Declarative HTTP Interface Clients (Boot 4)

Define a remote API as an interface with @HttpExchange methods. Boot 4 registers the proxy with @ImportHttpServices, so do not create a manual factory for every client.

Define and register the interface

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

    @PostExchange
    OrderDto create(@RequestBody CreateOrderRequest request);
}

@SpringBootApplication
@ImportHttpServices(group = "orders", basePackages = "com.example.client.orders")
public class Application { }

Inject OrderApiClient like any other bean. The interface needs no @Component and no implementation class.

Configure groups and transport

spring:
  http:
    clients:
      connect-timeout: 2s
      read-timeout: 5s
    serviceclient:
      orders:
        base-url: https://orders.internal.example.com
        read-timeout: 10s

spring.http.clients.* contains global transport defaults. spring.http.serviceclient.<group>.* contains per-group settings, and the group name must match @ImportHttpServices.

The default client type is blocking RestClient. Select HttpServiceGroup.ClientType.WEB_CLIENT for interfaces returning Mono or Flux, and include the WebClient starter. Group configurers apply to a group, not one interface.

Manual HttpServiceProxyFactory wiring remains valid for one-off clients, but it is the Boot 3 pattern and should not be the default in Boot 4.

Gotchas

• Agent creates a HttpServiceProxyFactory bean for every client - use @ImportHttpServices and groups.
• Agent adds @Component or an implementation to the interface - generated proxies need neither.
• Agent uses spring.http.client.* - global defaults are under spring.http.clients.*; group settings use serviceclient.
• Agent hard-codes a host in @HttpExchange and sets a group base URL - keep the host in configuration.
• Agent returns Mono or Flux with the default client - select WEB_CLIENT explicitly.
• Agent assumes a group configurer customizes one interface - configure the group or separate the group.