Spring Cloud OpenFeign

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Spring Cloud OpenFeign

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1.2. Overriding Feign Defaults

A central concept in Spring Cloud’s Feign support is that of the named client. Each feign client is part of an ensemble of components that work together to contact a remote server on demand, and the ensemble has a name that you give it as an application developer using the @FeignClient annotation. Spring Cloud creates a new ensemble as an ApplicationContext on demand for each named client using FeignClientsConfiguration. This contains (amongst other things) an feign.Decoder, a feign.Encoder, and a feign.Contract. It is possible to override the name of that ensemble by using the contextId attribute of the @FeignClient annotation.

Spring Cloud lets you take full control of the feign client by declaring additional configuration (on top of the FeignClientsConfiguration) using @FeignClient. Example:

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

In this case the client is composed from the components already in FeignClientsConfiguration together with any in FooConfiguration (where the latter will override the former).

FooConfiguration does not need to be annotated with @Configuration. However, if it is, then take care to exclude it from any @ComponentScan that would otherwise include this configuration as it will become the default source for feign.Decoder, feign.Encoder, feign.Contract, etc., when specified. This can be avoided by putting it in a separate, non-overlapping package from any @ComponentScan or @SpringBootApplication, or it can be explicitly excluded in @ComponentScan. The serviceId attribute is now deprecated in favor of the name attribute. Using contextId attribute of the @FeignClient annotation in addition to changing the name of the ApplicationContext ensemble, it will override the alias of the client name and it will be used as part of the name of the configuration bean created for that client. Previously, using the url attribute, did not require the name attribute. Using name is now required.

Placeholders are supported in the name and url attributes.

@FeignClient(name = "${feign.name}", url = "${feign.url}") public interface StoreClient { //.. }

Spring Cloud Netflix provides the following beans by default for feign (BeanType beanName: ClassName):

Decoder feignDecoder: ResponseEntityDecoder (which wraps a SpringDecoder)

Encoder feignEncoder: SpringEncoder

Logger feignLogger: Slf4jLogger

Contract feignContract: SpringMvcContract

Feign.Builder feignBuilder: HystrixFeign.Builder

Client feignClient: if Ribbon is in the classpath and is enabled it is a LoadBalancerFeignClient, otherwise if Spring Cloud LoadBalancer is in the classpath, FeignBlockingLoadBalancerClient is used. If none of them is in the classpath, the default feign client is used.

spring-cloud-starter-openfeign supports both spring-cloud-starter-netflix-ribbon and spring-cloud-starter-loadbalancer. However, as they are optional dependencies, you need to make sure the one you want to use has been added to your project.

The OkHttpClient and ApacheHttpClient feign clients can be used by setting feign.okhttp.enabled or feign.httpclient.enabled to true, respectively, and having them on the classpath. You can customize the HTTP client used by providing a bean of either org.apache.http.impl.client.CloseableHttpClient when using Apache or okhttp3.OkHttpClient when using OK HTTP.

Spring Cloud OpenFeign does not provide the following beans by default for feign, but still looks up beans of these types from the application context to create the feign client:

Logger.Level

ErrorDecoder

Request.Options

Collection

SetterFactory

QueryMapEncoder

A bean of Retryer.NEVER_RETRY with the type Retryer is created by default, which will disable retrying. Notice this retrying behavior is different from the Feign default one, where it will automatically retry IOExceptions, treating them as transient network related exceptions, and any RetryableException thrown from an ErrorDecoder.

Creating a bean of one of those type and placing it in a @FeignClient configuration (such as FooConfiguration above) allows you to override each one of the beans described. Example:

@Configuration public class FooConfiguration { @Bean public Contract feignContract() { return new feign.Contract.Default(); } @Bean public BasicAuthRequestInterceptor basicAuthRequestInterceptor() { return new BasicAuthRequestInterceptor("user", "password"); } }

This replaces the SpringMvcContract with feign.Contract.Default and adds a RequestInterceptor to the collection of RequestInterceptor.

@FeignClient also can be configured using configuration properties.

application.yml

feign: client: config: feignName: connectTimeout: 5000 readTimeout: 5000 loggerLevel: full errorDecoder: com.example.SimpleErrorDecoder retryer: com.example.SimpleRetryer requestInterceptors: - com.example.FooRequestInterceptor - com.example.BarRequestInterceptor decode404: false encoder: com.example.SimpleEncoder decoder: com.example.SimpleDecoder contract: com.example.SimpleContract

Default configurations can be specified in the @EnableFeignClients attribute defaultConfiguration in a similar manner as described above. The difference is that this configuration will apply to all feign clients.

If you prefer using configuration properties to configured all @FeignClient, you can create configuration properties with default feign name.

application.yml

feign: client: config: default: connectTimeout: 5000 readTimeout: 5000 loggerLevel: basic

If we create both @Configuration bean and configuration properties, configuration properties will win. It will override @Configuration values. But if you want to change the priority to @Configuration, you can change feign.client.default-to-properties to false.

If you need to use ThreadLocal bound variables in your RequestInterceptor`s you will need to either set the thread isolation strategy for Hystrix to `SEMAPHORE or disable Hystrix in Feign.

application.yml

# To disable Hystrix in Feign feign: hystrix: enabled: false # To set thread isolation to SEMAPHORE hystrix: command: default: execution: isolation: strategy: SEMAPHORE

If we want to create multiple feign clients with the same name or url so that they would point to the same server but each with a different custom configuration then we have to use contextId attribute of the @FeignClient in order to avoid name collision of these configuration beans.

@FeignClient(contextId = "fooClient", name = "stores", configuration = FooConfiguration.class) public interface FooClient { //.. } @FeignClient(contextId = "barClient", name = "stores", configuration = BarConfiguration.class) public interface BarClient { //.. }

It is also possible to configure FeignClient not to inherit beans from the parent context. You can do this by overriding the inheritParentConfiguration() in a FeignClientConfigurer bean to return false:

@Configuration public class CustomConfiguration{ @Bean public FeignClientConfigurer feignClientConfigurer() { return new FeignClientConfigurer() { @Override public boolean inheritParentConfiguration() { return false; } }; } }

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