Allow customization of the ProxyFactory in HttpServiceProxyFactory used to create HTTP service proxies

[dungdm93]

The Spring Data project provides support for RepositoryProxyPostProcessor, which allows customization of the underlying ProxyFactory (e.g, registering additional interceptors) prior to proxy bean creation.

In contrast, HttpServiceProxyFactory, which is responsible for creating client proxies from HTTP service interfaces annotated with @HttpExchange, currently does not offer a straightforward extension point for registering interceptors (e.g., for tracing or cross-cutting concerns).

Example usage of HttpServiceProxyFactory.ProxyFactoryCustomizer:

public class OpenTelemetryHttpServiceProxyFactoryCustomizer implements HttpServiceProxyFactory.ProxyFactoryCustomizer {
    private final SingletonSupplier<OpenTelemetry> openTelemetry;
    private final HttpServiceGroup group;

    public OpenTelemetryHttpServiceProxyFactoryCustomizer(SingletonSupplier<OpenTelemetry> openTelemetry, HttpServiceGroup group) {
        this.openTelemetry = openTelemetry;
        this.group = group;
    }

    @Override
    public void customize(ProxyFactory factory, Class<?> serviceType) {
        var interceptor = new OpenTelemetryMethodInterceptor(openTelemetry.obtain(), group);
        factory.addAdvice(0, interceptor);
    }
}

@Component
public class OpenTelemetryRestClientHttpServiceGroupConfigurer implements RestClientHttpServiceGroupConfigurer {
    private final SingletonSupplier<OpenTelemetry> openTelemetry;

    public OpenTelemetryRestClientHttpServiceGroupConfigurer(SingletonSupplier<OpenTelemetry> openTelemetry) {
        this.openTelemetry = openTelemetry;
    }

    @Override
    public void configureGroups(Groups<RestClient.Builder> groups) {
        groups.forEachProxyFactory(this::configureProxyFactory);
    }

    private void configureProxyFactory(HttpServiceGroup group, HttpServiceProxyFactory.Builder builder) {
        var customizer = new OpenTelemetryHttpServiceProxyFactoryCustomizer(openTelemetry, group);
        builder.proxyCustomizer(customizer);
    }
}

[rstoyanchev]

Thanks for the suggestion. The request makes sense, however I would update the implementation a bit as suggested below. Having at least one test would also be a good idea.

Please, let me know if you will make those updates.

[dungdm93]

@rstoyanchev I update PR as your suggestion, could you please take a look.

[rstoyanchev]

Thanks @dungdm93.