How to create a CDI Interceptor which advises methods from a Feign client? - cdi

Question

I've been trying to figure out how to intercept methods defined in a Feign client with CDI (1.2) interceptors. I need to intercept the response value the client is returning, and extract data to log and remove some data prior to it being returned to the calling process.
I'm running a Weld 2.3 container which provides CDI 1.2. In it, I would like to create a CDI interceptor which is triggered everytime a call to filter() is made.
public interface MyRepository {
#RequestLine("POST /v1/data/policy/input_data_filtered")
JsonNode filter(Body body);
}
and a matching Producer method:
#Produces
public MyRepository repositoryProducer() {
return Feign.builder()
.client(new ApacheHttpClient())
.encoder(new JacksonEncoder(mapper))
.decoder(new JacksonDecoder(mapper))
.logger(new Slf4jLogger(MyRepository.class))
.logLevel(feign.Logger.Level.FULL)
.target(MyRepository.class, "http://localhost:9999");
}
I've tried the standard CDI interceptor way by creating an #InterceptorBinding and adding it to the interface definition, but that didn't work. I suspect because the interceptor must be applied to the CDI bean(proxy) and cannot be defined in an interface. I tried applying it to the repositoryProducer() method but that too was non functional.
I've read about the javax.enterprise.inject.spi.InterceptionFactory which is availabel in CDI 2.0, but I don't have access to it.
How can I do this in CDI 1.2? Or alternatively, is there a better interceptor pattern I can use that is built into Feign somehow?

Answer 1

The short, somewhat incorrect answer is: you cannot. InterceptionFactory is indeed how you would do it if you could.
The longer answer is something like this:
Use java.lang.reflect.Proxy to create a proxy implementation of the MyRepository interface.
Create an InvocationHandler that performs the interception around whatever methods you want.
Target Feign at that proxy implementation.