Spring Boot serialize text/javascript to JSON

Question

I created the following Kotlin data class:

@JsonInclude(JsonInclude.Include.NON_NULL)
public data class ITunesArtist(val artistName: String, 
    val artistId: Long, val artistLinkUrl: URL)

(a data class is a Kotlin class that auto-generates equals, hashcode, toString etc at compile time - saves time).

Now I've tried populating it using Spring RestTemplate:

@Test
fun loadArtist()
{
    val restTemplate = RestTemplate()
    val artist = restTemplate.getForObject(
            "https://itunes.apple.com/search?term=howlin+wolf&entity=allArtist&limit=1", ITunesQueryResults::class.java);
    println("Got artist: $artist")
}

It fails with:

Could not extract response: no suitable HttpMessageConverter found for response type 
[class vampr.api.service.authorization.facebook.ITunesArtist] 
and content type [text/javascript;charset=utf-8]

Fair enough - the JSON object mapper was probably expecting mime-type of text/json. Other than telling RestTemplate to map to String::class.java, and then instantiating an instance of JacksonObjectMapper by hand, is there a way to tell my RestTemplate to treat the returned mime type as JSON?

Answer 1

Instead of providing defaults for all properties in your data class you can also use this: https://github.com/FasterXML/jackson-module-kotlin

This Jackson module will allow you to serialize and deserialize Kotlin's data classes without having to worry about providing an empty constructor.

In a Spring Boot Application you can register the module with a @Configuration class like so:

@Configuration
class KotlinModuleConfiguration {
    @Bean
    fun kotlinModule(): KotlinModule {
        return KotlinModule()
    }
}

Other than that you can also use the extension functions mentioned in the documentation to register the module with Jackson.

Besides supporting data classes you will also get support for several classes from the Kotlin stdlib, like Pair for example.