Spring Boot ModelAndView - cannot update value to Model - spring

Question

I am trying to create a form with 3 fields within the class LoginForm: usuario, senha, msgLogin.
I receive the fields usuário and senha from the input boxes and then I try to redirect to the same page with the same fields plus the field MsgLogin. But I've not been able to update the msgLogin field and I don't understand why.
These are the code:
HTML:
<form id="frmLogin" class="form col-md-12" action="#" th:action="#{/login}" th:object="${loginForm}" method="post">
<div class="form-group">
<label for="usuario" class="col-md-1">Usuário: </label>
<input type="text" id="usuario" placeholder="Email" th:field="*{usuario}"/>
</div>
<div class="form-group">
<label for="senha" class="col-md-1">Senha: </label>
<input type="password" id="senha" placeholder="senha" th:field="*{senha}"/>
</div>
<div class="row">
<button id="entrar">Entrar</button>
</div>
<div class="row">
<div id="msgLogin"></div>
<p th:text="${loginForm.msgLogin}" />
</div>
</form>
The Controller:
#RequestMapping("/")
public String init(#ModelAttribute LoginForm loginForm) {
Logger.getAnonymousLogger().info("Tela Inicial.");
return "home";
}
#PostMapping("/login")
public ModelAndView entrar(LoginForm loginForm) throws IOException {
Logger.getAnonymousLogger().info("Entrando no Internet Banking.");
service.login(usuario, senha);
ModelMap model = new ModelMap();
loginForm.setMsgLogin("I want to update that value!");
model.addAttribute("loginForm", loginForm);
return new ModelAndView("redirect:/", model);
}
Class using Lombok:
#Getter
#Setter
public class LoginForm {
private String usuario;
private String senha;
private String msgLogin;
}

Answer 1

A redirect send a 302 HTTP status back to the browser to resubmit using a new url, so it resubmits the same two fields to the new url. There's no expectation of payload data in the 302 response.

Answer 2

In your Controller, change the last line in your entrar method to: return new ModelAndView("/login", model);