Explain the lifecycle of a request handled through an HTTP Interface client (@HttpExchange) in Spring 7?

An HTTP Interface client is a plain interface annotated with @HttpExchange-family annotations; at startup, HttpServiceProxyFactory generates a JDK dynamic proxy implementing that interface, so the application never writes an implementation by hand.

sequenceDiagram
    participant App as Application code
    participant Proxy as Generated proxy
    participant Adapter as RestClientAdapter/WebClientAdapter
    participant Client as RestClient/WebClient
    App->>Proxy: call interface method
    Proxy->>Proxy: build HttpRequestValues from args/annotations
    Proxy->>Adapter: delegate exchange
    Adapter->>Client: perform HTTP call
    Client-->>Adapter: HTTP response
    Adapter-->>Proxy: raw response
    Proxy-->>App: converted return value

When application code calls an interface method, the proxy's invocation handler builds an HttpRequestValues object from the method's arguments and annotations - path variables, query params, headers, request body - and, if the method declares a version attribute, attaches that to the request through the configured API-versioning strategy. It then delegates to an adapter (RestClientAdapter wrapping a RestClient for synchronous use, or WebClientAdapter wrapping a WebClient for reactive use), which performs the actual HTTP exchange. The adapter's underlying client applies whatever interceptors, error handling, and observation/tracing instrumentation it's configured with, receives the response, and the proxy converts the response body into the method's declared return type via message converters before handing it back - synchronously as a plain object if backed by RestClient, or wrapped in a Mono/Flux if the interface method itself is declared reactively.

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