Catch exception in Ktor-locations if non valid route parameter - kotlin

Question

I'm new in kotlin world. So I have some problem. I'm using ktor framework and try to use ktor-locations (https://ktor.io/servers/features/locations.html#route-classes)
And as example
#Location("/show/{id}")
data class Show(val id: Int)
routing {
get<Show> { show ->
call.respondText(show.id)
}
}
Everything is good, when I try to get /show/1
But if route will be /show/test there is NumberFormatException, cause DefaultConversionService try to convert id to Int and can't do it.
So my question is, how can I catch this exception and return Json with some error data. For example, if not using locations I can do smt like this
routing {
get("/{id}") {
val id = call.parameters["id"]!!.toIntOrNull()
call.respond(when (id) {
null -> JsonResponse.failure(HttpStatusCode.BadRequest.value, "wrong id parameter")
else -> JsonResponse.success(id)
})
}
}
Thx for help!

Answer 1

You can do a simple try-catch in order to catch the parsing exception which is thrown when a string can not be converted to an integer.
routing {
get("/{id}") {
val id = try {
call.parameters["id"]?.toInt()
} catch (e : NumberFormatException) {
null
}
call.respond(when (id) {
null -> HttpStatusCode.BadRequest
else -> "The value of the id is $id"
})
}
}
Other way of handling exception is to use StatusPages module:
install(StatusPages) {
// catch NumberFormatException and send back HTTP code 400
exception<NumberFormatException> { cause ->
call.respond(HttpStatusCode.BadRequest)
}
}
This should work with using Location feature. Please note that Location is experimental above ktor version 1.0.