OkHttpClient is final

What is the point of OkHttpClient be a final class?

Some frameworks, like spring, make intense use of proxies for almost everything.

I had a use case where I use to build the feign clients manually and now I’m trying to use spring-cloud-opentracing to do some distributed tracing.

One problem I’m facing is, on that package there’s a Aspect in order to decorate the client the their TracingClient, but the problem is: the aspect tries to make a proxy of the client implementation but the OkHttpClient is final.

tl;dr What is the possibility of making the OkHttpClient not final?

edit: The spring cloud opentracing feign can be found here: https://github.com/opentracing-contrib/java-spring-cloud/blob/master/instrument-starters/opentracing-spring-cloud-feign-starter/src/main/java/io/opentracing/contrib/spring/cloud/feign/FeignTracingAutoConfiguration.java#L80

[kdavisk6]

Based on my understanding of the history of this project and it’s modules, the Client interface is meant to be “open for extension, closed for modification” following the Open-Closed Principle. Both the ApacheHttpClient and the OkHttpClient are final in order to adhere to this.

With regards to OpenTracing, there is an OpenTracing implementation for Feign available that appears to indicate that you can use the provided OkHttpClient with OpenTracing

https://github.com/OpenFeign/feign-opentracing

In your particular case, you want to use Spring’s Open Tracing support for Spring Boot, which as you’ve pointed out, uses an Aspect to instrument a Feign client that is not using a TracingClient explicitly. Since you have mentioned that you are manually configuring Feign, if you use a TracingClient explicitly, the Aspect is not necessary.

GitHub github = Feign.builder()
                     .client(new TracingClient(new OkHttpClient(), tracer))
                     .target(GitHub.class, "https://api.github.com");

Looking at both feign-opentracing and the Spring project, if you want to use a provided Client, you must use TracingClient directly.

Now, with that said, I don’t see an issue with changing the current Client implementations away from final. Let’s ask the other contributors what they think.

@velo, @spencergibb, @adriancole Thoughts?

[williamokano]

Couldn’t do as you suggested.

I created a springboot autoconfiguration which creates a bean for TracingClient decorated with OkHttpClient. I think it’s probably for the best to keep OkHttpClient as final.