Upgrade to OkHttp 4.9.3

[larsgrefer]

I propose to update to OkHttp 4 for Spring Boot 2.2.x.

Despite being a new major version, it's binary and java-source compatible with OkHttp 3.
It even uses the Maven-Coordinates and the package name of OkHttp 3.

More information about this can be found here: https://square.github.io/okhttp/upgrading_to_okhttp_4/

[wilkinsona]

Thanks for the suggestion. I think the switch to OkHttp4 and the introduction of a dependency on Kotlin is too big a change to make in 2.2, particularly after RC. Furthermore, Spring Framework 5.2 compiles and tests against 3.x. Thanks anyway.

[membersound]

I cannot see the point here. I mean, the kotlin dependency is just pulled into the test scope then, not adding into the packaged project. So why not upgrading the library to 4.x?

[wilkinsona]

OkHttp is more than just the mock web server. It is also primarily used as an HTTP client in main application code. This means that moving to 4.x would result in Kotlin being pulled into the packaged project.

[membersound]

Oh ok, that's not what I expected, because as Spring is having RestTemplate and WebClient already, I thought okhttp is used for testing purpose only...

[scottfrederick]

RestTemplate and WebClient don't implement the HTTP transport layer directly, but delegate to external libraries like Apache HttpComponents, OkHttp, Netty, or simply java.net.HttpURLConnection to handle the transport layer.

See ClientHttpRequestFactory in Spring Framework and it's usages in RestTemplateBuilder in Spring Boot for more details.

[odin568]

@wilkinsona The issue is quite old and it was clear to have that rejected to that time.
Are there any plans in the meantime as quite some time passed?

[wilkinsona]

We don't have any plans to upgrade at this time. Spring Framework 5.3 continues to compile against 3.x and we continue to feel that version 4's Kotlin dependency is too large for Spring Boot to use that version by default.