How to show error message in login page when user fail to login with Spring Boot?

Question

Now i am doing project with Spring Boot. I wanted to show error message when I fail to login. When I did Maven project I did it easily with BindingResult. I followed several instruction to complete the task what I wanted to do. But I couldn't get any proper solution. I need a proper solution in simplest way.

Here my Controller class

  @RequestMapping(value = "/loginCheck", method = RequestMethod.POST)
    public String checkLogin(@RequestParam String roll, @RequestParam String pass) {
        if (studentService.existsByRollAndPass(roll, pass)) {
            return "Welcome";
        } else {
            return "Login";
        }

And my html file is

  <form class="form-horizontal" method="post" action="/loginCheck">

        <fieldset>


            <div class="form-group">
                <label class="col-md-4 control-label" for="textinput">Roll</label>
                <div class="col-md-4">
                    <input id="textInput" name="roll" type="text"
                           placeholder="Roll" class="form-control input-md">

                </div>
            </div>
            <!-- Password input-->
            <div class="form-group">
                <label class="col-md-4 control-label" for="password">Password</label>
                <div class="col-md-4">
                    <input id="password" name="pass" type="password"
                           placeholder="password" class="form-control input-md">

                </div>
            </div>
            <!-- Button -->
            <div class="form-group">
                <label class="col-md-4 control-label" for="login"></label>
                <div class="col-md-4">
                    <button id="login" name="login" class="btn btn-primary">Login</button>
                </div>
            </div>

        </fieldset>

    </form>

Answer 1

您可以在 URL 中添加一个错误参数，例如 localhost:8080/login?error。然后，在 Thymeleaf 的帮助下，您可以将这个 div 添加到 html 中。

<div th:if="${param.error}" class="alert alert-danger">    
    Invalid username and password.
</div>

如果 URL 中存在错误参数，则会显示此 div。

但是，您可能需要更改

return "Login"

到

return "redirect:Login?error";