Add HttpHeaders argument resolver for HTTP service

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

@@ -937,6 +937,9 @@ method parameters:
 | `HttpMethod`
 | Dynamically set the HTTP method for the request, overriding the annotation's `method` attribute
 
+| `HttpHeaders`
+| Add request headers. Header values are added and do not override already added header values.
+
 | `@RequestHeader`
 | Add a request header or multiple headers. The argument may be a single value,
   a `Collection<?>` of values, `Map<String, ?>`,`MultiValueMap<String, ?>`.

spring-web/src/main/java/org/springframework/web/service/invoker/HttpHeadersArgumentResolver.java

@@ -0,0 +1,65 @@
+/*
+ * Copyright 2002-2025 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.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.springframework.web.service.invoker;
+
+import java.util.Optional;
+
+import org.apache.commons.logging.Log;
+import org.apache.commons.logging.LogFactory;
+import org.jspecify.annotations.Nullable;
+
+import org.springframework.core.MethodParameter;
+import org.springframework.http.HttpHeaders;
+import org.springframework.util.Assert;
+
+/**
+ * {@link HttpServiceArgumentResolver} that resolves the target
+ * request's HTTP headers from an {@link HttpHeaders} argument.
+ *
+ * @author Yanming Zhou
+ */
+public class HttpHeadersArgumentResolver implements HttpServiceArgumentResolver {
+
+	private static final Log logger = LogFactory.getLog(HttpHeadersArgumentResolver.class);
+
+
+	@Override
+	public boolean resolve(
+			@Nullable Object argument, MethodParameter parameter, HttpRequestValues.Builder requestValues) {
+
+		parameter = parameter.nestedIfOptional();
+
+		if (!parameter.getNestedParameterType().equals(HttpHeaders.class)) {
+			return false;
+		}
+
+		if (argument instanceof Optional<?> optionalValue) {
+			argument = optionalValue.orElse(null);
+		}
+
+		if (argument == null) {
+			Assert.isTrue(parameter.isOptional(), "HttpHeaders is required");
+			return true;
+		}
+
+		((HttpHeaders) argument).forEach((name, values) ->
+				requestValues.addHeader(name, values.toArray(new String[0])));
+
+		return true;
+	}
+
+}

spring-web/src/main/java/org/springframework/web/service/invoker/HttpServiceProxyFactory.java

@@ -47,6 +47,7 @@
  * {@link Builder Builder}.
  *
  * @author Rossen Stoyanchev
+ * @author Yanming Zhou
  * @since 6.0
  * @see org.springframework.web.client.support.RestClientAdapter
  * @see org.springframework.web.reactive.function.client.support.WebClientAdapter
@@ -210,6 +211,7 @@ private List<HttpServiceArgumentResolver> initArgumentResolvers() {
 			resolvers.add(new UrlArgumentResolver());
 			resolvers.add(new UriBuilderFactoryArgumentResolver());
 			resolvers.add(new HttpMethodArgumentResolver());
+			resolvers.add(new HttpHeadersArgumentResolver());
 
 			return resolvers;
 		}

spring-web/src/test/java/org/springframework/web/service/invoker/HttpHeadersArgumentResolverTests.java

@@ -0,0 +1,73 @@
+/*
+ * Copyright 2002-2025 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.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.springframework.web.service.invoker;
+
+import org.junit.jupiter.api.Test;
+
+import org.springframework.http.HttpHeaders;
+import org.springframework.web.service.annotation.GetExchange;
+import org.springframework.web.service.annotation.HttpExchange;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+/**
+ * Tests for {@link HttpHeadersArgumentResolver}.
+ *
+ * @author Yanming Zhou
+ */
+class HttpHeadersArgumentResolverTests {
+
+	private final TestExchangeAdapter client = new TestExchangeAdapter();
+
+	private final Service service =
+			HttpServiceProxyFactory.builderFor(this.client).build().createClient(Service.class);
+
+	@Test
+	void headers() {
+		HttpHeaders headers = new HttpHeaders();
+		headers.add("foo", "bar");
+		headers.add("test", "testValue1");
+		headers.add("test", "testValue2");
+		this.service.execute(headers);
+
+		HttpHeaders actualHeaders = this.client.getRequestValues().getHeaders();
+		assertThat(actualHeaders.get("foo")).containsOnly("bar");
+		assertThat(actualHeaders.get("test")).containsExactlyInAnyOrder("testValue1", "testValue2");
+	}
+
+	@Test
+	void doesNotOverrideAnnotationHeaders() {
+		HttpHeaders headers = new HttpHeaders();
+		headers.add("foo", "bar");
+		this.service.executeWithAnnotationHeaders(headers);
+
+		HttpHeaders actualHeaders = this.client.getRequestValues().getHeaders();
+		assertThat(actualHeaders.get("foo")).containsExactlyInAnyOrder("foo", "bar");
+		assertThat(actualHeaders.get("bar")).containsOnly("bar");
+	}
+
+	private interface Service {
+
+		@GetExchange
+		void execute(HttpHeaders headers);
+
+		@HttpExchange(method = "GET", headers = {"foo=foo", "bar=bar"})
+		void executeWithAnnotationHeaders(HttpHeaders headers);
+
+	}
+
+}