Passing error message from controller to thymeleaf

Question

I dont know how to pass an error to thymeleaf outside a form and not specific to a field. Just a small check if the book is on stock. If yes, process everything. If not, throw a error message on the client side.

Controller

@PostMapping("/books/borrow/{id}")
    public String borrowBook(@PathVariable int id, Errors errors) {

        Book borrowedBook = bookRepository.findById(id);

        if (borrowedBook.getAvailableCount() == 0){
            errors.rejectValue("onStock", "Book out of stock. Come later...");
            return "redirect:/books/";
        } else{...}

View

<p th:text="${onStock}"></p>

I don't undestand how to pass the parameter and show it to the client. I did research https://www.thymeleaf.org/doc/tutorials/2.1/thymeleafspring.html#validation-and-error-messages but they are all specific to a form and field.

What am i doing wrong?

Answer 1

You can use a RedirectAttribute to achieve that:

Controller

@PostMapping("/books/borrow/{id}")
    public String borrowBook(@PathVariable int id, Errors errors, RedirectAttributes redirectAttributes) {
    Book borrowedBook = bookRepository.findById(id);

    if (borrowedBook.getAvailableCount() == 0){
        errors.rejectValue("onStock", "Book out of stock. Come later...");
        redirectAttributes.addFlashAttribute("errorMessage", "We couldn't process your order!");
        return "redirect:/books/borrow/" + id;
    } else {
        //Process the request
    }

Template (HTML)

<div th:if="${errorMessage}">
    <div th:text="${errorMessage}"></div>
</div>