How to validate json in kotlin - kotlin

Question

There is a kotlin class with the following structure.
data class Person(
#field:Length(max = 5)
val name: String,
val phones: List<Phone>
)
data class Phone(
#field:Length(max = 10)
val number: String
)
When converting the json string through objectMapper, I want to receive all the violation values.
ex) JSON object is not valid. Reasons (3) name length must be 5, number length must be 10, ...
#Test
fun test() {
val json = """
{
"name": "name",
"phones": [
{ "number": "1234567890123456" },
{ "number": "1234567890123456" }
]
}
""".trimIndent()
try {
objectMapper.readValue(json, Person::class.java)
} catch (ex: ConstraintViolationException) {
val violations = ex.constraintViolations
println(violations.size) // expected size = 3
}
}
However, the above code fails to catch the exception and causes the exception below.
com.fasterxml.jackson.databind.JsonMappingException: JSON object is not valid. Reasons (1): {"bean":"Phone","property":"number","value":"1234567890123456","message": "..."}, (through reference chain: Person["phones"]->java.util.ArrayList[0])
Looking at the reason, those wrapped in a list do not throw ConstructionViolationException, but throw JsonMappingException.
below dependencies
plugins {
id("org.springframework.boot") version "2.4.3"
id("io.spring.dependency-management") version "1.0.11.RELEASE"
kotlin("jvm") version "1.4.30"
kotlin("plugin.spring") version "1.4.30"
}
dependencies {
implementation("org.springframework.boot:spring-boot-starter-web")
implementation("org.springframework.boot:spring-boot-starter-validation")
testImplementation("org.springframework.boot:spring-boot-starter-test")
}
class BeanValidationDeserializer(base: BeanDeserializerBase?) : BeanDeserializer(base) {
private val logger = LoggerFactory.getLogger(this::class.java)
private val validator = Validation.buildDefaultValidatorFactory().validator
override fun deserialize(parser: JsonParser?, ctxt: DeserializationContext?): Any {
val instance = super.deserialize(parser, ctxt)
validate(instance)
return instance
}
private fun validate(instance: Any) {
val violations = validator.validate(instance)
if (violations.isNotEmpty()) {
val message = StringBuilder()
message.append("JSON object is not valid. Reasons (").append(violations.size).append("): ")
for (violation in violations) {
message.append("{\"bean\":\"${violation.rootBeanClass.name}\",")
.append("\"property\":\"${violation.propertyPath}\",")
.append("\"value\":\"${violation.invalidValue}\",")
.append("\"message\": \"${violation.message}\"}")
.append(", ")
}
logger.warn(message.toString())
throw ConstraintViolationException(message.toString(), violations)
}
}
}
#Bean
fun objectMapper(): ObjectMapper = Jackson2ObjectMapperBuilder.json()
.featuresToDisable(MapperFeature.DEFAULT_VIEW_INCLUSION)
.featuresToDisable(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES)
.featuresToDisable(SerializationFeature.WRITE_DATES_AS_TIMESTAMPS)
.modules(ParameterNamesModule(), JavaTimeModule(), Jdk8Module(), KotlinModule(), customValidationModule())
.build()
#Bean
fun customValidationModule(): SimpleModule {
val validationModule = SimpleModule()
validationModule.setDeserializerModifier(object : BeanDeserializerModifier() {
override fun modifyDeserializer(
config: DeserializationConfig?,
beanDesc: BeanDescription?,
deserializer: JsonDeserializer<*>?
): JsonDeserializer<*>? {
return if (deserializer is BeanDeserializer) {
BeanValidationDeserializer(deserializer as BeanDeserializer?)
} else deserializer
}
})
return validationModule
}
I'm not sure how to do it. I ask for your help.

Answer 1

I would say an easier and more maintainable way would be to define a JSON Schema.
After that is in place, you can use one of the two json validation libraries mentioned here (https://json-schema.org/implementations.html#validator-kotlin) to validate your json.

Answer 2

The answer by #rbs is good but requires the overhead of creating json schema per json you want to validate.
Seems like object mapper can be configured not to wrap the exceptions it throws with JsonMappingException. - https://github.com/FasterXML/jackson-databind/issues/2033
All you need to do is to disable WRAP_EXCEPTIONS feature for the objectmapper
Note you cant choose a specific exception type, it will not wrap ALL the exceptions.