Making REST Communication Easy with Feign Clients

In this example, we shall show you how to develop a simple Spring Boot Application with a Feign client for consuming a Weather REST service.

Spring Boot is a Java-based framework, which simplifies the building of web and enterprise applications. Spring Boot has an embedded Tomcat, provides ‘starter’ dependencies and no requires the configuration of XMLs.

Feign is a declarative framework developed by Netflix for implementing REST API clients. Feign allows building REST clients declaring and annotating an interface, the actual implementation is provisioned at runtime.

1. Project Environment

This example will be implemented using the following tools:

1. JDK 1.8.81
2. IntelliJ 2018.2.2
3. Spring Boot 2.0.4
4. Gradle 4.10
5. Spring Cloud Finchley.SR1

With this information, let’s start!

2. Create a Spring Boot Application

Click on File -> New -> Project

Select Spring Initializr and choose the proper JDK version.

Add a Group and Artifact name. Select Gradle Project and enter a version for your project.

In the next window select the options:

• Core -> DevTools
• Web -> Web
• Cloud -> Cloud Bootstrap

Choose a location for the project and clic on Finish button.

And Voila! You have a Spring Boot Application.

3. Create a Controller and Start the Application

Create one class named FeignController. Annotate the Java Class as a Controller and implement a GET method that returns a ResponseEntity with dummy data. After, I am going to complete the map with real information.

package com.example.feign.controller;

@RestController
public class FeignController {

    private final IWeatherClient weatherClient;

    @Autowired
    public FeignController(IWeatherClient weatherClient) {
        this.weatherClient = weatherClient;
    }

    @GetMapping(path = "/weather")
    ResponseEntity<Map> getWeather() {
        return ResponseEntity.ok(weatherClient.getWeather().getBody());
    }
}

Edit the file application.properties with the port for deploying the application.

server.port=9090

Finally, run and test the first version of the application.

4. Feign Client Implementation

Edit build.gradle file and include the next dependencies:

compile('org.springframework.boot:spring-boot-starter-web-services')
compile('org.springframework.cloud:spring-cloud-starter-openfeign')
compile('org.springframework.cloud:spring-cloud-starter-config')

Remember run the build Gradle task.

Create one package and one interface. It will be our Feign Client. I have named it IWeatherClient

Annotate the interface as a FeignClient and add one method for getting the weather. The annotation @FeignClient requires that you include the name and URL of the service. In this case, I have chosen datalike name and I have used a property for the URL.

package com.example.feign.feign;

@FeignClient(name = "data", url = "${feign.client.url}")
public interface IWeatherClient {

    @RequestMapping(method = RequestMethod.GET)
    ResponseEntity<Map> getWeather();

}

Add one implementation for the interface. It will be the fallback if something goes wrong invocating the service. In this case, I don’t have a fallback, so I am returning null.

package com.example.feign.feign.imp;

@Component
public class WeatherFallback implements IWeatherClient {

    @Override
    public ResponseEntity



<map> getWeather() {
        return null;
    }

}
</map>

Annotate the main class to enable Feign Clients. The annotation @EnableFeignClients requires that you include the base packages.

package com.example.feign;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.cloud.openfeign.EnableFeignClients;

@SpringBootApplication
@EnableFeignClients(basePackages = {"com.example.feign.feign",
        "com.example.feign.controller"})
public class FeignApplication {

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

Finally, use the feign client in the controller and run again the application.

5. Conclusion

This entry explained how to build a declarative HTTP client using Feign to consume a Weather API. The goal of Feign is reducing the complexity of binding a denominator uniformly with HTTP APIS regardless of restfulness.

6. Download the Project