Leichtgewichtige REST-Clients mit Feign

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!
Lightweight REST Clients with Feign

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