How to apply request body validation with error details?

[maiden haven]

Hello there,
I want to apply request body validation to my Spring project

import jakarta.validation.constraints.*;

data class RequestBodyDTO(
    @NotBlank(message = "ID is required.")
    val iD: String
)

and this endpoint

import jakarta.validation.Valid
import org.springframework.http.ResponseEntity
import org.springframework.web.bind.annotation.*

@RestController()
@RequestMapping("/foo")
class Handler {
    @PostMapping
    fun handle(@Valid @RequestBody requestBody: RequestBodyDTO): ResponseEntity<Unit> {
        return ResponseEntity.ok().build()
    }
}

I thought @Valid would handle it for me but actually the API consumer still gets a 400 without any error details. So the consumer doesn't know what's wrong.

After googling around I think Spring doesn't do that for me out of the box. So I created an additional class

import org.springframework.http.HttpStatus
import org.springframework.validation.FieldError
import org.springframework.web.bind.MethodArgumentNotValidException
import org.springframework.web.bind.annotation.*

@ControllerAdvice
class ValidationExceptionHandler {
    @ResponseStatus(HttpStatus.BAD_REQUEST)
    @ExceptionHandler(MethodArgumentNotValidException::class)
    fun handleValidationException(
        exception: MethodArgumentNotValidException
    ): Map<String, String?> {
        return exception.bindingResult.allErrors.associate { error ->
            val fieldName = (error as FieldError).field
            val errorMessage = error.defaultMessage

            fieldName to errorMessage
        }
    }
}

Unfortunately the result is the same, the API consumer won't get any error details. Is something missing? Do I even need the ValidationExceptionHandler ? How do I achieve this?

Thanks! 🙂

[honest creek]

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[dapper geyser]

you can create a class that sums up all the validation errors and return it to the consumer

so you get something like
"error_message": "ID is required."

which is basically something that ur trying to do

also try using @RestControllerAdvice

[maiden haven]

would you mind telling me how to do this? ValidationExceptionHandler is wrong?

[dapper geyser]

https://www.bezkoder.com/spring-boot-restcontrolleradvice/
you can check here how they do it

and no its not wrong

 @ExceptionHandler(value = {ResourceNotFoundException.class, CertainException.class})
  @ResponseStatus(value = HttpStatus.NOT_FOUND)
  public ErrorMessage resourceNotFoundException(ResourceNotFoundException ex, WebRequest request) {
    ErrorMessage message = new ErrorMessage(
        status,
        date,
        ex.getMessage(),
        description);
    
    return message;
  }

from that site

and that class error message will be returned to the client

but yea first swap to rest controller advice

[maiden haven]

@dapper geyser thank you. I tried to follow the blog post and just changed from @ControllerAdvice to @RestControllerAdvice since ErrorMessage is just a custom type, I want to make use of problem details later on

Still, doesn't work 😦

[honest creek]

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[dapper geyser]

yes you need to create a custom class

and it will return that class when an error happens

[maiden haven]

you mean like so?

import org.springframework.http.HttpStatus
import org.springframework.validation.FieldError
import org.springframework.web.bind.MethodArgumentNotValidException
import org.springframework.web.bind.annotation.ExceptionHandler
import org.springframework.web.bind.annotation.ResponseStatus
import org.springframework.web.bind.annotation.RestControllerAdvice

@RestControllerAdvice
class ValidationExceptionHandler {
    @ResponseStatus(HttpStatus.BAD_REQUEST)
    @ExceptionHandler(MethodArgumentNotValidException::class)
    fun handleValidationException(
        exception: MethodArgumentNotValidException
    ): ValidationErrorResponse {
        val fieldErrors = exception.bindingResult.allErrors.associate { error ->
            val fieldName = (error as FieldError).field
            val errorMessage = error.defaultMessage

            fieldName to errorMessage
        }

        return ValidationErrorResponse(fieldErrors)
    }
}

data class ValidationErrorResponse(val fieldErrors: Map<String, String?>)

That still doesn't work 😦

[dapper geyser]

so what happens

when the id is invalid

[maiden haven]

nothing, when I set a breakpoint, it won't run the function

[dapper geyser]

but what happens when the id is invalid

does it return the full stacktrace

[maiden haven]

you only get a 400 with

{
    "timestamp": "2025-01-12T18:11:01.102+00:00",
    "path": "/foo",
    "status": 400,
    "error": "Bad Request",
    "requestId": "2e927c69-2"
}

[dapper geyser]

and you want the

"ID is required"

right

[maiden haven]

yes please

[dapper geyser]

exception.getFieldErrors().forEach(fieldError ->
                validationError.addViolation(fieldError.getField(), fieldError.getDefaultMessage()));

you can do something like this

basically

in that method argument not valid exception

you run the get field errors

and just add it to a lsit

[maiden haven]

sorry, the function handleValidationException never runs

if /foo is valid, it executes the rest handler, if it's invalid then Spring responds with a 400, so handleValidationException never runs

[dapper geyser]

but it returns this

change the response status to maybe

not found

[maiden haven]

yes, the default Spring behavior for invalid request bodies I guess

[dapper geyser]

and see if that changes anything

 @ResponseStatus(HttpStatus.NOT_FOUND)

set to this

and see if it changes the error code

should be 404 instead of 400

[maiden haven]

no, same for INTERNAL_SERVER_ERROR

Is there some Spring magic required? Do I have to place this exception handler file into a specific directory with a conventional name or so...

[dapper geyser]

hmmmmmmmm

@RestControllerAdvice
public class CustomExceptionHandler {
    @ExceptionHandler({yourerrorhere.class})
    @ResponseStatus(HttpStatus.NOT_FOUND)
    public ErrorHandler handleNotFoundExceptions(RuntimeException exception) {
        return new ErrorHandler(exception.getMessage());
    }

@Getter
@RequiredArgsConstructor
public class ErrorHandler {
    private final String message;
}

can you try doing something like this

errorhandler is a separate class

also make sure you are using the correct notblank annotation

from jakarta.validation.constraints

[maiden haven]

yes, I think I got this ( as shown in my code above )

[dapper geyser]

ok so try with the example i sent