Why @Valid annotation not working when used inside service method argument but works for controller

[Puspender Tanwar]

I am having this UserDto class which I want to put under @Valid

@Getter @Setter
public class UserDto{

  @NotEmpty(message = "Name cannot be empty")
  private String name;

  @NotNull(message = "Provide a valid age")
  private Integer age;

}

I have some requirements where I can't put validation on controller method, but I need to do it on the service method.

@PostMapping(value = "/user")
public void create(@RequestBody UserDto user){
  userService.create(user);
}

public void create(@Valid UserDto user){
  System.out.println(user);
}

But this is not working. And if I put @Valid on the controller method, I do get the validation errors as expected.
Why so? Does serialization/deserialization has something to do with valition?

[Salil Wadnerkar]

@Valid is processed by Spring MVC for MVC controllers, not for any other classes.
This is so that it can return a bad request (400) error on these validation failures automatically.

[Puspender Tanwar]

Salil Wadnerkar wrote:@Valid is processed by Spring MVC for MVC controllers, not for any other classes.
This is so that it can return a bad request (400) error on these validation failures automatically.

What solution do we have then? I want to validate the object in exactly same manner as Spring does. Does spring provide any support for that?

[Salil Wadnerkar]

You can use Spring AOP for your non-Spring MVC related beans: https://www.baeldung.com/javax-validation-method-constraints

[Claude Moore]

In Spring Boot  you could annotate with @Validated your @Service class to get all @Valid annotated params in methods to be validated.

[Puspender Tanwar]

Claude Moore wrote:In Spring Boot  you could annotate with @Validated your @Service class to get all @Valid annotated params in methods to be validated.

That changes the returned response. The "object" and "field" returned in the JSON are different with @Validated. The "object" now contains "myUserService" and the "field" conatins "myUserService.nethod.name"

[Puspender Tanwar]

Problem solved using javax.validation.Validator.validate(object) which gives the failed constraints.

[Claude Moore]

Glad you solved, anyway sounds strange that using @Validated on a Service will cause the returning json to be modified.
Could you post some code excerpt ?

[Claude Moore]

Ok, done some tests: please consider following code:

@RestController
@RequestMapping("/user")
public class MyRestController {

	@Autowired
	CheckUser service;
	
	
	@PostMapping(consumes = "application/json", produces = "application/json", path = "/login")
	public UserDTO checkUser(@RequestBody @Valid UserDTO userLogin) throws Exception {
		try {
			return userLogin;
		}
		catch(Exception ex) {
			return userLogin; // never thrown
		}
	}
	
	@PostMapping(consumes = "application/json", produces = "application/json", path = "/loginservice")
	public UserDTO checkUserViaService(@RequestBody  UserDTO userLogin) throws Exception {
		try {
			return service.checkUser(userLogin);
		}
		catch(Exception e) {
			return userLogin; //  thrown when validation error occurs.
		}
	}
}


@Service
@Validated
public class CheckUser {
	
	public UserDTO checkUser(@Valid UserDTO dto) throws Exception {
		return dto;
	}
}

What makes the difference is that the first method is handled directly by Spring, which return a quite complex response with a full trace of the validation error. Using a service, when validation isn't satisfied an exception is thrown, which is in turn returned to the caller as a much simpler JSON response.
So, which approach is best ? I'd vote for putting the validation logic in a @Service, if present: this way, one could catch the exception and handle it the way he prefers.