Lightweight REST Clients with Feign (Feign is fine)
Problem: Seperate REST Clients for Every Direct Communication
Within the Microservices/REST “universe”, a separate client is required for each direct communication between services. Writing these clients is simple, but not very exciting, and leads to boilerplate code.
Solution: Minimal Code Usage in Spring Thanks to Feign
The declarative REST-client Feign allows in Spring applications to perform this task with minimal code usage.
Advantages / Features:
- freely configurable encoders/decoders (JSON, XML, ...), loggers, error handlers and interceptors (e.g. for OAuth)
- compatible with JAX-RS annotations, Spring Cloud, Hystrix, Spring MVC annotations, Spring Web HttpMessageConverter
- allows load balancing (with Ribbon and Eureka)
- more complex clients can be realized with the Feign Builder API
Example for a Feign Client
@FeignClient(name = "coffeeMachineClient", configuration = Config.class, url = "${myUrl}")
public interface ICoffeeMachineCient {
@RequestMapping(method = POST, path = "/coffees")
CupOfCoffeeDTO createCoffee(@RequestHeader("userId") Id uId, CupOfCoffeeDTO request);
@RequestMapping(method = GET, path = "/coffees")
List<CupOfCoffeeDTO> getCoffees();
@RequestMapping(method = GET, path = "/coffees/{id}")
CupOfCoffeeDTO getCoffeeById(@RequestParam("id") String coffeeId);
@RequestMapping(method = PUT, path = "/coffees/{id}")
CupOfCoffeeDTO updateCoffee(@RequestParam("id") String id, CupOfCoffeeDTO request);
@RequestMapping(method = DELETE, path = "/coffees/{id}")
void deleteCoffee(@RequestParam("id") String id); //who would do this?
}→ less than 15 lines of code for a complete CRUD client.Using Feign particularly pays off in case of many different requests having to be issued against a particular server.
Caution: Feign clients can’t handle binary data (e.g. file upload/download), but only text-based interfaces!
