How to fine-tune the Spring Cloud Feign client?

问题:

The Spring Cloud doc says:

If Hystrix is on the classpath, by default Feign will wrap all methods with a circuit breaker.

1. That's good but how do I configure the Hystrix options to ignore certain exceptions? I've an ErrorDecoder implementation that maps HTTP status code to exceptions. If I put @HystrixCommand on the method, does Feign honor that?
2. Our requirement is to log various details about every HTTP call made out to dependencies. Currently I've a decorated RestTemplate that does this. From what I see in the code and based on Dave Syer's answer here, Feign does't use a RestTemplate. So how do I meet the logging requirement? The interface feign.Client looks promising, although I'm not entirely sure if that's the one to use.

回答1:

1. Feign doesn't honor @HystrixCommand and doesn't support ignoring exceptions. My suggestion is to disable feigns hystrix integration (feign.hystrix.enabled=false) and use hystrix outside of feign.
2. Feign supports RequestInterceptors that will give you a place to log. See the docs for more information.

Example:

@FeignClient(name = "stores", configuration = StoreConfiguration.class)
public interface StoreClient {
    //..
}

@Configuration
public class StoreConfiguration {

    @Bean
    public LoggingRequestInterceptor loggingRequestInterceptor() {
        return new LoggingRequestInterceptor();
    }
}

回答2:

You can write ErrorDecoder and throw HystrixBadRequestException (https://github.com/Netflix/Hystrix/wiki/How-To-Use#error-propagation) on exception that you want no to trigger the circuit breaker

回答3:

We use an own mime type for exceptions in such case so even error cases will be responded with http 200 but own mime type. Then we can intercept the 200er response in case of error mime type an rethrow the same exception as on server side by deserialisation from response error code without being trapped by a fallback. This works wirh Feign and some FeignBuildwr Magic

回答4:

Like @spencergibb said, Feign doesn't support ignoring exception now, for which I opened an enhancement request. As for my second requirement, a RequestInterceptor doesn't cut it because I need the response time, which the RequestInterceptor doesn't have access to. I ended up implementing the feign.Client and logging the time taken by the execute method. Most of the code is taken from feign.Client.Default, too bad that that class is not designed for extension. I then use my custom client in a FeignBuilder as follows:

@Bean
@Scope(SCOPE_PROTOTYPE)
public Feign.Builder feignBuilder() {
    return HystrixFeign.builder()
            .client(loggingEnabledFeignClient());
}

@Bean
Client loggingEnabledFeignClient() {
    return new LoggingEnabledFeignClient();
}