Feign Client in Spring Boot

Feign Client in Spring Boot

Feign is a declarative REST client in Spring Cloud that makes writing web service clients easier. Instead of writing boilerplate RestTemplate or WebClient code, you define an interface and annotate it — Spring generates the implementation for you at runtime.

Here’s a step-by-step example of using Feign Client in Spring Boot:

1. Add dependencies

In your pom.xml (Maven):

<dependency>
    <groupId>org.springframework.cloud</groupId>
    <artifactId>spring-cloud-starter-openfeign</artifactId>
</dependency>

<dependencyManagement>
    <dependencies>
        <dependency>
            <groupId>org.springframework.cloud</groupId>
            <artifactId>spring-cloud-dependencies</artifactId>
            <version>2023.0.1</version> <!-- check latest version -->
            <type>pom</type>
            <scope>import</scope>
        </dependency>
    </dependencies>
</dependencyManagement>

For Gradle:

implementation 'org.springframework.cloud:spring-cloud-starter-openfeign'

dependencyManagement {
    imports {
        mavenBom "org.springframework.cloud:spring-cloud-dependencies:2023.0.1"
    }
}

2. Enable Feign Clients

In your Spring Boot main application class:

@SpringBootApplication
@EnableFeignClients
public class FeignDemoApplication {
    public static void main(String[] args) {
        SpringApplication.run(FeignDemoApplication.class, args);
    }
}

3. Create a Feign Client Interface

Suppose we want to call an external REST API (like JSONPlaceholder).

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

import java.util.List;

@FeignClient(name = "jsonPlaceholderClient", url = "https://jsonplaceholder.typicode.com")
public interface JsonPlaceholderClient {

    @GetMapping("/posts")
    List<Post> getPosts();

    @GetMapping("/posts/{id}")
    Post getPostById(@PathVariable("id") Long id);
}

4. Create a Model Class

public class Post {
    private Long userId;
    private Long id;
    private String title;
    private String body;

    // getters and setters
}

5. Use Feign Client in a Service

import org.springframework.stereotype.Service;
import java.util.List;

@Service
public class PostService {

    private final JsonPlaceholderClient jsonPlaceholderClient;

    public PostService(JsonPlaceholderClient jsonPlaceholderClient) {
        this.jsonPlaceholderClient = jsonPlaceholderClient;
    }

    public List<Post> getAllPosts() {
        return jsonPlaceholderClient.getPosts();
    }

    public Post getPostById(Long id) {
        return jsonPlaceholderClient.getPostById(id);
    }
}

6. Expose via Controller

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

import java.util.List;

@RestController
public class PostController {

    private final PostService postService;

    public PostController(PostService postService) {
        this.postService = postService;
    }

    @GetMapping("/posts")
    public List<Post> getPosts() {
        return postService.getAllPosts();
    }

    @GetMapping("/posts/{id}")
    public Post getPostById(@PathVariable Long id) {
        return postService.getPostById(id);
    }
}

7. Run and Test

Start the Spring Boot application and test:

  • http://localhost:8080/posts → returns list of posts
  • http://localhost:8080/posts/1 → returns single post

✨ That’s it — you now have a working Feign client in Spring Boot!

Do you want me to also show you how to add fallback handling (Resilience4j/Hystrix) for Feign in case the external API is down?

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