springcloud之feign

springcloud之feign

a declarative REST client for Spring Boot apps

Dependency

spring-cloud-starter-openfeign

Code

• @EnableFeignClients
• declare a Feign client using the @FeignClient annotation

@SpringBootApplication
@EnableFeignClients
public class ExampleApplication {

    public static void main(String[] args) {
        SpringApplication.run(ExampleApplication.class, args);
    }
}

@FeignClient(value = "jplaceholder", url = "https://jsonplaceholder.typicode.com/")
public interface JSONPlaceHolderClient {

    @RequestMapping(method = RequestMethod.GET, value = "/posts")
    List<Post> getPosts();

    @RequestMapping(method = RequestMethod.GET, value = "/posts/{postId}", produces = "application/json")
    Post getPostById(@PathVariable("postId") Long postId);
}

Configuration

FeignClientsConfiguration

• Decoder – ResponseEntityDecoder, which wraps SpringDecoder, used to decode the Response
• Encoder – SpringEncoder, used to encode the RequestBody
• Logger – Slf4jLogger is the default logger used by Feign
• Feign-Builder – HystrixFeign.Builder used to construct the components
• Client – LoadBalancerFeignClient or default Feign client

@FeignClient(value = "jplaceholder",
  url = "https://jsonplaceholder.typicode.com/",
  configuration = MyClientConfiguration.class)

Eg customeize client - okClient

@Configuration
public class MyClientConfiguration {

    @Bean
    public OkHttpClient client() {
        return new OkHttpClient();
    }
}

also support config using properties

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

Interceptor

The interceptors can perform a variety of implicit tasks, from authentication to logging, for every HTTP request/response.

Eg

@Bean
public RequestInterceptor requestInterceptor() {
  return requestTemplate -> {
      requestTemplate.header("user", username);
      requestTemplate.header("password", password);
      requestTemplate.header("Accept", ContentType.APPLICATION_JSON.getMimeType());
  };
}

feign:
  client:
    config:
      default:
        requestInterceptors:
          {intercetpr calss}

hystrix support

Fallback.

• feign.hystrix.enabled=true

eg

@Component
public class JSONPlaceHolderFallback implements JSONPlaceHolderClient {

    @Override
    public List<Post> getPosts() {
        return Collections.emptyList();
    }

    @Override
    public Post getPostById(Long postId) {
        return null;
    }
}

@FeignClient(value = "jplaceholder",
  url = "https://jsonplaceholder.typicode.com/",
  fallback = JSONPlaceHolderFallback.class)
public interface JSONPlaceHolderClient {
    // APIs
}

https://www.baeldung.com/spring-cloud-openfeign