如何在 Jackson 中為包含泛型類型的列表創建自定義反序列化器？

Question

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如何在 Jackson 中為泛型類型創建自定義反序列化器？

我想知道如何采用它來解析

public static class Something {
    public static List<Wrapper<Person>> people;
}

這是我到目前為止所擁有的

internal class WithVisibilityDeserializer :
    JsonDeserializer<WithVisibility<*>>(), ContextualDeserializer {
    private var valueType: JavaType? = null

    @Throws(JsonMappingException::class)
    override fun createContextual(
        ctxt: DeserializationContext,
        property: BeanProperty
    ): JsonDeserializer<*> {
        val wrapperType = property.type
        val valueType = wrapperType.containedType(0)
        val deserializer = WithVisibilityDeserializer()
        deserializer.valueType = valueType
        return deserializer
    }

    @Throws(IOException::class)
    override fun deserialize(parser: JsonParser, ctxt: DeserializationContext): WithVisibility<*> {
        val value: Any? = ctxt.readValue<Any>(parser, valueType)
        return WithVisibility(
            value = value,
            visibility = false
        )
    }
}

並且在嘗試反序列化其中的一些內容時，我得到了一個 NPE

data class ViewSelectionFieldTypes(
    @JacksonXmlElementWrapper(localName = "Types", useWrapping = false)
    @JacksonXmlProperty(localName = "Type")
    val type: List<WithVisibility<String>>
)

Answer 1

這里的關鍵是

al valueType = if (!wrapperType.isCollectionLikeType) {
            wrapperType.containedType(0)
        } else {
            // This is needed because there is a List that contains the WithVisibility (List<WithVisibility<String>>)
            wrapperType.containedType(0).containedType(0)
        }

解決方案：

internal class WithVisibilityDeserializer :
    JsonDeserializer<WithVisibility<*>>(), ContextualDeserializer {
    private var valueType: JavaType? = null

    @Throws(JsonMappingException::class)
    override fun createContextual(
        ctxt: DeserializationContext,
        property: BeanProperty
    ): JsonDeserializer<*> {
        val wrapperType = property.type
        val valueType = if (!wrapperType.isCollectionLikeType) {
            wrapperType.containedType(0)
        } else {
            // This is needed because there is a List that contains the WithVisibility (List<WithVisibility<String>>)
            wrapperType.containedType(0).containedType(0)
        }
        val deserializer = WithVisibilityDeserializer()
        deserializer.valueType = valueType
        return deserializer
    }

    @Throws(IOException::class)
    override fun deserialize(parser: JsonParser, ctxt: DeserializationContext): WithVisibility<*> {
        val value: Any? = ctxt.readValue<Any>(parser, valueType)
        return WithVisibility(
            value = value,
            visibility = false
        )
    }
}