Description When using @HttpExchange clients with a custom RestClient built from a RestTemplate, setting RestTemplateBuilder.rootUri() has no effect on methods that take an URI as a parameter:

``` @Configuration open class Configuration {

  @Bean
  open fun testClient(): TestClient {
      val restTemplateBuilder = RestTemplateBuilder()
          .rootUri("https://google.com")
          .additionalInterceptors(TestSpringInterceptor())

      val restTemplate = restTemplateBuilder.build()

      val restClient = RestClient.create(restTemplate)
      val clientAdapter = RestClientAdapter.create(restClient)
      return HttpServiceProxyFactory
          .builderFor(clientAdapter)
          .build()
          .createClient(TestClient::class.java)
  }

}

@HttpExchange interface TestClient {

  @GetExchange(url = "/apis")
  fun annotationUrl()

  @GetExchange
  fun parameterUrl(uri: URI)

}

class TestSpringInterceptor : ClientHttpRequestInterceptor { override fun intercept(request: HttpRequest, body: ByteArray, execution: ClientHttpRequestExecution): ClientHttpResponse { println("Request URI: ${request.uri}") return execution.execute(request, body) } }

@SpringBootApplication open class App

fun main(args: Array) { val ctx = runApplication(*args) val testClient = ctx.getBean(TestClient::class.java) testClient.annotationUrl() // prints "Request URI: https://google.com/apis" testClient.parameterUrl(URI.create("/apis")) // prints "Request URI: /apis" }


Setting the base URL through `RestClient.builder().baseUrl()` works but you lose the benefits of customizing the `RestTemplate`. From my debugging, the possible reason for that behaviour is because `DefaultRestClient` has the following code:

    public RestClient.RequestBodySpec uri(URI uri) {
        if (uri.isAbsolute()) {
            this.uri = uri;
        } else {
            URI baseUri = DefaultRestClient.this.uriBuilderFactory.expand("", new Object[0]);
            this.uri = baseUri.resolve(uri);
        }

        return this;
    }

When using `RestTemplateBuilder.rootUri()` the `uriBuilderFactory` here is an instance of `RootUriBuilderFactory`, which in turn fully ignores the base url during expansion:

public URI expand(String uriTemplate, Object... uriVariables) {
    return this.handler.expand(this.apply(uriTemplate), uriVariables);
}

String apply(String uriTemplate) {
    if (StringUtils.startsWithIgnoreCase(uriTemplate, "/")) {    // empty uriTemplate is passed so rootUri does not apply
        String var10000 = this.getRootUri();
        return var10000 + uriTemplate;
    } else {
        return uriTemplate;
    }
}

`` The different behaviour between passing the URI as a param and setting the URL through the annotation is due toUrlArgumentResolverusingRequestValues.setUri()when URI is passed as an argument andHttpRequestValuesInitializerusingRequestValues.setUriTemplate()when URL is set through@HttpExchange`.