Polishing reference docs for HTTP Service clients

See gh-34912

Author: rstoyanchev

framework-docs/modules/ROOT/pages/integration/rest-clients.adoc

@@ -3,10 +3,10 @@
 
 The Spring Framework provides the following choices for making calls to REST endpoints:
 
-* xref:integration/rest-clients.adoc#rest-restclient[`RestClient`] - synchronous client with a fluent API.
-* xref:integration/rest-clients.adoc#rest-webclient[`WebClient`] - non-blocking, reactive client with fluent API.
-* xref:integration/rest-clients.adoc#rest-resttemplate[`RestTemplate`] - synchronous client with template method API.
-* xref:integration/rest-clients.adoc#rest-http-interface[HTTP Interface] - annotated interface with generated, dynamic proxy implementation.
+* xref:integration/rest-clients.adoc#rest-restclient[`RestClient`] -- synchronous client with a fluent API
+* xref:integration/rest-clients.adoc#rest-webclient[`WebClient`] -- non-blocking, reactive client with fluent API
+* xref:integration/rest-clients.adoc#rest-resttemplate[`RestTemplate`] -- synchronous client with template method API
+* xref:integration/rest-clients.adoc#rest-http-interface[HTTP Interface Clients] -- annotated interface backed by generated proxy
 
 
 [[rest-restclient]]
@@ -857,15 +857,17 @@ It can be used to migrate from the latter to the former.
 
 
 [[rest-http-interface]]
-== HTTP Interface
+== HTTP Interface Clients
 
-The Spring Framework lets you define an HTTP service as a Java interface with
-`@HttpExchange` methods. You can pass such an interface to `HttpServiceProxyFactory`
-to create a proxy which performs requests through an HTTP client such as `RestClient`
-or `WebClient`. You can also implement the interface from an `@Controller` for server
-request handling.
+You can define an HTTP Service as a Java interface with `@HttpExchange` methods, and use
+`HttpServiceProxyFactory` to create a client proxy from it for remote access over HTTP via
+`RestClient`, `WebClient`, or `RestTemplate`. On the server side, an `@Controller` class
+can implement the same interface to handle requests with
+xref:web/webmvc/mvc-controller/ann-requestmapping.adoc#mvc-ann-httpexchange-annotation[@HttpExchange]
+controller methods.
 
-Start by creating the interface with `@HttpExchange` methods:
+
+First, create the Java interface:
 
 [source,java,indent=0,subs="verbatim,quotes"]
 ----
@@ -879,69 +881,64 @@ Start by creating the interface with `@HttpExchange` methods:
 	}
 ----
 
-Now you can create a proxy that performs requests when methods are called.
-
-For `RestClient`:
+Optionally, use `@HttpExchange` at the type level to declare common attributes for all methods:
 
 [source,java,indent=0,subs="verbatim,quotes"]
 ----
-	RestClient restClient = RestClient.builder().baseUrl("https://api.github.com/").build();
-	RestClientAdapter adapter = RestClientAdapter.create(restClient);
-	HttpServiceProxyFactory factory = HttpServiceProxyFactory.builderFor(adapter).build();
+	@HttpExchange(url = "/repos/{owner}/{repo}", accept = "application/vnd.github.v3+json")
+	public interface RepositoryService {
 
-	RepositoryService service = factory.createClient(RepositoryService.class);
-----
+		@GetExchange
+		Repository getRepository(@PathVariable String owner, @PathVariable String repo);
 
-For `WebClient`:
+		@PatchExchange(contentType = MediaType.APPLICATION_FORM_URLENCODED_VALUE)
+		void updateRepository(@PathVariable String owner, @PathVariable String repo,
+				@RequestParam String name, @RequestParam String description, @RequestParam String homepage);
 
-[source,java,indent=0,subs="verbatim,quotes"]
+	}
 ----
-	WebClient webClient = WebClient.builder().baseUrl("https://api.github.com/").build();
-	WebClientAdapter adapter = WebClientAdapter.create(webClient);
-	HttpServiceProxyFactory factory = HttpServiceProxyFactory.builderFor(adapter).build();
 
-	RepositoryService service = factory.createClient(RepositoryService.class);
-----
 
-For `RestTemplate`:
+Next, configure the client and create the `HttpServiceProxyFactory`:
 
 [source,java,indent=0,subs="verbatim,quotes"]
 ----
+	// Using RestClient...
+
+	RestClient restClient = RestClient.create("...");
+	RestClientAdapter adapter = RestClientAdapter.create(restClient);
+
+	// or WebClient...
+
+	WebClient webClient = WebClient.create("...");
+	WebClientAdapter adapter = WebClientAdapter.create(webClient);
+
+	// or RestTemplate...
+
 	RestTemplate restTemplate = new RestTemplate();
-	restTemplate.setUriTemplateHandler(new DefaultUriBuilderFactory("https://api.github.com/"));
 	RestTemplateAdapter adapter = RestTemplateAdapter.create(restTemplate);
-	HttpServiceProxyFactory factory = HttpServiceProxyFactory.builderFor(adapter).build();
 
-	RepositoryService service = factory.createClient(RepositoryService.class);
+	HttpServiceProxyFactory factory = HttpServiceProxyFactory.builderFor(adapter).build();
 ----
 
-`@HttpExchange` is supported at the type level where it applies to all methods:
+Now, you're ready to create client proxies:
 
 [source,java,indent=0,subs="verbatim,quotes"]
 ----
-	@HttpExchange(url = "/repos/{owner}/{repo}", accept = "application/vnd.github.v3+json")
-	public interface RepositoryService {
-
-		@GetExchange
-		Repository getRepository(@PathVariable String owner, @PathVariable String repo);
-
-		@PatchExchange(contentType = MediaType.APPLICATION_FORM_URLENCODED_VALUE)
-		void updateRepository(@PathVariable String owner, @PathVariable String repo,
-				@RequestParam String name, @RequestParam String description, @RequestParam String homepage);
-
-	}
+	RepositoryService service = factory.createClient(RepositoryService.class);
+	// Use service methods for remote calls...
 ----
 
 
+
 [[rest-http-interface-method-parameters]]
 === Method Parameters
 
-Annotated, HTTP exchange methods support flexible method signatures with the following
-method parameters:
+`@HttpExchange` methods support flexible method signatures with the following inputs:
 
 [cols="1,2", options="header"]
 |===
-| Method argument | Description
+| Method parameter | Description
 
 | `URI`
 | Dynamically set the URL for the request, overriding the annotation's `url` attribute.
@@ -1005,26 +1002,26 @@ parameter annotation) is set to `false`, or the parameter is marked optional as
 
 
 [[rest-http-interface.custom-resolver]]
-=== Custom argument resolver
+=== Custom Arguments
 
-For more complex cases, HTTP interfaces do not support `RequestEntity` types as method parameters.
-This would take over the entire HTTP request and not improve the semantics of the interface.
-Instead of adding many method parameters, developers can combine them into a custom type
-and configure a dedicated `HttpServiceArgumentResolver` implementation.
-
-In the following HTTP interface, we are using a custom `Search` type as a parameter:
+You can configure a custom `HttpServiceArgumentResolver`. The example interface below
+uses a custom `Search` method parameter type:
 
 include-code::./CustomHttpServiceArgumentResolver[tag=httpinterface,indent=0]
 
-We can implement our own `HttpServiceArgumentResolver` that supports our custom `Search` type
-and writes its data in the outgoing HTTP request.
+A custom argument resolver could be implemented like this:
 
 include-code::./CustomHttpServiceArgumentResolver[tag=argumentresolver,indent=0]
 
-Finally, we can use this argument resolver during the setup and use our HTTP interface.
+To configure the custom argument resolver:
 
 include-code::./CustomHttpServiceArgumentResolver[tag=usage,indent=0]
 
+TIP: By default, `RequestEntity` is not supported as a method parameter, instead encouraging
+the use of more fine-grained method parameters for individual parts of the request.
+
+
+
 [[rest-http-interface-return-values]]
 === Return Values
 
@@ -1101,61 +1098,35 @@ underlying HTTP client, which operates at a lower level and provides more contro
 [[rest-http-interface-exceptions]]
 === Error Handling
 
-To customize error response handling, you need to configure the underlying HTTP client.
-
-For `RestClient`:
-
-By default, `RestClient` raises `RestClientException` for 4xx and 5xx HTTP status codes.
-To customize this, register a response status handler that applies to all responses
-performed through the client:
+To customize error handling for HTTP Service client proxies, you can configure the
+underlying client as needed. By default, clients raise an exception for 4xx and 5xx HTTP
+status codes. To customize this, register a response status handler that applies to all
+responses performed through the client as follows:
 
 [source,java,indent=0,subs="verbatim,quotes"]
 ----
+	// For RestClient
 	RestClient restClient = RestClient.builder()
 			.defaultStatusHandler(HttpStatusCode::isError, (request, response) -> ...)
 			.build();
-
 	RestClientAdapter adapter = RestClientAdapter.create(restClient);
-	HttpServiceProxyFactory factory = HttpServiceProxyFactory.builderFor(adapter).build();
-----
-
-For more details and options, such as suppressing error status codes, see the Javadoc of
-`defaultStatusHandler` in `RestClient.Builder`.
-
-For `WebClient`:
-
-By default, `WebClient` raises `WebClientResponseException` for 4xx and 5xx HTTP status codes.
-To customize this, register a response status handler that applies to all responses
-performed through the client:
 
-[source,java,indent=0,subs="verbatim,quotes"]
-----
+	// or for WebClient...
 	WebClient webClient = WebClient.builder()
 			.defaultStatusHandler(HttpStatusCode::isError, resp -> ...)
 			.build();
-
 	WebClientAdapter adapter = WebClientAdapter.create(webClient);
-	HttpServiceProxyFactory factory = HttpServiceProxyFactory.builder(adapter).build();
-----
 
-For more details and options, such as suppressing error status codes, see the Javadoc of
-`defaultStatusHandler` in `WebClient.Builder`.
-
-For `RestTemplate`:
-
-By default, `RestTemplate` raises `RestClientException` for 4xx and 5xx HTTP status codes.
-To customize this, register an error handler that applies to all responses
-performed through the client:
-
-[source,java,indent=0,subs="verbatim,quotes"]
-----
+	// or for RestTemplate...
 	RestTemplate restTemplate = new RestTemplate();
 	restTemplate.setErrorHandler(myErrorHandler);
-	
+
 	RestTemplateAdapter adapter = RestTemplateAdapter.create(restTemplate);
+
 	HttpServiceProxyFactory factory = HttpServiceProxyFactory.builderFor(adapter).build();
 ----
 
-For more details and options, see the Javadoc of `setErrorHandler` in `RestTemplate` and
-the `ResponseErrorHandler` hierarchy.
+For more details and options such as suppressing error status codes, see the reference
+documentation for each client, as well as the Javadoc of `defaultStatusHandler` in
+`RestClient.Builder` or `WebClient.Builder`, and the `setErrorHandler` of `RestTemplate`.