Kotlin中使用Jackson JsonSubType实现嵌套子类反序列化失败问题

我有一个消息投递系统，支持推送通知、SMS等类型，每种类型还包含各自的子类型（例如SMS分为Irancell、Mediana等）。我希望使用JsonSubType识别消息对应的类并调用对应发送机制，但序列化MedianaSmsMessage后，无法将其反序列化为MessageForDelivery类型。

相关代码 #

MedianaSmsMessage类 #

class MedianaSmsMessage(
    override val receiver: String,
    override val message: Message,
    override val app: App,
    override val requester: DeliveryRequester,
    override val deliveryProviderId: String,
    override val smsDeliveryType: String = "MEDIANA",
) : SmsMessageForDelivery()

SmsMessageForDelivery抽象类 #

@JsonTypeInfo(use = JsonTypeInfo.Id.NAME, include = JsonTypeInfo.As.EXISTING_PROPERTY, property = "smsDeliveryType", visible = true)
@JsonSubTypes(
    JsonSubTypes.Type(value = MedianaSmsMessage::class, name = "MEDIANA"),
    JsonSubTypes.Type(value = IrancellSmsMessage::class, name = "IRANCELL"),
    JsonSubTypes.Type(value = MobinnetSmsMessage::class, name = "MOBINNET"),
)
abstract class SmsMessageForDelivery : MessageForDelivery() {
    abstract override val receiver: String
    abstract override val message: Message
    override val deliveryType: DeliveryType = DeliveryType.SMS
    abstract override val app: App
    abstract override val requester: DeliveryRequester
    abstract override val deliveryProviderId: String
    abstract val smsDeliveryType: String
}

MessageForDelivery抽象类 #

@JsonTypeInfo(use = JsonTypeInfo.Id.NAME, include = JsonTypeInfo.As.EXISTING_PROPERTY, property = "deliveryType", visible = true)
@JsonSubTypes(
    JsonSubTypes.Type(value = PushMessageForDelivery::class, name = "APP_PUSH"),
    JsonSubTypes.Type(value = WebHookMessageForDelivery::class, name = "WEBHOOK"),
    JsonSubTypes.Type(value = EmailMessageForDelivery::class, name = "EMAIL"),
    JsonSubTypes.Type(value = SmsMessageForDelivery::class, name = "SMS"),
)

abstract class MessageForDelivery {
    abstract val receiver: String
    abstract val message: Message
    abstract val deliveryType: DeliveryType
    abstract val app: App
    abstract val requester: DeliveryRequester
    abstract val deliveryProviderId: String
}

测试代码 #

@PostConstruct
fun test(){
    val content = "{\"smsDeliveryType\":\"MEDIANA\",\"receiver\":\"+9891312331\",\"message\":{\"title\":\"sms-title\",\"body\":\"test\",\"link\":null,\"url\":null,\"icon\":null,\"images\":[],\"buttons\":[]},\"app\":{\"appId\":\"test\"},\"requester\":{\"type\":\"CAMPAIGN\",\"id\":\"63e8b35acedd7f451fd0da14\"},\"deliveryProviderId\":\"Mediana\",\"deliveryType\":\"SMS\"}"
    val medianaSms = mapper.readValue(
        content,
        MedianaSmsMessage::class.java
    )
    val t = mapper.writeValueAsString(medianaSms)
    val test = mapper.readValue(t, MessageForDelivery::class.java)
    println(test)
}

错误信息 #

无法构造`ir.pegahtech.metrix.delivery.push.services.models.message.sms.SmsMessageForDelivery`的实例（不存在默认构造函数等创建器）：抽象类型要么需要映射到具体类型，要么有自定义反序列化器，或者包含额外的类型信息

解决方案 #

问题根源是Jackson仅完成了MessageForDelivery到SmsMessageForDelivery的第一层多态解析，但SmsMessageForDelivery作为抽象类，Jackson无法自动识别其下的具体子类（如MedianaSmsMessage），以下是三种可行解决办法：

方案一：直接在顶层父类注册所有SMS子类 #

修改MessageForDelivery的@JsonSubTypes注解，把所有SMS具体子类直接加入注册列表，让Jackson能通过deliveryType和smsDeliveryType的组合完成完整解析：

@JsonTypeInfo(use = JsonTypeInfo.Id.NAME, include = JsonTypeInfo.As.EXISTING_PROPERTY, property = "deliveryType", visible = true)
@JsonSubTypes(
    JsonSubTypes.Type(value = PushMessageForDelivery::class, name = "APP_PUSH"),
    JsonSubTypes.Type(value = WebHookMessageForDelivery::class, name = "WEBHOOK"),
    JsonSubTypes.Type(value = EmailMessageForDelivery::class, name = "EMAIL"),
    // 直接注册所有SMS具体子类
    JsonSubTypes.Type(value = MedianaSmsMessage::class, name = "SMS"),
    JsonSubTypes.Type(value = IrancellSmsMessage::class, name = "SMS"),
    JsonSubTypes.Type(value = MobinnetSmsMessage::class, name = "SMS"),
)
abstract class MessageForDelivery {
    // 原有代码不变
}

方案二：启用全局多态类型解析 #

配置ObjectMapper启用全局默认类型解析，Jackson会自动在序列化JSON中添加类型标识字段，无需手动维护子类列表，但会改变JSON结构：

val mapper = ObjectMapper()
    .registerModule(KotlinModule())
    .enableDefaultTyping(ObjectMapper.DefaultTyping.NON_FINAL, JsonTypeInfo.As.PROPERTY)

方案三：自定义反序列化器 #

编写自定义反序列化器，手动根据deliveryType和smsDeliveryType字段选择对应的具体类，灵活性最高：

class MessageForDeliveryDeserializer : StdDeserializer<MessageForDelivery>(MessageForDelivery::class.java) {
    override fun deserialize(p: JsonParser, ctxt: DeserializationContext): MessageForDelivery {
        val node = p.codec.readTree<JsonNode>(p)
        val deliveryType = node["deliveryType"].asText()
        return when (deliveryType) {
            "SMS" -> {
                val smsType = node["smsDeliveryType"].asText()
                when (smsType) {
                    "MEDIANA" -> p.codec.treeToValue(node, MedianaSmsMessage::class.java)
                    "IRANCELL" -> p.codec.treeToValue(node, IrancellSmsMessage::class.java)
                    "MOBINNET" -> p.codec.treeToValue(node, MobinnetSmsMessage::class.java)
                    else -> throw IllegalArgumentException("未知SMS类型: $smsType")
                }
            }
            "APP_PUSH" -> p.codec.treeToValue(node, PushMessageForDelivery::class.java)
            "WEBHOOK" -> p.codec.treeToValue(node, WebHookMessageForDelivery::class.java)
            "EMAIL" -> p.codec.treeToValue(node, EmailMessageForDelivery::class.java)
            else -> throw IllegalArgumentException("未知投递类型: $deliveryType")
        }
    }
}

然后在MessageForDelivery类上添加注解指定反序列化器：

@JsonDeserialize(using = MessageForDeliveryDeserializer::class)
abstract class MessageForDelivery {
    // 原有代码不变
}

内容的提问来源于stack exchange，提问作者arianhf