如何在Spring Boot登录页面中显示登录失败的错误提示？

Got it, let's get this sorted with the most straightforward approach—since you're working with individual @RequestParam parameters instead of a form-backed entity (which is where BindingResult shines), we can use Spring's Model to pass the error message directly to your login page.

Step 1: Update Your Controller to Send Error Message #

Modify your checkLogin method to accept a Model parameter, and add an error attribute when login fails:

@RequestMapping(value = "/loginCheck", method = RequestMethod.POST)
public String checkLogin(@RequestParam String roll, @RequestParam String pass, Model model) {
    if (studentService.existsByRollAndPass(roll, pass)) {
        return "Welcome";
    } else {
        // Add error message to the model
        model.addAttribute("loginError", "Invalid roll number or password. Please try again.");
        return "Login";
    }
}

Step 2: Modify Your HTML to Display the Error #

Assuming you're using Thymeleaf (Spring Boot's default templating engine), add a section in your login page to show the error message only when it exists. Place this somewhere above your form (or inside it, wherever makes sense for your UI):

<!-- Error message display -->
<div th:if="${loginError != null}" class="alert alert-danger col-md-8 col-md-offset-2">
    <span th:text="${loginError}"></span>
</div>

<form class="form-horizontal" method="post" action="/loginCheck">
    <!-- Your existing form fields here -->
</form>

If you're using JSP instead of Thymeleaf, replace the Thymeleaf code with JSTL:

<c:if test="${not empty loginError}">
    <div class="alert alert-danger col-md-8 col-md-offset-2">
        ${loginError}
    </div>
</c:if>

Why This Works #

Unlike BindingResult (which is for validating form objects annotated with @Valid), this approach directly passes a simple message to the view using Spring's Model—perfect for quick, one-off error cases like login failure. The view then checks if the error attribute exists and renders it only when needed.

内容的提问来源于stack exchange，提问作者Avijit Barua