Feign 이란

Feign 이란 Netflix 에서 개발된 오픈소스이며 선언적 방식으로 REST 기반 호출을 추상화해서 제공한다. 즉, interface 와 annotaion 만으로 간편하게 HTTP API Client 를 구현할 수 있으며 RestTemplate 을 만들 필요없이 사용할 수 있어 코드의 복잡성이 낮아진다.

샘플코드는 하기 링크로 확인

샘플코드

사용법

Dependency

maven [pom.xml]
```

org.springframework.cloud spring-cloud-dependencies ${spring-cloud.version} pom import

…

org.springframework.cloud spring-cloud-starter-openfeign

- gradle      
[build.gradle]   

… // https://spring.io/projects/spring-cloud 에서 Spring Boot 버전에 맞게 세팅한다. (해당 포스팅은 Spring Boot 2.2.2.RELEASE 로 진행) ext { set(‘springCloudVersion’, “Hoxton.SR3”) }

dependencyManagement { imports { mavenBom “org.springframework.cloud:spring-cloud-dependencies:${springCloudVersion}” } }

dependencies { … implementation ‘org.springframework.cloud:spring-cloud-starter-openfeign’ }

## SpringApplication.java 에 @EnableFeignClients 을 선언
[ApiApplication.java]    

@EnableFeignClients @SpringBootApplication … public class ApiApplication {

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

}

## Feign 사용
먼저 패키지를 생성하자. 패키지는 ApiApplication.java 와 같은 레벨인 Root Package 에 존재하여야 하며, 그렇지 않으면 basePackages 또는 basePackageClasses 를 지정해야 한다. feign 이라는 패키지를 생성하고 그 안에 user 패키지 생성 후 또 그 안에 FeignUserClient.java 라는 클래스를 생성하자. (혹시 수동으로 구현체를 생성하고 싶으면 [수동 구현체 생성](https://cloud.spring.io/spring-cloud-netflix/multi/multi_spring-cloud-feign.html#_creating_feign_clients_manually) 링크를 참고)     
[../feign/user/FeignUserClient.java]     

package com.example.bkjeon.base.feign.user;

import java.util.List;

import org.springframework.cloud.openfeign.FeignClient; import org.springframework.cloud.openfeign.SpringQueryMap; import org.springframework.web.bind.annotation.GetMapping; import org.springframework.web.bind.annotation.PathVariable; import org.springframework.web.bind.annotation.RequestParam;

import com.example.bkjeon.base.feign.user.model.FeignUserRequest;

@FeignClient( configuration = FeignUserClientConfig.class, fallbackFactory = FeignUserClientFallback.class, name = “example”, url = “${external-api.url}” ) public interface FeignUserClient {

@GetMapping("users")
List<FeignUser> getUserList(@SpringQueryMap FeignUserRequest feignUserRequest);

@GetMapping("users/{userId}")
FeignUser getUser(@PathVariable("userId") Integer userId, @RequestParam("testCode") String testCode);

}

     
API 를 호출할 도메인 및 토큰 입력
[application.yml]   

…

external: api: user: url: https://jsonplaceholder.typicode.com token: eyJhbGciOiJIUzUxMiJ9.eyJzdWIiOiJ7XCJwb3NpdERlcHRJZFwiOjMsXCJkbW5DZFwiOlwiRUxUXCIsXCJhcGlrZXlJZFwiOlwiRUxUXzE1NTY1MjM

결과값을 받을 클래스를 생성한다.     
[../feign/user/entity/FeignUser.java]  

package com.example.bkjeon.base.feign.user.entity;

import lombok.Getter; import lombok.NoArgsConstructor;

@Getter @NoArgsConstructor public class FeignUser {

private Integer id;
private String name;
private String username;
private String email;
private Address address;
private String phone;
private String website;
private Company company;

@Getter
public static class Address {
    private String street;
    private String suite;
    private String city;
    private String zipcode;
    private Geo geo;

    @Getter
    public static class Geo {
        private String lat;
        private String lng;
    }
}

@Getter
public static class Company {
    private String name;
    private String catchPhrase;
    private String bs;
}

}

     
요청시 필요한 파라미터 클래스를 생성한다.   
[../feign/user/FeignUserRequest.java]

package com.example.bkjeon.base.feign.user.model;

import lombok.Builder; import lombok.ToString;

@ToString public class FeignUserRequest {

private String testCode;

@Builder
public FeignUserRequest(String testCode) {
	  this.testCode = testCode;
}

}

             
실패할 경우 예외처리할 클래스를 생성한다.   
[../feign/user/FeignUserClientFallback.java]    

package com.example.bkjeon.base.feign.user;

import java.util.List;

import org.springframework.stereotype.Component;

import com.example.bkjeon.base.feign.user.model.FeignUserRequest;

import feign.hystrix.FallbackFactory; import lombok.extern.slf4j.Slf4j;

/**

Exception */ @Component @Slf4j public class FeignUserClientFallback implements FallbackFactory {

@Override public FeignUserClient create(Throwable throwable) { return new FeignUserClient() { @Override public List getUserList(FeignUserRequest feignUserRequest) { log.error("param: {}, error ==> {}", feignUserRequest.toString(), throwable.toString()); return null; }
```
     @Override
     public FeignUser getUser(Integer userId, String testCode) {
         log.error("param: userId ==> {}, testCode ==> {}, error ==> {}", userId, testCode, throwable.toString());
         return new FeignUser();
     }
 };  }
```

}

         
API 요청시 헤더에 세팅할 인터셉터를 구현한다.     
[../feign/user/FeignClientInterceptor.java]    

package com.example.bkjeon.base.feign.user;

import com.google.common.base.Preconditions;

import feign.RequestInterceptor; import feign.RequestTemplate;

/**

Header Setting Interceptor */ public class FeignClientInterceptor implements RequestInterceptor {

private String apiToken;

public FeignClientInterceptor(String apiToken) { Preconditions.checkNotNull(apiToken, “Api Token Should Not Be Null”); this.apiToken = apiToken; }

@Override public void apply(RequestTemplate template) { template.header(“Authorization”, “Bearer “ + apiToken); template.header(“Content-Type”, “application/json”); }

}

             
Header 값 등 세팅할 Configuration 을 생성      
[../feign/user/FeignUserClientConfig.java]

package com.example.bkjeon.base.feign.user;

import org.springframework.beans.factory.annotation.Value; import org.springframework.context.annotation.Bean;

import feign.RequestInterceptor;

/**

Feign Configuration */ public class FeignUserClientConfig {

@Bean public RequestInterceptor requestHeader(@Value(“${external-api.token}”) String apiToken) { return new FeignUserClientInterceptor(apiToken); }

}

        
## Feign 을 사용할 Controller 생성
[FeignExampleController.java]    

package com.example.bkjeon.base.services.api.v1.feign;

import java.util.List;

import org.springframework.web.bind.annotation.GetMapping; import org.springframework.web.bind.annotation.PathVariable; import org.springframework.web.bind.annotation.RequestMapping; import org.springframework.web.bind.annotation.RestController;

import com.example.bkjeon.base.feign.user.FeignUserClient; import com.example.bkjeon.base.feign.user.entity.FeignUser; import com.example.bkjeon.base.feign.user.model.FeignUserRequest;

import io.swagger.annotations.ApiOperation; import lombok.RequiredArgsConstructor;

@RestController @RequiredArgsConstructor @RequestMapping(“v1/feign”) public class FeignExampleController {

private final FeignUserClient feignUserClient;

@ApiOperation("Feign 을 통한 User 목록 조회")
@GetMapping("users")
public List<FeignUser> getUserList() {
    FeignUserRequest feignUserRequest = FeignUserRequest.builder().testCode("bkjeon").build();
    return feignUserClient.getUserList(feignUserRequest);
}

@ApiOperation("Feign 을 통한 User 상세 조회")
@GetMapping("users/{userId}")
public FeignUser getUser(@PathVariable Integer userId) {
    return feignUserClient.getUser(userId, "bkjeon");
}

}


## 결과확인

http://localhost:9090/api/v1/feign/users 또는 http://localhost:9090/api/v1/feign/users/1 ```

Feign 패키지 구조

springboot-feign-1

SpringBoot 에서 FeignClient 를 사용하여 Rest API 를 간편하게 사용하자

2022-12-17-java-springboot-feignclient.md

Feign 이란

샘플코드는 하기 링크로 확인

사용법

Dependency

Feign 패키지 구조