Mastering Spring Boot 3’s @HttpExchange for Declarative HTTP Calls

1. Origin

Spring Boot 3, released at the end of last year, introduces the @HttpExchange annotation, providing a native way to declare HTTP calls without relying on third‑party libraries such as OpenFeign.

2. Usage Example – Server

First, create a simple Spring Boot project named server that exposes a test endpoint:

@RestController
public class HelloController {

    @GetMapping("/server/hello")
    public String hello(String name) {
        return "hello " + name;
    }
}

3. Usage Example – Client

Next, create a second project called client. In addition to the standard web starter, add the reactive-web starter because @HttpExchange is built on top of WebClient:

Define a declarative interface for the remote call:

@HttpExchange("/server")
public interface ToDoService {
    @GetExchange("/hello")
    String hello(@RequestParam String name);
}

The annotations map directly to familiar Spring MVC ones: @HttpExchange works like @RequestMapping, @GetExchange like @GetMapping, and there are equivalents such as @PostExchange, @DeleteExchange, @PatchExchange, and @PutExchange. Parameters must be annotated with @RequestParam, similar to OpenFeign.

4. Configuration

To enable the declarative client, configure a WebClient bean and a proxy factory:

@Configuration
public class WebConfig {
    @Bean
    WebClient webClient() {
        return WebClient.builder()
            .baseUrl("http://localhost:8080")
            .build();
    }

    @Bean
    ToDoService toDoService() {
        HttpServiceProxyFactory factory = HttpServiceProxyFactory.builder(
            WebClientAdapter.forClient(webClient()))
            .build();
        return factory.createClient(ToDoService.class);
    }
}

The first bean supplies the underlying WebClient, which defines the base URL and can be used to customize headers. The second bean creates a proxy implementation of the ToDoService interface using HttpServiceProxyFactory.

5. Consuming the Service

With the configuration in place, the client can inject ToDoService and call the remote method directly:

@SpringBootTest
class ClientApplicationTests {

    @Autowired
    ToDoService toDoService;

    @Test
    void contextLoads() {
        String hello = toDoService.hello("javaboy");
        System.out.println("hello = " + hello);
    }
}

This test demonstrates a straightforward, type‑safe HTTP call without any OpenFeign code.

6. Conclusion

Spring Boot 3’s @HttpExchange offers a clean, declarative alternative for inter‑service communication, leveraging the reactive WebClient stack and eliminating the need for external Feign dependencies.