# Kotlin JSON wrapper for Jackson **URL:** \ **Category:** Uncategorized\ **Created:** [April 6, 2014, 11:17pm UTC](https://discuss.kotlinlang.org/t/kotlin-json-wrapper-for-jackson/604 "2014-04-06T23:17:57Z")\ **Posts on this page:** 8\ **Page:** 1
**Author:** ![andrewoma](https://avatars.discourse-cdn.com/v4/letter/a/c37758/32.png) [@andrewoma](https://discuss.kotlinlang.org/u/andrewoma)\ **Post date:** [April 6, 2014, 11:17pm UTC](https://discuss.kotlinlang.org/t/kotlin-json-wrapper-for-jackson/604/1 "2014-04-06T23:17:57Z")
Greeting all, I’ve done a proof of concept JSON wrapper for Jackson based on Play’s JSON support and ended up with: [https://github.com/andrewoma/kson](https://github.com/andrewoma/kson) It’s the result of an afternoon’s hacking, so it’s definitely not a production library. However, it seemed promising, so thought I’d publish it as is. Here’s an example from [https://github.com/andrewoma/kson/blob/master/kson/src/test/java/com/github/andrewoma/kson/JsValueTest.kt](https://github.com/andrewoma/kson/blob/master/kson/src/test/java/com/github/andrewoma/kson/JsValueTest.kt) ``` val value = JsObject(            "firstName" to "Andrew".json,            "lastName" to "O'Malley".json,            "age" to 21.json,            "adult" to true.json,            "address" to JsObject(                    "number" to "88".json,                    "street" to "Chapel Street".json,                    "suburb" to "Windsor".json,                    "state" to "VIC".json,                    "postCode" to "3181".json            ),            "pets" to JsArray(listOf(                    JsObject(                            "kind" to "dog".json,                            "name" to "Rover".json                    ),                    JsObject(                            "kind" to "cat".json,                            "name" to "Kitty".json                    )            )            )   ) ``` I’m still keen to experiment with some kind of builder syntax (or hear of other experiments - I know about klaxon). A question for the Kotlin devs: is the conversion operator still planned for Kotlin? See [http://youtrack.jetbrains.com/issue/KT-1752#comment=27-318887](http://youtrack.jetbrains.com/issue/KT-1752#comment=27-318887) If feel uneasy adding extension functions and properties to base types like String. A conversion operator (with the correct precedence) would allow things like the following without possible namespace clashes: ```kotlin fun String.convert() : JsValue = JsString(this) ``` ```kotlin ``` ---
**Author:** ![abreslav](https://sea1.discourse-cdn.com/flex019/user_avatar/discuss.kotlinlang.org/abreslav/32/8279_2.png) [@abreslav](https://discuss.kotlinlang.org/u/abreslav)\ **Post date:** [April 7, 2014, 6:40am UTC](https://discuss.kotlinlang.org/t/kotlin-json-wrapper-for-jackson/604/2 "2014-04-07T06:40:19Z")
Minor suggestions: - JsArray could take a vararg parameter, not a list - Maybe shorten ".json" to ".js" The conversion operator we are not yet sure about. I'd say in this case having a ".js" suffix would be nearly the same as the conversion operator ---
**Author:** ![andrewoma](https://avatars.discourse-cdn.com/v4/letter/a/c37758/32.png) [@andrewoma](https://discuss.kotlinlang.org/u/andrewoma)\ **Post date:** [April 7, 2014, 7:56am UTC](https://discuss.kotlinlang.org/t/kotlin-json-wrapper-for-jackson/604/3 "2014-04-07T07:56:15Z")
Hi Andrey, Thanks for the feedback and update on the conversion operator status. I actually tried vararg for JsArray first and it does make the example above prettier. However, it means using JsArray(\*list.copyToArrary()) when using it for non-builder use-cases and I figure these would be the norm for arrays. I guess I’ll add a function to support both styles. Off-topic: I think you made a great call to drop full-blown pattern matching in Kotlin. I ported some of the serialization code from Scala that used pattern matching extensively and I think the Kotlin port is more readable without it. Cheers, Andrew ---
**Author:** ![abreslav](https://sea1.discourse-cdn.com/flex019/user_avatar/discuss.kotlinlang.org/abreslav/32/8279_2.png) [@abreslav](https://discuss.kotlinlang.org/u/abreslav)\ **Post date:** [April 7, 2014, 9:34am UTC](https://discuss.kotlinlang.org/t/kotlin-json-wrapper-for-jackson/604/4 "2014-04-07T09:34:32Z")
> However, it means using JsArray(\*list.copyToArrary()) when using it for non-builder use-cases and I figure these would be the norm for arrays. I guess I'll add a function to support both styles. Yes, I think you can provide two overloaded versions to avoid this problem. > Off-topic: I think you made a great call to drop full-blown pattern matching in Kotlin. I ported some of the serialization code from Scala that used pattern matching extensively and I think the Kotlin port is more readable without it. Thanks for the feedback! Could you provide us with a side-by-side Scala and Kotlin code for comparison? ---
**Author:** ![andrewoma](https://avatars.discourse-cdn.com/v4/letter/a/c37758/32.png) [@andrewoma](https://discuss.kotlinlang.org/u/andrewoma)\ **Post date:** [April 7, 2014, 10:21am UTC](https://discuss.kotlinlang.org/t/kotlin-json-wrapper-for-jackson/604/5 "2014-04-07T10:21:33Z")
Hi Andrey, > However, it means using JsArray(\*list.copyToArrary()) when using it for non-builder use-cases and I figure these would be the norm for arrays. I guess I'll add a function to support both styles. > > Yes, I think you can provide two overloaded versions to avoid this problem. Yep, I've provided "secondary constructors" via functions as follows: ```kotlin public fun JsArray(vararg values: JsValue): JsValue = JsArray(values.toList()) public data class JsArray(val values: List) : JsValue() ``` I’ve also renamed .json to .js and agree it’s better (and committed to github). So the current version looks like this: ```kotlin   val value = JsObject(            "firstName" to "Andrew".js,            "lastName" to "O'Malley".js,            "age" to 21.js,            "adult" to true.js,            "address" to JsObject(                    "number" to "88".js,                    "street" to "Chapel Street".js,                    "suburb" to "Windsor".js,                    "state" to "VIC".js,                    "postCode" to "3181".js            ),            "pets" to JsArray(                    JsObject(                            "kind" to "dog".js,                            "name" to "Rover".js                    ),                    JsObject(                            "kind" to "cat".js,                            "name" to "Kitty".js                    )            )   ) ``` > Off-topic: I think you made a great call to drop full-blown pattern matching in Kotlin. I ported some of the serialization code from Scala that used pattern matching extensively and I think the Kotlin port is more readable without it. > > Thanks for the feedback! Could you provide us with a side-by-side Scala and Kotlin code for comparison? Kotlin: [https://github.com/andrewoma/kson/blob/master/kson/src/main/java/com/github/andrewoma/kson/KsonModule.kt](https://github.com/andrewoma/kson/blob/master/kson/src/main/java/com/github/andrewoma/kson/KsonModule.kt) Scala: [https://github.com/playframework/playframework/blob/master/framework/src/play-json/src/main/scala/play/api/libs/json/JsValue.scala](https://github.com/playframework/playframework/blob/master/framework/src/play-json/src/main/scala/play/api/libs/json/JsValue.scala) Compare the deserialize methods: - The cool thing is both are completely type safe and no casting is required - When porting, I found the Scala one confusing to unravel: - It matches on the same token multiple times (for expected and error cases) - It destructures lists as part of the matching, effectively popping off the stack - The function return is combination of matching plus guards, plus defaulting - The matching introduces a bunch of new variable names in the match, but the Kotlin version can just use the same variable (automatically cast) Naturally, I’m biased as I ported the Kotlin one, but I find it easier to follow without all the matching. Cheers, Andrew ---
**Author:** ![abreslav](https://sea1.discourse-cdn.com/flex019/user_avatar/discuss.kotlinlang.org/abreslav/32/8279_2.png) [@abreslav](https://discuss.kotlinlang.org/u/abreslav)\ **Post date:** [April 7, 2014, 10:36am UTC](https://discuss.kotlinlang.org/t/kotlin-json-wrapper-for-jackson/604/6 "2014-04-07T10:36:45Z")
Thanks again ---
**Author:** ![bashor](https://sea1.discourse-cdn.com/flex019/user_avatar/discuss.kotlinlang.org/bashor/32/1431_2.png) [@bashor](https://discuss.kotlinlang.org/u/bashor)\ **Post date:** [April 7, 2014, 11:49am UTC](https://discuss.kotlinlang.org/t/kotlin-json-wrapper-for-jackson/604/7 "2014-04-07T11:49:59Z")
Probably [this blogpost](http://hadihariri.com/2013/05/29/creating-builders-in-kotlin-the-results-of-the-kotlin-workshop/) will be interesting for You, if you didn't see it already. ---
**Author:** ![andrewoma](https://avatars.discourse-cdn.com/v4/letter/a/c37758/32.png) [@andrewoma](https://discuss.kotlinlang.org/u/andrewoma)\ **Post date:** [April 7, 2014, 1:33pm UTC](https://discuss.kotlinlang.org/t/kotlin-json-wrapper-for-jackson/604/8 "2014-04-07T13:33:40Z")
Thanks for that - I hadn't seen it. There's some interesting ideas in there. I might try to reproduce a couple and see how they fare. Some certainly look cleaner than my experiment, but I have some doubts as to whether they guarantee integrity, allow traversal, compose etc. Cheers, Andrew