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•Created by Garzec on 1/12/2025 in #java-help

How to apply request body validation with error details?

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
)

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()
    }
}

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
        }
    }
}

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! 🙂

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