JsonEncoder

interface JsonEncoder : Encoder, CompositeEncoder

Encoder used by Json during serialization. This interface can be used to inject desired behaviour into a serialization process of Json.

Typical example of the usage:

// Class representing Either<Left|Right>
sealed class Either {
data class Left(val errorMsg: String) : Either()
data class Right(val data: Payload) : Either()
}

// Serializer injects custom behaviour by inspecting object content and writing
object EitherSerializer : KSerializer<Either> {
override val descriptor: SerialDescriptor = buildSerialDescriptor("package.Either", PolymorphicKind.SEALED) {
// ..
}

override fun deserialize(decoder: Decoder): Either {
val input = decoder as? JsonDecoder ?: throw SerializationException("This class can be decoded only by Json format")
val tree = input.decodeJsonElement() as? JsonObject ?: throw SerializationException("Expected JsonObject")
if ("error" in tree) return Either.Left(tree["error"]!!.jsonPrimitive.content)
return Either.Right(input.json.decodeFromJsonElement(Payload.serializer(), tree))
}

override fun serialize(encoder: Encoder, value: Either) {
val output = encoder as? JsonEncoder ?: throw SerializationException("This class can be encoded only by Json format")
val tree = when (value) {
is Either.Left -> JsonObject(mapOf("error" to JsonPrimitve(value.errorMsg)))
is Either.Right -> output.json.encodeToJsonElement(Payload.serializer(), value.data)
}
output.encodeJsonElement(tree)
}
}

Not stable for inheritance

JsonEncoder interface is not stable for inheritance in 3rd party libraries, as new methods might be added to this interface or contracts of the existing methods can be changed. Accepting this interface in your API methods, casting Encoder to JsonEncoder and invoking its methods is considered stable.

Functions

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open fun beginCollection(descriptor: SerialDescriptor, collectionSize: Int): CompositeEncoder
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abstract fun beginStructure(descriptor: SerialDescriptor): CompositeEncoder
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abstract fun encodeBoolean(value: Boolean)
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abstract fun encodeBooleanElement(    descriptor: SerialDescriptor,     index: Int,     value: Boolean)
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abstract fun encodeByte(value: Byte)
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abstract fun encodeByteElement(    descriptor: SerialDescriptor,     index: Int,     value: Byte)
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abstract fun encodeChar(value: Char)
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abstract fun encodeCharElement(    descriptor: SerialDescriptor,     index: Int,     value: Char)
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abstract fun encodeDouble(value: Double)
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abstract fun encodeDoubleElement(    descriptor: SerialDescriptor,     index: Int,     value: Double)
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abstract fun encodeEnum(enumDescriptor: SerialDescriptor, index: Int)
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abstract fun encodeFloat(value: Float)
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abstract fun encodeFloatElement(    descriptor: SerialDescriptor,     index: Int,     value: Float)
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abstract fun encodeInline(descriptor: SerialDescriptor): Encoder
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abstract fun encodeInlineElement(descriptor: SerialDescriptor, index: Int): Encoder
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abstract fun encodeInt(value: Int)
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abstract fun encodeIntElement(    descriptor: SerialDescriptor,     index: Int,     value: Int)
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abstract fun encodeJsonElement(element: JsonElement)

Appends the given JSON element to the current output. This method is allowed to invoke only as the part of the whole serialization process of the class, calling this method after invoking beginStructure or any encode* method will lead to unspecified behaviour and may produce an invalid JSON result. For example:

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abstract fun encodeLong(value: Long)
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abstract fun encodeLongElement(    descriptor: SerialDescriptor,     index: Int,     value: Long)
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open fun encodeNotNullMark()
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abstract fun encodeNull()
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abstract fun <T : Any> encodeNullableSerializableElement(    descriptor: SerialDescriptor,     index: Int,     serializer: SerializationStrategy<T>,     value: T?)
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open fun <T : Any> encodeNullableSerializableValue(serializer: SerializationStrategy<T>, value: T?)
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abstract fun <T> encodeSerializableElement(    descriptor: SerialDescriptor,     index: Int,     serializer: SerializationStrategy<T>,     value: T)
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open fun <T> encodeSerializableValue(serializer: SerializationStrategy<T>, value: T)
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abstract fun encodeShort(value: Short)
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abstract fun encodeShortElement(    descriptor: SerialDescriptor,     index: Int,     value: Short)
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abstract fun encodeString(value: String)
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abstract fun encodeStringElement(    descriptor: SerialDescriptor,     index: Int,     value: String)
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abstract fun endStructure(descriptor: SerialDescriptor)
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open fun shouldEncodeElementDefault(descriptor: SerialDescriptor, index: Int): Boolean

Properties

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abstract val json: Json

An instance of the current Json.

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abstract val serializersModule: SerializersModule