form:error not showing error - spring

Question

When validating object controller just refreshes the page, instead showing errors via form:errors, can you tell me where is the problem. I guest it needs to get error from binding result and insert it into the page, instead controller is just refreshing page
Controller :
#PreAuthorize("hasRole('ROLE_ADMIN')")
#RequestMapping(value = "/create", method = RequestMethod.POST)
public String createProduct(MultipartFile image, Model model,#ModelAttribute #Valid ProductDto product, BindingResult bindingResult) throws IOException {
productValidator.validate(product,bindingResult);
if (bindingResult.hasErrors()){
return "admin/create";
} else {
return "index";
}
}
#PreAuthorize("hasRole('ROLE_ADMIN')")
#RequestMapping(value = "/create", method = RequestMethod.GET)
public String createProduct(Model model) {
model.addAttribute("product", new ProductDto());
model.addAttribute("categories", categoryService.findAll());
return "admin/create";
}
Validator :
#Override
public boolean supports(Class<?> aClass) {
return ProductDto.class.equals(aClass);
}
#Override
public void validate(Object o, Errors errors) {
ProductDto product = (ProductDto) o;
if (product.getTitle().isEmpty() || product.getTitle() == null) {
errors.rejectValue("title", "product.title", "Product title cant be empty");
}
if (product.getDescription().isEmpty() || product.getDescription() == null) {
errors.rejectValue("description", "product.description", "Product description cant be empty");
}
if (product.getPrice() == null || product.getPrice()<=0) {
errors.rejectValue("price", "product.price", "Product price is not valid");
}
if (product.getCategoryId()==null) {
errors.rejectValue("category", "product.category", "Product category is not valid");
}
}
jstl page :
<spring:url value="/product/create" var="formUrl"/>
<form:form modelAttribute="product" action="${formUrl }" method="post" enctype="multipart/form-data">
<div class="form-group">
<label>Title</label>
<form:input id="title"
cssClass="form-control" path="title"/>
<form:errors path="title"/>
</div>
<div class="form-group">
<label>Description</label>
<form:textarea id="description" rows="10"
cssClass="form-control" path="description"/>
</div>
<div class="form-group">
<label>Price</label>
<form:input id="price" type="number"
cssClass="form-control" path="price"/>
<form:errors path="description"/>
</div>
<div class="form-group">
<label for="sel1">Select category</label>
<form:select id="sel1" cssClass="form-control" path="categoryId">
<form:options items="${categories}" itemValue="id" itemLabel="title"/>
</form:select>
</div>
<label class="btn btn-default btn-file">
Image <input type="file" multiple accept='image/*' ng-file-select="onFileSelect($files)" name="image" style="display: block;">
</label>
<br><br>
<div class="text-center">
<button type="submit" class="btn btn-lg btn-success text-center"><span
class="fa fa-check"></span> Submit
</button>
<a href="/" class="btn btn-danger btn-lg text-center"><span
class="fa fa-times"></span> Cancel
</a>
</div>
</form:form>

Answer 1

I think your product model attribute has different name in your POST-handling method.
According to documentation:
The default model attribute name is inferred from the declared
attribute type (i.e. the method parameter type or method return type),
based on the non-qualified class name: e.g. "orderAddress" for class
"mypackage.OrderAddress", or "orderAddressList" for
"List<mypackage.OrderAddress>".
So your ProductDto product attribute will have name productDto in resulting model. But you referring the product in your template.
Try to explicitly set the name attribute of #ModelAttribute annotation
public String createProduct(MultipartFile image, Model model, #ModelAttribute(name = "product") #Valid ProductDto product, BindingResult bindingResult)
And to make sure that bidning and validation actually works, try to log it:
if (bindingResult.hasErrors()) {
System.err.println("Form has errors!");
}