Use pure-java HTTP client instead of OkHttp?

[exoego]

OkHttp v4 is written in Kotlin.
If we version up OkHttp to v4 or later, we need to depend on kotlin-stdlib transitively.

[xerial]

@exoego This can be a good approach to avoid dependency issues around okhttp and Kotlin. I've tested the pure-java HTTP client (available since Java9) at airframe-http and it works well out of the box https://github.com/wvlet/airframe/blob/master/airframe-http/.jvm/src/main/scala/wvlet/airframe/http/client/JavaHttpClientChannel.scala