Add initial RequestHeaderArgumentResolver implementation and tests.

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

@@ -189,6 +189,7 @@ public final class HttpServiceProxyFactory {
 			List<HttpServiceArgumentResolver> resolvers = new ArrayList<>(this.customResolvers);
 			resolvers.add(new HttpMethodArgumentResolver());
 			resolvers.add(new PathVariableArgumentResolver(conversionService));
+			resolvers.add(new RequestHeaderArgumentResolver(conversionService));
 			return resolvers;
 		}
 

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

@@ -66,7 +66,7 @@ public class PathVariableArgumentResolver implements HttpServiceArgumentResolver
 		if (Map.class.isAssignableFrom(parameter.getParameterType())) {
 			if (argument != null) {
 				Assert.isInstanceOf(Map.class, argument);
-				((Map<String, ?>) argument).forEach((key, value) ->
+				((Map<Object, ?>) argument).forEach((key, value) ->
 						addUriParameter(key, value, annotation.required(), requestValues));
 			}
 		}
@@ -81,7 +81,10 @@ public class PathVariableArgumentResolver implements HttpServiceArgumentResolver
 	}
 
 	private void addUriParameter(
-			String name, @Nullable Object value, boolean required, HttpRequestValues.Builder requestValues) {
+			Object name, @Nullable Object value, boolean required, HttpRequestValues.Builder requestValues) {
+
+		String stringName = this.conversionService.convert(name, String.class);
+		Assert.notNull(stringName, "Missing path variable name");
 
 		if (value instanceof Optional) {
 			value = ((Optional<?>) value).orElse(null);
@@ -92,15 +95,15 @@ public class PathVariableArgumentResolver implements HttpServiceArgumentResolver
 		}
 
 		if (value == null) {
-			Assert.isTrue(!required, "Missing required path variable '" + name + "'");
+			Assert.isTrue(!required, "Missing required path variable '" + stringName + "'");
 			return;
 		}
 
 		if (logger.isTraceEnabled()) {
-			logger.trace("Resolved path variable '" + name + "' to " + value);
+			logger.trace("Resolved path variable '" + stringName + "' to " + value);
 		}
 
-		requestValues.setUriVariable(name, (String) value);
+		requestValues.setUriVariable(stringName, (String) value);
 	}
 
 }

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

@@ -0,0 +1,139 @@
+/*
+ * Copyright 2002-2022 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.Arrays;
+import java.util.Collection;
+import java.util.Map;
+import java.util.Objects;
+import java.util.Optional;
+import java.util.stream.Stream;
+
+import org.apache.commons.logging.Log;
+import org.apache.commons.logging.LogFactory;
+
+import org.springframework.core.MethodParameter;
+import org.springframework.core.convert.ConversionService;
+import org.springframework.lang.Nullable;
+import org.springframework.util.Assert;
+import org.springframework.util.StringUtils;
+import org.springframework.web.bind.annotation.RequestHeader;
+import org.springframework.web.bind.annotation.ValueConstants;
+
+/**
+ * An implementation of {@link HttpServiceArgumentResolver} that resolves
+ * request headers based on method arguments annotated
+ * with {@link  RequestHeader}. {@code null} values are allowed only
+ * if {@link RequestHeader#required()} is {@code true}. {@code null}
+ * values are replaced with {@link RequestHeader#defaultValue()} if it
+ * is not equal to {@link ValueConstants#DEFAULT_NONE}.
+ *
+ * @author Olga Maciaszek-Sharma
+ * @since 6.0
+ */
+public class RequestHeaderArgumentResolver implements HttpServiceArgumentResolver {
+
+	private static final Log logger = LogFactory.getLog(RequestHeaderArgumentResolver.class);
+
+	private final ConversionService conversionService;
+
+	public RequestHeaderArgumentResolver(ConversionService conversionService) {
+		Assert.notNull(conversionService, "ConversionService is required");
+		this.conversionService = conversionService;
+	}
+
+	@Override
+	public boolean resolve(@Nullable Object argument, MethodParameter parameter,
+			HttpRequestValues.Builder requestValues) {
+		RequestHeader annotation = parameter.getParameterAnnotation(RequestHeader.class);
+
+		if (annotation == null) {
+			return false;
+		}
+
+		if (Map.class.isAssignableFrom(parameter.getParameterType())) {
+			if (argument != null) {
+				Assert.isInstanceOf(Map.class, argument);
+				((Map<?, ?>) argument).forEach((key, value) ->
+						addRequestHeader(key, value, annotation.required(), annotation.defaultValue(),
+								requestValues));
+			}
+		}
+		else {
+			String name = StringUtils.hasText(annotation.value()) ?
+					annotation.value() : annotation.name();
+			name = StringUtils.hasText(name) ? name : parameter.getParameterName();
+			Assert.notNull(name, "Failed to determine request header name for parameter: " + parameter);
+			addRequestHeader(name, argument, annotation.required(), annotation.defaultValue(),
+					requestValues);
+		}
+		return true;
+	}
+
+	private void addRequestHeader(
+			Object name, @Nullable Object value, boolean required, String defaultValue,
+			HttpRequestValues.Builder requestValues) {
+
+		String stringName = this.conversionService.convert(name, String.class);
+		Assert.notNull(stringName, "Failed to convert request header name '" +
+				name + "' to String");
+
+		if (value instanceof Optional) {
+			value = ((Optional<?>) value).orElse(null);
+		}
+
+		if (value == null) {
+			if (!ValueConstants.DEFAULT_NONE.equals(defaultValue)) {
+				value = defaultValue;
+			}
+			else {
+				Assert.isTrue(!required, "Missing required request header '" + stringName + "'");
+				return;
+			}
+		}
+
+		String[] headerValues = toStringArray(value);
+
+		if (logger.isTraceEnabled()) {
+			logger.trace("Resolved request header '" + stringName + "' to list of values: " +
+					String.join(", ", headerValues));
+		}
+
+		requestValues.addHeader(stringName, headerValues);
+	}
+
+	private String[] toStringArray(Object value) {
+		return toValueStream(value)
+				.filter(Objects::nonNull)
+				.map(headerElement -> headerElement instanceof String
+						? (String) headerElement :
+						this.conversionService.convert(headerElement, String.class))
+				.filter(Objects::nonNull)
+				.toArray(String[]::new);
+	}
+
+	private Stream<?> toValueStream(Object value) {
+		if (value instanceof Object[]) {
+			return Arrays.stream((Object[]) value);
+		}
+		if (value instanceof Collection<?>) {
+			return ((Collection<?>) value).stream();
+		}
+		return Stream.of(value);
+	}
+
+}