20 Feign Client Interview Questions and Answers

Feign Client is a popular Java library used for making HTTP requests. If you’re applying for a position that involves Java development, it’s likely that you’ll be asked questions about Feign Client during your interview. Knowing how to answer these questions can help you impress the hiring manager and improve your chances of getting the job. In this article, we discuss the most commonly asked Feign Client questions and provide example answers to help you prepare for your next interview.

Feign Client Interview Questions and Answers

Here are 20 commonly asked Feign Client interview questions and answers to prepare you for your interview:

1. What is Feign?

Feign is a Java library that makes it easy to create web service clients. It takes care of all the boilerplate code that comes with making web service calls, so you can focus on your application logic. Feign also supports load balancing and circuit breaker patterns out of the box.

2. Can you explain how a Feign client works?

A Feign client is a Java library that allows you to create web service clients in a declarative way. With Feign, you can write Java code that makes HTTP requests to web services without having to deal with the low-level details of the underlying HTTP protocol. Feign clients are typically used in conjunction with a service discovery tool like Eureka, which allows them to dynamically discover and connect to services at runtime.

3. Is it possible to configure multiple decoders in Feign? If yes, then how?

Yes, it is possible to configure multiple decoders in Feign. You can do this by specifying the decoders you want to use in the @FeignClient annotation, like so:

@FeignClient(name = “my-feign-client”, url = “http://example.com”, decoders = { MyDecoder1.class, MyDecoder2.class })
public interface MyFeignClient {
// …
}

4. How do you enable decoding GZIP responses with Feign?

You can enable decoding GZIP responses with Feign by setting the feign.decodeGzip property to true.

5. Is it possible to send requests asynchronously using Feign clients? If yes, then how?

Yes, it is possible to send requests asynchronously using Feign clients. This can be done by using the @Async annotation on the methods that you want to execute asynchronously.

6. What are the different ways of making HTTP Requests using Feign clients?

There are four different ways of making HTTP Requests using Feign clients:

1. Using the @RequestLine annotation
2. Using the @RequestMapping annotation
3. Using the @RequestParam annotation
4. Using the @PathVariable annotation

7. What happens when you invoke an application that doesn’t exist but has been registered with Eureka?

When you invoke an application that doesn’t exist but has been registered with Eureka, the Feign client will automatically route the request to the appropriate application. This is because the Feign client uses Eureka to lookup the application’s URL and then forwards the request to that URL.

8. What’s the difference between @FeignClient and Spring RestTemplate?

@FeignClient is a higher level abstraction over the RestTemplate. It allows you to declaratively create REST clients. With the RestTemplate, you have to do everything yourself.

9. When should you use @RequestMapping instead of @GetMapping or @PostMapping annotations for handling HTTP requests?

@RequestMapping is a more general annotation that can be used for handling any type of HTTP request, while @GetMapping and @PostMapping are more specific and should only be used for handling GET and POST requests, respectively. If you are unsure which annotation to use, @RequestMapping is probably the best choice.

10. What does the @EnableFeignClients annotation mean?

The @EnableFeignClients annotation is used to enable Feign Client in a Spring Boot application. This annotation will scan the classpath for any interfaces that are annotated with @FeignClient and create a proxy for them.

11. What happens if you don’t declare the required headers while invoking a method annotated with @Headers on a feign client?

If you don’t declare the required headers while invoking a method annotated with @Headers on a feign client, then the request will fail and an error will be thrown.

12. What are some common pitfalls developers run into when they start using Feign clients?

One common issue is that developers forget to add the @EnableFeignClients annotation to their main application class. Without this annotation, the Feign client will not be created and you will not be able to use it. Another common issue is that developers try to use Feign clients without first creating an interface for the client. The interface is necessary in order to tell the Feign client what methods to use and how to map the parameters.

13. What’s the significance of the fallback attribute on the @FeignClient annotation?

The fallback attribute is used to specify a fallback class that will be used if the Feign client is unable to connect to the server. This is useful for providing a backup in case of a server outage or other connection issue.

14. What is retryable behavior and why is it important?

Retryable behavior is the ability of a client to automatically retry a request in the event of a failure. This is important because it can help to ensure that a request is successful even if there is a temporary failure.

15. What is Ribbon and how does it work with Feign clients?

Ribbon is a load balancing library that works with Feign clients to provide intelligent and efficient routing of requests. Ribbon uses a number of algorithms to determine the best way to route a request, and it can also work with a number of different back-end services. This makes it an ideal solution for microservices architectures, where there are often many different services that need to be called in order to complete a request.

16. What is Hystrix and how does it work with Feign clients?

Hystrix is a library that helps to control the interactions between microservices, and it works with Feign clients by providing a fallback option in case of failure. If a Feign client is unable to connect to a service, Hystrix will step in and provide an alternate response. This helps to prevent errors from propagating throughout the system and keeps the system running smoothly.

17. What are the differences between Feign, Retrofit and JAX-RS 2.0 (Jersey)? Which one would you recommend and why?

There are a few key differences between Feign, Retrofit and JAX-RS 2.0 (Jersey). Feign is a library that allows you to create declarative web service clients in a concise, Java 8-friendly way. Retrofit is a library that allows you to access RESTful web services in a type-safe way. JAX-RS 2.0 (Jersey) is a standard for building RESTful web services in Java.

I would recommend Feign because it is the most concise and Java 8-friendly of the three options.

18. What are the advantages of using Feign over REST Template?

There are several advantages of using Feign over REST Template. First, Feign makes it easier to create web service clients. It does this by providing a declarative way to create interfaces that can be used to access web services. Second, Feign automatically encodes and decodes request and response objects, which makes it easier to work with data from web services. Finally, Feign provides built-in support for load balancing and circuit breaking, which can help improve the performance and resilience of web service clients.

19. What is the best way to deal with timeouts with Feign Clients?

The best way to deal with timeouts with Feign Clients is to use the @FeignClient annotation and specify a fallback class. This way, if the Feign Client times out, it will automatically fall back to the specified class.

20. What is your understanding of error decoding in context with Feign clients?

Error decoding is the process of taking an error response from a server and translating it into a format that can be understood by the client. This is important because it allows the client to know what went wrong and take appropriate action.