Spring Boot and Kotlin - How to validate a JSON object - spring

Question

I'm using Spring Boot in Kotlin.
I'm taking in some JSON string, parsing it with ObjectMapper however I want to validate it has everything as in per the model - namely id and s3FilePath are not blank or missing.
So this is the model I want to validate against:
#JsonIgnoreProperties(ignoreUnknown = true)
class MyModel {
var id : String = ""
var s3FilePath : String = ""
}
This is where I use that model:
class FirstMessage {
fun create(newMessage: String) : String {
val objectMapper = ObjectMapper()
val parsedMap : MyModel = objectMapper.readValue(newMessage, MyModel::class.java)
val result = MyModel()
result.id = parsedMap.id
result.s3FilePath = parsedMap.s3FilePath
return objectMapper.writeValueAsString(result)
}
}
And finally I have this test where I want to validate an exception:
#Test
fun incompleteDataReturnsException() {
var input = """{"missing": "parts"}"""
// FirstMessage().create(input) // Will make some assertion here here
}
Any help would be appreciated. I've just started using Spring and its pretty 'intense'.
Thanks.
p.s. If creating that model wrong/there's a better way, please let me know. I'm a little unsure if thats the correct way.

Answer 1

You should use data classes for the models. Also, use kotlin jacksonObjectMapper() instead of ObjectMapper(). Standard ObjectMapper will not work in Kotlin. Or inject ObjectMapper from Spring context. Add "com.fasterxml.jackson.module:jackson-module-kotlin" in your dependencies.
#JsonIgnoreProperties(ignoreUnknown = true)
data class MyModel (
val id : String,
val s3FilePath : String
)
import com.fasterxml.jackson.module.kotlin.jacksonObjectMapper
import com.fasterxml.jackson.module.kotlin.readValue
class FirstMessage {
fun create(newMessage: String) : String {
val parsedMap : MyModel = jacksonObjectMapper().readValue(newMessage)
return jacksonObjectMapper().writeValueAsString(parsedMap)
}
}
class FirstMessageTest {
#Test
fun incompleteDataReturnsException() {
val input = """{"missing": "parts"}"""
assertThrows (MissingKotlinParameterException::class.java
{FirstMessage().create(input)} // Will make some assertion here here
}
#Test
fun `Should parse`() {
val input = """{"id":"id",
"missing": "parts",
"s3FilePath":"somePath"}"""
FirstMessage().create(input) // Will make some assertion here here
}
}

Answer 2

If I understood your question correct, you just want to check if your required properties are set. So I would suggest checking for that properties after you parsed the string with something like this:
class FirstMessage {
fun create(newMessage: String) : String {
val objectMapper = ObjectMapper()
// validation 1: your input is valid JSON
val parsedMap : MyModel = objectMapper.readValue(newMessage, MyModel::class.java)
// validation 2: check that your properties are set
if(parsedMap.id.isNullOrEmpty() ||
parsedMap.s3FilePath.isNullOrEmpty())
{
throw IllegalArgumentException("Invalid input")
}
val result = MyModel()
result.id = parsedMap.id
result.s3FilePath = parsedMap.s3FilePath
return objectMapper.writeValueAsString(result)
}
}
Depending of the scope, a nicer solution would be a new annotation like #NotEmpty that you set on the properties of your target class that are required and have a generic parser function which validates all the annotated fields on your parsed object and throws a better exception which says exactly which fields are missing.