列表的自定义 KotlinX 序列化程序 class
Custom KotlinX Serializer for List class
我想制作一个自定义列表序列化程序,它将安全地解析无效的 json 数组。示例:Int 列表 [1, "invalid_int", 2]
应解析为 [1, 2]
。
我制作了一个序列化程序并将其添加到 Json 提供程序,但是序列化在第一个元素之后一直失败并且无法继续,所以我得到了 1 个元素的列表 [1]
,我该如何正确处理无效元素所以解码器会继续解析其他元素?
class SafeListSerializerStack<E>(val elementSerializer: KSerializer<E>) : KSerializer<List<E>> {
override val descriptor: SerialDescriptor = ListSerializer(elementSerializer).descriptor
override fun serialize(encoder: Encoder, value: List<E>) {
val size = value.size
val composite = encoder.beginCollection(descriptor, size)
val iterator = value.iterator()
for (index in 0 until size) {
composite.encodeSerializableElement(descriptor, index, elementSerializer, iterator.next())
}
composite.endStructure(descriptor)
}
override fun deserialize(decoder: Decoder): List<E> {
val arrayList = arrayListOf<E>()
try {
val startIndex = arrayList.size
val messageBuilder = StringBuilder()
val compositeDecoder = decoder.beginStructure(descriptor)
while (true) {
val index = compositeDecoder.decodeElementIndex(descriptor) // fails here on number 2
if (index == CompositeDecoder.DECODE_DONE) {
break
}
try {
arrayList.add(index, compositeDecoder.decodeSerializableElement(descriptor, startIndex + index, elementSerializer))
} catch (exception: Exception) {
exception.printStackTrace() // falls here when "invalid_int" is parsed, it's ok
}
}
compositeDecoder.endStructure(descriptor)
if (messageBuilder.isNotBlank()) {
println(messageBuilder.toString())
}
} catch (exception: Exception) {
exception.printStackTrace() // falls here on number 2
}
return arrayList
}
}
解析无效元素后发生错误,并在 compositeDecoder.decodeElementIndex(descriptor)
行抛出异常:
kotlinx.serialization.json.internal.JsonDecodingException: Unexpected JSON token at offset 4: Expected end of the array or comma
JSON input: [1, "invalid_int", 2]
我觉得它应该“吞下”无效元素并继续移动,但它却卡住了,无法继续解析,这对我来说没有意义。
这可以在没有自定义序列化程序的情况下完成。只需将所有内容解析为 String
(指定 isLenient = true
以允许不带引号的字符串),然后将所有有效整数转换为 Int
:
fun main() {
val input = "[1, \"invalid_int\", 2]"
val result: List<Int> = Json { isLenient = true }
.decodeFromString<List<String>>(input)
.mapNotNull { it.toIntOrNull() }
println(result) // [1, 2]
}
在更通用的情况下(当列表是一个字段时 and/or 它的元素不简单 Int
s),您将需要一个自定义序列化程序:
class SafeListSerializerStack<E>(private val elementSerializer: KSerializer<E>) : KSerializer<List<E>> {
private val listSerializer = ListSerializer(elementSerializer)
override val descriptor: SerialDescriptor = listSerializer.descriptor
override fun serialize(encoder: Encoder, value: List<E>) {
listSerializer.serialize(encoder, value)
}
override fun deserialize(decoder: Decoder): List<E> = with(decoder as JsonDecoder) {
decodeJsonElement().jsonArray.mapNotNull {
try {
json.decodeFromJsonElement(elementSerializer, it)
} catch (e: SerializationException) {
e.printStackTrace()
null
}
}
}
}
请注意,此解决方案仅适用于 Json
格式的反序列化,并且需要 kotlinx.serialization
1.2.0+
找到方法,我们可以从解码器中提取 json 数组,因为我们使用 Json 来解析它
override fun deserialize(decoder: Decoder): List<E> {
val jsonInput = decoder as? JsonDecoder
?: error("Can be deserialized only by JSON")
val rawJson = jsonInput.decodeJsonElement()
if (rawJson !is JsonArray) {
return arrayListOf()
}
val jsonArray = rawJson.jsonArray
val jsonParser = jsonInput.json
val arrayList = ArrayList<E>(jsonArray.size)
jsonArray.forEach { jsonElement ->
val result = readElement(jsonParser, jsonElement)
when {
result.isSuccess -> arrayList.add(result.getOrThrow())
result.isFailure -> Log.d("ERROR", "error parsing array")
}
}
arrayList.trimToSize()
return arrayList
}
private fun readElement(json: Json, jsonElement: JsonElement): Result<E> {
return try {
Result.success(json.decodeFromJsonElement(elementSerializer, jsonElement))
} catch (exception: Exception) {
Result.failure(exception)
}
}
我想制作一个自定义列表序列化程序,它将安全地解析无效的 json 数组。示例:Int 列表 [1, "invalid_int", 2]
应解析为 [1, 2]
。
我制作了一个序列化程序并将其添加到 Json 提供程序,但是序列化在第一个元素之后一直失败并且无法继续,所以我得到了 1 个元素的列表 [1]
,我该如何正确处理无效元素所以解码器会继续解析其他元素?
class SafeListSerializerStack<E>(val elementSerializer: KSerializer<E>) : KSerializer<List<E>> {
override val descriptor: SerialDescriptor = ListSerializer(elementSerializer).descriptor
override fun serialize(encoder: Encoder, value: List<E>) {
val size = value.size
val composite = encoder.beginCollection(descriptor, size)
val iterator = value.iterator()
for (index in 0 until size) {
composite.encodeSerializableElement(descriptor, index, elementSerializer, iterator.next())
}
composite.endStructure(descriptor)
}
override fun deserialize(decoder: Decoder): List<E> {
val arrayList = arrayListOf<E>()
try {
val startIndex = arrayList.size
val messageBuilder = StringBuilder()
val compositeDecoder = decoder.beginStructure(descriptor)
while (true) {
val index = compositeDecoder.decodeElementIndex(descriptor) // fails here on number 2
if (index == CompositeDecoder.DECODE_DONE) {
break
}
try {
arrayList.add(index, compositeDecoder.decodeSerializableElement(descriptor, startIndex + index, elementSerializer))
} catch (exception: Exception) {
exception.printStackTrace() // falls here when "invalid_int" is parsed, it's ok
}
}
compositeDecoder.endStructure(descriptor)
if (messageBuilder.isNotBlank()) {
println(messageBuilder.toString())
}
} catch (exception: Exception) {
exception.printStackTrace() // falls here on number 2
}
return arrayList
}
}
解析无效元素后发生错误,并在 compositeDecoder.decodeElementIndex(descriptor)
行抛出异常:
kotlinx.serialization.json.internal.JsonDecodingException: Unexpected JSON token at offset 4: Expected end of the array or comma
JSON input: [1, "invalid_int", 2]
我觉得它应该“吞下”无效元素并继续移动,但它却卡住了,无法继续解析,这对我来说没有意义。
这可以在没有自定义序列化程序的情况下完成。只需将所有内容解析为 String
(指定 isLenient = true
以允许不带引号的字符串),然后将所有有效整数转换为 Int
:
fun main() {
val input = "[1, \"invalid_int\", 2]"
val result: List<Int> = Json { isLenient = true }
.decodeFromString<List<String>>(input)
.mapNotNull { it.toIntOrNull() }
println(result) // [1, 2]
}
在更通用的情况下(当列表是一个字段时 and/or 它的元素不简单 Int
s),您将需要一个自定义序列化程序:
class SafeListSerializerStack<E>(private val elementSerializer: KSerializer<E>) : KSerializer<List<E>> {
private val listSerializer = ListSerializer(elementSerializer)
override val descriptor: SerialDescriptor = listSerializer.descriptor
override fun serialize(encoder: Encoder, value: List<E>) {
listSerializer.serialize(encoder, value)
}
override fun deserialize(decoder: Decoder): List<E> = with(decoder as JsonDecoder) {
decodeJsonElement().jsonArray.mapNotNull {
try {
json.decodeFromJsonElement(elementSerializer, it)
} catch (e: SerializationException) {
e.printStackTrace()
null
}
}
}
}
请注意,此解决方案仅适用于 Json
格式的反序列化,并且需要 kotlinx.serialization
1.2.0+
找到方法,我们可以从解码器中提取 json 数组,因为我们使用 Json 来解析它
override fun deserialize(decoder: Decoder): List<E> {
val jsonInput = decoder as? JsonDecoder
?: error("Can be deserialized only by JSON")
val rawJson = jsonInput.decodeJsonElement()
if (rawJson !is JsonArray) {
return arrayListOf()
}
val jsonArray = rawJson.jsonArray
val jsonParser = jsonInput.json
val arrayList = ArrayList<E>(jsonArray.size)
jsonArray.forEach { jsonElement ->
val result = readElement(jsonParser, jsonElement)
when {
result.isSuccess -> arrayList.add(result.getOrThrow())
result.isFailure -> Log.d("ERROR", "error parsing array")
}
}
arrayList.trimToSize()
return arrayList
}
private fun readElement(json: Json, jsonElement: JsonElement): Result<E> {
return try {
Result.success(json.decodeFromJsonElement(elementSerializer, jsonElement))
} catch (exception: Exception) {
Result.failure(exception)
}
}