http-interface-clients ยท diff
git:20260807.5f992d7 to git:20261102.3d7b68e
35 added, 0 removed. Audit A to A.
---
name: http-interface-clients
description: >
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.
---
# 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.
+ ## Transport failure contract
+
+ Define an adapter policy before adding retry annotations. The companion
+ [CatalogHttpClient](templates/CatalogHttpClient.java) implements the
+ `CatalogRetryService.CatalogTransport` port from the resilience-retry skill and uses
+ explicit JDK connect/read timeouts. It is a small imperative adapter example, not a reason
+ to replace an existing HTTP interface or Boot-managed client.
+
+ | Failure | Example policy for an idempotent read |
+ | --- | --- |
+ | 401/403, malformed request, missing resource | Surface the domain-appropriate error; no blind retry |
+ | 502/503/504, connect/read timeout | Translate to the bounded retry policy |
+ | 429 with Retry-After | Schedule only within the caller's budget; not implemented by this example |
+ | Cancellation or interruption | Propagate immediately, preserving interruption |
+ | Invalid response body or TLS/certificate error | Diagnose; do not repeatedly retry by default |
+
+ For POST/payment calls, preserve the same idempotency key and request bytes across retries;
+ a timeout does not prove the server did nothing. Never forward inbound Authorization to an
+ arbitrary destination: configure credentials per trusted service. Do not allow an end user
+ to choose the base URL. Avoid logging tokens or raw upstream error bodies.
+
+ Test the real client adapter against a stub HTTP server, including permanent status codes,
+ transient-then-success responses, malformed bodies, delayed responses and cancellation.
+ Keep connect, read, pool-acquisition and total deadlines distinct. When using WebClient,
+ apply a total timeout around the whole retry sequence and avoid blocking the event loop.
+
+ See [Spring REST clients](https://docs.spring.io/spring-framework/reference/integration/rest-clients.html).
+
+ ## Verification scope
+
+ The repository fixture targets Boot 3.5.16 with Java 17/21 and checks
+ the imperative catalog adapter against a local HTTP server; not every declarative group-registration option. Check the
+ [coverage matrix](https://github.com/rrezartprebreza/spring-boot-skills/blob/main/verification/MATRIX.md)
+ before treating another minor version or an illustrative snippet as verified.
+
## 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.