Using Type in JsonMapper

This is a comment by @unoexperto from an issue (https://github.com/tipsy/javalin/issues/1445#issuecomment-1007619810)

@tipsy Sorry for asking here, David, but I didn’t want to create another issue for a question. I’m using Moshi for json serialization. I see that io.javalin.plugin.json.JsonMapper.toJsonString() doesn’t carry type information about the object. As result I can’t serialize generic types such as List<Mytype<String>>. Ideally I’d like to see java.lang.reflect.Type to be an argument of toJsonString() and Context.json() become reified. Do you think it’s good idea ?

And perhaps existing Context functions that use Class<T> should use Type as well because it’s base type for both ParameterizedType and Class<T>.

[unoexperto]

@tipsy Hi David. Unfortunately I was pressured with deadline at the time so I ended up writing thin routing wrapper around reactor-netty-http for my restful api implementation. I’ll give javalin another try in a month or so.

[dzikoysk]

I’ve made a prototype of this feature in:

• https://github.com/javalin/javalin/pull/1657

Like I said, it’s not that beauty because we’ve made handling experience a little bit worse due to casts & unsafe generic signatures, but in the end it works.

As a side note, I think Moshi will be quite painful to use, because:

• It requires dedicated adapter for each signature, so you may need to create some kind of cache of adapters or you’ll pay a cost of creating a new adapter per each ctx.json call and it could impact your performance if it does sth expensive under the hood.
• Another thing is that it won’t work that with reified functions for e.g. lists, because you don’t have control over type generated by Kotlin compiler, so instead of java.util.List you’ll more likely end up with explicit implementation type like ArrayList/LinkedList/etc + their immutable wrappers and Moshi by default supports only interface types. As far as I’ve seen there’s no convenient solution, so you’ll need to use Types.newParameterizedType anyway for such scenarios instead of reified type, but it should work properly for regular records/data classes

– Edit Looks like we can’t add extra reified ctx.json, because it’ll be shadowed by base ctx.json anyway, so we could only expose the Type in json function to make it possible specify this parametrized type by hand. I mean you could write utility function like ctx.reifiedJson and use it on your own, but I’m talking in terms of official API.