绑定结果给出白标签错误页

Question

<div th:if="${parentCategories.size() == 0}">
        <span>There are no categories, please, add some categories!</span>
    </div>
    <div th:unless="${parentCategories.size() == 0}">
        <label for="subcategoryForm">Add a subcategory</label>
        <form id="subcategoryForm" th:action="@{/category/add-subcategory}" th:object="${category}" method="post">

            <label for="name">Category name</label>
            <input id="name" type="text" th:field="*{categoryName}"/>
            <span th:if="${#fields.hasErrors('categoryName')}" th:errors="*{categoryName}" th:errorclass="error"></span>

            <label for="selectParentCategory">Enter a parent category</label>
            <select id="selectParentCategory" th:field="*{parentCategoryName}">
                <option th:each="category : ${parentCategories}"
                        th:value="${category.categoryName}"
                        th:text="${category.categoryName}"/>
                <span th:if="${#fields.hasErrors('parentCategoryName')}" th:errors="*{parentCategoryName}" th:errorclass="error"></span>
            </select>

            <button type="submit">Add category</button>
        </form>
    </div>

@Setter
@Getter
public class CategoryDTO {

    @CategoryValidator
    private String categoryName;

    @ParentCategoryValidator
    private String parentCategoryName;

}

@CategoryValidator由CategoryValidatorImpl验证：

@Autowired
    private CategoryRepository categoryRepository;

    @Override
    public boolean isValid(String value, ConstraintValidatorContext context) {
        if(value.isBlank()){
            context.disableDefaultConstraintViolation();
            context.buildConstraintViolationWithTemplate("{categoryDTO.blank}").addConstraintViolation();
            return false;
        }

        Optional<Category> optionalCategory = categoryRepository.findByName(value);
        if (optionalCategory.isPresent()) {
            context.disableDefaultConstraintViolation();
            context.buildConstraintViolationWithTemplate("{categoryDTO.alreadyExists}").addConstraintViolation();
            return false;
        }

        Pattern pattern = Pattern.compile("[a-zA-Z\\s]*");
        Matcher matcher = pattern.matcher(value);
        if (!matcher.matches()) {
            context.disableDefaultConstraintViolation();
            context.buildConstraintViolationWithTemplate("{categoryDTO.name.invalid}").addConstraintViolation();
            return false;
        }

        return true;
    }

和CategoryController的一部分：

@GetMapping("/subcategory-form")
public String getSubcategoryForm(Model model){
    List<CategoryDTO> listOfParentCategories = categoryService.getParentCategories();
    model.addAttribute("category", new CategoryDTO());
    model.addAttribute("parentCategories", listOfParentCategories);
    return "add-subcategory-form";
}

@PostMapping("/add-subcategory")
public String addSubcategory(@Valid @ModelAttribute("category") CategoryDTO categoryDTO, BindingResult bindingResult){
   

 if(bindingResult.hasErrors()){
            return "add-subcategory-form";
        }
        categoryService.add(categoryDTO);
        return "redirect:/category/subcategory-form";
    }  

在输入字段中，当我输入一个空白时，验证器使用控制器中的hasErrors正确地发现它，但当我在发现空白并返回false后返回表单时，它会给出以下信息：

Answer 1

stacktrace对此问题有以下提示：

计算SpringEL表达式的异常：“parentcategories.size()==0”（模板：“add-subcategories-form”-第13行，col 10）

和：

@PostMapping("/add-subcategory")
public String addSubcategory(@Valid @ModelAttribute("category") CategoryDTO categoryDTO, BindingResult bindingResult) {
   
        if(bindingResult.hasErrors()){
            List<CategoryDTO> listOfParentCategories = categoryService.getParentCategories();
            model.addAttribute("parentCategories", listOfParentCategories);
            return "add-subcategory-form";
        }
        categoryService.add(categoryDTO);
        return "redirect:/category/subcategory-form";
    }