Cannot convert value of type MultipartFile to String - spring

Question

When I added validation for field Name I got an error:
Validation failed for object='item'. Error count: 1org.springframework.validation.BindException
Field error in object 'item' on field 'image': rejected java.lang.IllegalStateException: Cannot convert value of type 'org.springframework.web.multipart.support.StandardMultipartHttpServletRequest$StandardMultipartFile' to required type 'java.lang.String' for property 'image': no matching editors or conversion strategy found
Entity, class Item
#Entity
#Table(name = "items")
public class Item {
#Id
#GeneratedValue(strategy = GenerationType.AUTO)
#Column(name = "id")
private int id;
#NotBlank(message = "Введите наименование")
#Column(name = "name")
private String name;
#JsonIgnore
#Lob
#Column(name = "image")
private String image;
}
Main controller
#PostMapping("/items")
public String add(
#Valid Item item,
#RequestParam("image") MultipartFile file,
BindingResult bindingResult,
Model model
) throws IOException {
if (bindingResult.hasErrors()){
Map<String, String> errorsMap = ControllerUtils.getErrors(bindingResult);
model.mergeAttributes(errorsMap);
model.addAttribute("item", item);
} else {
if (file != null && !file.getOriginalFilename().isEmpty()) {
byte[] data = file.getBytes();
String imageString = Base64.getEncoder().encodeToString(data);
item.setImage(imageString);
}
model.addAttribute("item", null);
itemService.saveItem(item);
}

Answer 1

I solved the problem by creating new formParams (quite similar with entity Items with all validation parameters) and put this form as a parameter to the post method.
#PostMapping("/items/save")
public String add(#AuthenticationPrincipal User user, #Valid ItemInputParams formParams,
BindingResult bindingResult, Model model) throws IOException {
if (bindingResult.hasErrors()){
Map<String, String> errorsMap =
ControllerUtils.getErrors(bindingResult);
model.mergeAttributes(errorsMap);
model.addAttribute("item", formParams);
return initItems(null, model);
}
Item item = new Item();
item.setName(formParams.getName());
(...)
MultipartFile file = formParams.getImage();
if (file != null && !file.getOriginalFilename().isEmpty()) {
byte[] data = file.getBytes();
String imageString = Base64.getEncoder().encodeToString(data);
item.setImage(imageString);
}
(...)
}

Answer 2

Ensure you have an enctype in your form opening tag and also ensure the name in the request param is the same name in the form and in the database field