What is the simplest to use XML deserialization li...

# announcements

[Emil Orvik Kollstrøm]

What is the simplest to use XML deserialization library for Kotlin? Love Klaxon for JSON, but it does not support XML

[alex]

if you're on JVM you can use Jackson or any other popular deserializer library, including JVM (SAX/StAX/DOM parsers) itself.

[Stephan Schroeder]

So our team is using Jackson but also Spring so this is where we configure the jackson.XmlMapper:

@Configuration
class ImporterConfig {
    @Bean
    fun getXmlMapper(): XmlMapper = XmlMapper(JacksonXmlModule().apply {
        setDefaultUseWrapper(false)
        setXMLTextElementName(XMLTextName)
        // blank string to null
        addDeserializerForType<String> { parsed: String? ->
            if (parsed != null && parsed.isNotBlank()) {
                parsed
            } else {
                null
            }
        }
        // Boolean should also be converted from values "0"(false) and "1"(true)
        addDeserializerForType<Boolean> { parsed: String? ->
            parsed?.let{
                when(it.toLowerCase()) {
                    "0", "false" -> false
                    "1", "true" -> true
                    else -> null
                }
            }
        }
    }).apply {
        registerModule(KotlinModule())
        configure(MapperFeature.ACCEPT_CASE_INSENSITIVE_PROPERTIES, true)
        configure(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES, false)
    }

    companion object {
        const val XMLTextName = "xmlTextName"
    }
}

private inline fun <reified T : Any> JacksonXmlModule.addDeserializerForType(crossinline convert: (String?) -> T?) {
    this.addDeserializer(T::class.java, object : StdDeserializer<T>(T::class.java) {
        override fun deserialize(parser: JsonParser, context: DeserializationContext): T? {
            val result: String? = StringDeserializer.instance.deserialize(parser, context)
            return convert(result)
        }
    })
}

I’m pretty proud of my inline extension function with reified type parameter addDeserializerForType 🤓

[Stephan Schroeder]

If your wondering what XMLTextName is for, it’s for when you need to deserialise a tag that has a body, but also attributes. Assume you have a tag <Price currency="EUR" >23.99</Price> than the data class for that would look like this:

data class Price(
        val currency: String,
        @JacksonXmlText @JsonProperty(XMLTextName) val amount: Double
)

[Emil Orvik Kollstrøm]

Thanks!
Yes you can be proud @Stephan Schroeder, that thing is a beauty!