Enable RestClient.defaultRequest

This commit enables the defaultRequest setting in the RestClient
builder.

Closes gh-32028

spring-web/src/main/java/org/springframework/web/client/DefaultRestClient.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2023 the original author or authors.
+ * Copyright 2002-2024 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -99,6 +99,9 @@ final class DefaultRestClient implements RestClient {
 	@Nullable
 	private final HttpHeaders defaultHeaders;
 
+	@Nullable
+	private final Consumer<RequestHeadersSpec<?>> defaultRequest;
+
 	private final List<StatusHandler> defaultStatusHandlers;
 
 	private final DefaultRestClientBuilder builder;
@@ -116,6 +119,7 @@ final class DefaultRestClient implements RestClient {
 			@Nullable List<ClientHttpRequestInitializer> initializers,
 			UriBuilderFactory uriBuilderFactory,
 			@Nullable HttpHeaders defaultHeaders,
+			@Nullable Consumer<RequestHeadersSpec<?>> defaultRequest,
 			@Nullable List<StatusHandler> statusHandlers,
 			List<HttpMessageConverter<?>> messageConverters,
 			ObservationRegistry observationRegistry,
@@ -127,6 +131,7 @@ final class DefaultRestClient implements RestClient {
 		this.interceptors = interceptors;
 		this.uriBuilderFactory = uriBuilderFactory;
 		this.defaultHeaders = defaultHeaders;
+		this.defaultRequest = defaultRequest;
 		this.defaultStatusHandlers = (statusHandlers != null ? new ArrayList<>(statusHandlers) : new ArrayList<>());
 		this.messageConverters = messageConverters;
 		this.observationRegistry = observationRegistry;
@@ -451,6 +456,9 @@ private <T> T exchangeInternal(ExchangeFunction<T> exchangeFunction, boolean clo
 			Observation observation = null;
 			URI uri = null;
 			try {
+				if (DefaultRestClient.this.defaultRequest != null) {
+					DefaultRestClient.this.defaultRequest.accept(this);
+				}
 				uri = initUri();
 				HttpHeaders headers = initHeaders();
 				ClientHttpRequest clientRequest = createRequest(uri);

spring-web/src/main/java/org/springframework/web/client/DefaultRestClientBuilder.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2023 the original author or authors.
+ * Copyright 2002-2024 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -371,6 +371,7 @@ public RestClient build() {
 		return new DefaultRestClient(requestFactory,
 				this.interceptors, this.initializers, uriBuilderFactory,
 				defaultHeaders,
+				this.defaultRequest,
 				this.statusHandlers,
 				messageConverters,
 				this.observationRegistry,

spring-web/src/test/java/org/springframework/web/client/RestClientIntegrationTests.java

@@ -856,6 +856,50 @@ void filterForErrorHandling(ClientHttpRequestFactory requestFactory) {
 		expectRequestCount(2);
 	}
 
+	@ParameterizedRestClientTest
+	void defaultHeaders(ClientHttpRequestFactory requestFactory) {
+		startServer(requestFactory);
+
+		prepareResponse(response -> response.setHeader("Content-Type", "text/plain")
+				.setBody("Hello Spring!"));
+
+		RestClient headersClient = this.restClient.mutate()
+				.defaultHeaders(headers -> headers.add("foo", "bar"))
+				.build();
+
+		String result = headersClient.get()
+				.uri("/greeting")
+				.retrieve()
+				.body(String.class);
+
+		assertThat(result).isEqualTo("Hello Spring!");
+
+		expectRequestCount(1);
+		expectRequest(request -> assertThat(request.getHeader("foo")).isEqualTo("bar"));
+	}
+
+	@ParameterizedRestClientTest
+	void defaultRequest(ClientHttpRequestFactory requestFactory) {
+		startServer(requestFactory);
+
+		prepareResponse(response -> response.setHeader("Content-Type", "text/plain")
+				.setBody("Hello Spring!"));
+
+		RestClient headersClient = this.restClient.mutate()
+				.defaultRequest(request -> request.header("foo", "bar"))
+				.build();
+
+		String result = headersClient.get()
+				.uri("/greeting")
+				.retrieve()
+				.body(String.class);
+
+		assertThat(result).isEqualTo("Hello Spring!");
+
+		expectRequestCount(1);
+		expectRequest(request -> assertThat(request.getHeader("foo")).isEqualTo("bar"));
+	}
+
 
 	private void prepareResponse(Consumer<MockResponse> consumer) {
 		MockResponse response = new MockResponse();