DataConversion is a feature that allows to serialize and deserialize a list of values.
By default, it handles primitive types and enums, but it can also be configured to handle additional types.
If you are using the Locations feature and want to support custom types as part of its parameters, you can add new custom converters with this service.
Table of contents:
io.ktor.features.DataConversion 类中定义，无需任何额外构件。
Installing the DataConversion is pretty easy, and it should be cover primitive types:
install(DataConversion)
The DataConversion configuration, provide a convert<T> method to define
type conversions. Inside, you have to provide a decoder and an encoder
with the decode and encode methods accepting callbacks.
converter: (values: List<String>, type: Type) -> Any?
Accepts values, a list of strings) representing repeated values in the URL, for example, a=1&a=2,
and accepts the type to convert to. It should return the decoded value.converter: (value: Any?) -> List<String>
Accepts an arbitrary value, and should return a list of strings representing the value.
When returning a list of a single element, it will be serialized as key=item1. For multiple values,
it will be serialized in the query string as: samekey=item1&samekey=item2.For example:
install(DataConversion) {
convert<Date> { // this: DelegatingConversionService
val format = SimpleDateFormat.getInstance()
decode { values, _ -> // converter: (values: List<String>, type: Type) -> Any?
values.singleOrNull()?.let { format.parse(it) }
}
encode { value -> // converter: (value: Any?) -> List<String>
when (value) {
null -> listOf()
is Date -> listOf(SimpleDateFormat.getInstance().format(value))
else -> throw DataConversionException("Cannot convert $value as Date")
}
}
}
}
Another potential use is to customize how a specific enum is serialized. By default enums are serialized and de-serialized
using its .name in a case-sensitive fashion. But you can for example serialize them as lower case and deserialize
them in a case-insensitive fashion:
enum class LocationEnum {
A, B, C
}
@Location("/") class LocationWithEnum(val e: LocationEnum)
@Test fun `location class with custom enum value`() = withLocationsApplication {
application.install(DataConversion) {
convert(LocationEnum::class) {
encode { if (it == null) emptyList() else listOf((it as LocationEnum).name.toLowerCase()) }
decode { values, type -> LocationEnum.values().first { it.name.toLowerCase() in values } }
}
}
application.routing {
get<LocationWithEnum> {
call.respondText(call.locations.resolve<LocationWithEnum>(LocationWithEnum::class, call).e.name)
}
}
urlShouldBeHandled("/?e=a", "A")
urlShouldBeHandled("/?e=b", "B")
}
You can easily access the DataConversion service, from any call with:
val dataConversion = call.conversionService
interface ConversionService {
fun fromValues(values: List<String>, type: Type): Any?
fun toValues(value: Any?): List<String>
}
class DelegatingConversionService(private val klass: KClass<*>) : ConversionService {
fun decode(converter: (values: List<String>, type: Type) -> Any?)
fun encode(converter: (value: Any?) -> List<String>)
}