="Delete user(s)" class="btn-danger" />
        <input type="hidden" name="${_csrf.parameterName}" value="${_csrf.token}" />
        </form:form>

Thank you!

EDIT: Dont forget to also add the fields you are not displaying.

For example:

If you dont add the id, your delete will not work because the id in the returned User object will be NULL.

Answer 2

Your ModelAttribute is empty as there is no form data binding happening from your jsp to your model attribute. Take a look at how Spring sample for binding collections " http://developer.ucsd.edu/develop/user-interface/building-a-form/form-binding-with-collections.html ". This will help you to understand.

Most of the Spring application typically uses form:input with " path " parameter to do data binding.

Answer 3

You should build your functionality around spring-mvc select tag. Few changes would be in order though, push a list to a POJO class eg

public class FormBean {

    private List<String> users;

    public FormBean() {

    }

    public List<String> getUsers() {
        return users;
    }

    public void setUsers(List<String> users) {
        this.users = users;
    }
}

change your mapping to

@RequestMapping(value = "admin/remove", method = RequestMethod.POST)
    public ModelAndView removeUser(@ModelAttribute(value = "formBean") FormBean formBean) {

finally, swap your c:forEach with springs select tag, so something like

<form:form action="/admin/remove" method="POST"  modelAttribute="formBean">
  ...
 <form:select path="users" items="${users}" multiple="true" />
  ...
</form>

Answer 4

This is because you are using a redirect: in your view. Have a look on Flash Attributes :

• http://docs.spring.io/spring/docs/current/javadoc-api/org/springframework/web/servlet/mvc/support/RedirectAttributes.html
• http://viralpatel.net/blogs/spring-mvc-flash-attribute-example/

You should be able to get the updated list :)