java - 使用 jacksonObjectMapper 将 JSON 反序列化为不同类型

Question

假设我从服务器收到一个 JSON 错误，该错误可以采用两种不同的结构:

{"errorMessage": "This action is unauthorized."}

或

{"errorMessage":{"changePassword":"Old password is incorrect."}}

如何反序列化这种json？

我尝试过的

我尝试拥有抽象类“Error”和两个子类:

abstract class Error() {}

data class SingleError(val errorMessage: String) : Error() 

data class MultiError(val errorMessage: Map<String, String>) : Error() 

然后我尝试:

jacksonObjectMapper().readValue<Error>(response.body)

反序列化，但我有异常(exception):

com.fasterxml.jackson.databind.exc.InvalidDefinitionException: Cannot construct instance of `com.fifth_llc.siply.main.request.Forbidden$Error` (no Creators, like default construct, exist): abstract types either need to be mapped to concrete types, have custom deserializer, or contain additional type information
     at [Source: (String)"{"errorMessage":{"changePassword":"Old password is incorrect."}}"; line: 1, column: 1]

我也尝试过 JsonDeserialize annotaiton，但如果我想解析为具体类型，我似乎可以使用它:

@JsonDeserialize(`as` = MultiError::class)

有什么帮助吗？

Answer 1

自定义解串器方法:

sealed class Error() {
    data class SingleError(val errorMessage: String) : Error()
    data class MultiError(val errorMessage: Map<String, String>) : Error()
}
...
class ErrorDeserializer : StdDeserializer<Error>(Error::class.java) {

    companion object {
        private val MAP_TYPE_REFERENCE = object : TypeReference<Map<String, String>>() {}
    }

    @Throws(IOException::class, JsonProcessingException::class)
    override fun deserialize(jp: JsonParser, ctxt: DeserializationContext): Error {
        val mapper = jp.codec as ObjectMapper
        val node: JsonNode = mapper.readTree(jp)
        val msgNode = node.get("errorMessage")
        if (msgNode.isValueNode) {
            val errorMsg = msgNode.asText()
            return Error.SingleError(errorMsg)
        } else {
            val errorMsgs = mapper.readValue<Map<String, String>>(msgNode.toString(), 
                    MAP_TYPE_REFERENCE)
            return Error.MultiError(errorMsgs)
        }
    }
}

用法:

val mapper = ObjectMapper()
val module = SimpleModule().addDeserializer(Error::class.java, ErrorDeserializer())
mapper.registerModule(module)

val error = mapper.readValue<Error>("json content", Error::class.java)
when (error) {
    is Error.SingleError -> {
        // error.errorMessage
    }
    is Error.MultiError -> {
        // error.errorMessage
    }
}