MethodArgumentNotValidException not thrown in case of validation fail - spring

Question

I'm trying to implement validation in Spring REST by following this tutorial. Though, my code is in Koltin unlike the tutorial.
My code is as follows -
Entity class
#Entity
class PodcastEntity(#Id #GeneratedValue(strategy = GenerationType.AUTO) #NotNull
var id: Long = 0,
#field:NotEmpty(message = "Please provide an author")
var author: String,
#field:NotEmpty(message = "Please provide a title")
var title: String,
#field:NotEmpty(message = "Please provide a description")
var description: String,
#field:NotEmpty(message = "Please provide category one")
var categoryOne: String,
#field:NotEmpty(message = "Please provide category two")
var categoryTwo: String,
var filePath: String = "")
My post method is like this in the controller -
#PostMapping("details")
fun addPodcast(#Valid #RequestBody podcastEntity: PodcastEntity) {
podcastService.addPodcast(podcastEntity)
}
My POST request in postman is like this -
{
"author" : "me 3",
"title" : "File three",
"description" : "this is a test desc"
}
Since categoryOne and categoryTwo are missing and I have not handled the exception on my own, my console should show MethodArgumentNotValidException according to the tutorial. However, I'm getting no such exception. What I'm getting is a HttpMessageNotReadableException exception -
Resolved [org.springframework.http.converter.HttpMessageNotReadableException: JSON parse error: Instantiation of [simple type, class com.krtkush.test.entities.PodcastEntity] value failed for JSON property categoryOne due to missing (therefore NULL) value for creator parameter categoryOne which is a non-nullable type; nested exception is com.fasterxml.jackson.module.kotlin.MissingKotlinParameterException: Instantiation of [simple type, class com.krtkush.test.entities.PodcastEntity] value failed for JSON property categoryOne due to missing (therefore NULL) value for creator parameter categoryOne which is a non-nullable type at [Source: (PushbackInputStream); line: 5, column: 1] (through reference chain: com.krtkush.test.entities.PodcastEntity["categoryOne"])]
I'm unable to understand where I'm going wrong. Some help please?

Answer 1

You can handle this issue by providing HttpMessageNotReadableException handler
and then checking if the main cause is MissingKotlinParameterException.
After that, you can provide custom validation error.
#ExceptionHandler
override fun handleMessageNotReadableException(
exception: HttpMessageNotReadableException,
request: NativeWebRequest
): ResponseEntity<Problem> {
// workaround
val cause = exception.cause
if (cause is MissingKotlinParameterException) {
val violations = setOf(createMissingKotlinParameterViolation(cause))
return newConstraintViolationProblem(exception, violations, request)
}
return create(Status.BAD_REQUEST, UnableToReadInputMessageProblem(), request)
}
private fun createMissingKotlinParameterViolation(cause: MissingKotlinParameterException): Violation {
val name = cause.path.fold("") { jsonPath, ref ->
val suffix = when {
ref.index > -1 -> "[${ref.index}]"
else -> ".${ref.fieldName}"
}
(jsonPath + suffix).removePrefix(".")
}
return Violation(name, "must not be null")
}
This way you get get nice output with proper constraint error.
You may try to declare #ExceptionHandler for MissingKotlinParameterException directly.
Answer based on question Spring not null validation throwing HttpMessageNotReadableException instead of MethodArgumentNotValidException in kotlin

Answer 2

Following Damian's SO link in his answer, I found the first answer really helpful and more appropriate. I modified the #Entitiy class by making the required fields nullable (?) like this -
#Entity
class PodcastEntity(#Id #GeneratedValue(strategy = GenerationType.AUTO)
var id: Long = 0,
#field:NotEmpty(message = "Please provide an author")
var author: String?,
#field:NotEmpty(message = "Please provide a title")
var title: String?,
#field:NotEmpty(message = "Please provide a description")
var description: String?,
#field:NotEmpty(message = "Please provide category one")
var categoryOne: String?,
#field:NotEmpty(message = "Please provide category two")
var categoryTwo: String?,
var filePath: String = "")
This makes sure that the code throws MethodArgumentNotValidException in all three cases - 1. Empty argument 2. null argument 3. Missing argument