# HTTP Interface Clients

> Use when calling external HTTP APIs from Spring Boot 3 / Spring Framework 6 with declarative HttpExchange interfaces. Covers manual proxy registration, RestClient versus WebClient, and timeout and error handling conventions.

- Skill: `rrezartprebreza/http-interface-clients` (Agent Skill, multi-file: 4 files)
- Install (CLI): `npx skillmds@latest add rrezartprebreza/http-interface-clients`
- Raw SKILL.md: https://api.skillmd.com/api/skills/rrezartprebreza/http-interface-clients/raw
- Safety review: pending
- Works with: Claude Code, Claude.ai, OpenAI Codex
- Category: Coding & Dev Tools
- Author: rrezartprebreza (https://skillmd.com/u/rrezartprebreza)
- Updated: 2026-09-17
- Page: https://skillmd.com/skills/rrezartprebreza/http-interface-clients

---


# Declarative HTTP Interface Clients (Boot 3)

Spring Framework 6 supports `@HttpExchange` interfaces, but Boot 3 does not provide Boot 4's
`@ImportHttpServices` group auto-registration. Build the client adapter explicitly.

```java
@HttpExchange("/orders")
interface OrderApiClient {
    @GetExchange("/{id}")
    OrderDto get(@PathVariable UUID id);
}

@Configuration
class ClientConfig {
    @Bean
    OrderApiClient orderApiClient(RestClient.Builder builder,
                                  @Value("${clients.orders.base-url}") String baseUrl) {
        RestClient client = builder.baseUrl(baseUrl).build();
        HttpServiceProxyFactory factory =
            HttpServiceProxyFactory.builderFor(RestClientAdapter.create(client)).build();
        return factory.createClient(OrderApiClient.class);
    }
}
```

Use `WebClientAdapter` for reactive interfaces returning `Mono` or `Flux`. Configure base URLs,
timeouts, authentication, and error translation in the client adapter layer rather than in
controllers or domain services. Prefer one factory/configurer per external service.

## Gotchas

- Agent uses `@ImportHttpServices` - that Boot 4 registration API is not available in Boot 3.
- Agent adds `@Component` or an implementation to the interface - register the generated proxy as a bean.
- Agent uses `RestClient` for `Mono` or `Flux` - use `WebClientAdapter` for reactive return types.
- Agent hard-codes remote hosts in annotations - keep URLs in configuration.
- Agent lets transport errors leak through the domain - translate them in the client adapter.
- Agent creates a new client per request - configure and reuse a singleton proxy.