Hystrix Circuit Breaker and Feign Error Handling

In this tutorial you will learn how to handle errors when using Hystrix Circuit breaker together with Feign client. To handle errors we will use Feign Hystrix FallbackFactory.

For step-by-step video beginner lessons that demonstrate how to do Feign error handling and also how to build Microservices with Spring Boot and Spring Cloud, have a look at this page: Spring Boot Microservices and Spring Cloud.

When working with Feign and Error Handling the following tutorials might also be helpful:

• Feign Client to Call Another Microservice,
• Feign Client HTTP Requests Logging,
• Using Hystrix Circuit Breaker with Feign,
• Feign Error Handling with ErrorDecoder

Sample Feign Client

Let’s assume we have the following Feign client which sends HTTP Get request to a /users/${id}/albums endpoint of Microservice which is registered with Eureka discovery service under the name albums-ws.

@FeignClient(name = "albums-ws")
public interface AlbumsServiceClient {

    @GetMapping("/users/${id}/albums")
    public List<AlbumResponseModel> getAlbums(@PathVariable String id);

}

To enable the above Feign client to use a Fallback class which is able to handle error messages, we will need to update the @FeignClient annotation with fallbackFactory. Here is how:

@FeignClient(name = "albums-ws", fallbackFactory = AlbumsFallbackFactory.class)

and the updated Feign client will now look this way:

@FeignClient(name = "albums-ws", fallbackFactory = AlbumsFallbackFactory.class)
public interface AlbumsServiceClient {

    @GetMapping("/users/${id}/albumss")
    public List<AlbumResponseModel> getAlbums(@PathVariable String id);

}

The AlbumsFallbackFactory.class used in Feign annotation will be created in the example below.

Implementing Feign Hystrix FallbackFactory

In the example above we have used fallbackFactory. Now we need to create a class which implements the FallbackFactory.

@Component
class AlbumsFallbackFactory implements FallbackFactory<AlbumsServiceClient> {

    @Override
    public AlbumsServiceClient create(Throwable cause) {
        return new AlbumsServiceClientFallback(cause);
    }
}

Note: Notice the use of @Component annotation above the class name which implements FallbackFactory.

Aldo notice that we now have access to a Throwable object which we can use to get details of an error message that took place. The above code example passes the error object to a new class which will be used to deal with it.

class AlbumsServiceClientFallback implements AlbumsServiceClient {

    Logger logger = LoggerFactory.getLogger(this.getClass());
    private final Throwable cause;

    public AlbumsServiceClientFallback(Throwable cause) {
        this.cause = cause;
    }

    @Override
    public List<AlbumResponseModel> getAlbums(String id) {
        if (cause instanceof FeignException && ((FeignException) cause).status() == 404) {
            logger.error("404 error took place when getAlbums was called with userId: "
                    + id +  ". Error message: "
                    + cause.getLocalizedMessage());
        } else {
            logger.error("Other error took place: " + cause.getLocalizedMessage());
        }

        return new ArrayList<>();
    }
}

I hope this very short tutorial was helpful to you. If you are interested to watch a video lesson that demonstrates how to use FallbackFactory to handle errors and also how to build Microservices with Spring cloud, then have a look at this page:  Spring Boot Microservices and Spring Cloud.

To learn such a large topic as Spring Cloud and Microservices it is good to learn from different sources. This is because there is no single book or a video course that covers all. If you learn from multiple sources, there will be something new you will learn from each. Have a look at the below list of video courses that teach Spring cloud and maybe one of them will cover topics that you need to learn.