Add ReactiveHttpRequestValues

Separate collection and handling of reactive request values into a
subclass of HttpRequestValues.

Closes gh-30117

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

@@ -27,10 +27,10 @@ import org.reactivestreams.Publisher;
 
 import org.springframework.core.ParameterizedTypeReference;
 import org.springframework.core.ResolvableType;
+import org.springframework.http.HttpEntity;
 import org.springframework.http.HttpHeaders;
 import org.springframework.http.HttpMethod;
 import org.springframework.http.MediaType;
-import org.springframework.http.client.MultipartBodyBuilder;
 import org.springframework.lang.Nullable;
 import org.springframework.util.Assert;
 import org.springframework.util.CollectionUtils;
@@ -48,7 +48,7 @@ import org.springframework.web.util.UriUtils;
  * @author Rossen Stoyanchev
  * @since 6.0
  */
-public final class HttpRequestValues {
+public class HttpRequestValues {
 
 	private static final MultiValueMap<String, String> EMPTY_COOKIES_MAP =
 			CollectionUtils.toMultiValueMap(Collections.emptyMap());
@@ -74,18 +74,11 @@ public final class HttpRequestValues {
 	@Nullable
 	private final Object bodyValue;
 
-	@Nullable
-	private final Publisher<?> body;
 
-	@Nullable
-	private final ParameterizedTypeReference<?> bodyElementType;
-
-
-	private HttpRequestValues(@Nullable HttpMethod httpMethod,
+	protected HttpRequestValues(@Nullable HttpMethod httpMethod,
 			@Nullable URI uri, @Nullable String uriTemplate, Map<String, String> uriVariables,
 			HttpHeaders headers, MultiValueMap<String, String> cookies, Map<String, Object> attributes,
-			@Nullable Object bodyValue,
-			@Nullable Publisher<?> body, @Nullable ParameterizedTypeReference<?> bodyElementType) {
+			@Nullable Object bodyValue) {
 
 		Assert.isTrue(uri != null || uriTemplate != null, "Neither URI nor URI template");
 
@@ -97,8 +90,6 @@ public final class HttpRequestValues {
 		this.cookies = cookies;
 		this.attributes = attributes;
 		this.bodyValue = bodyValue;
-		this.body = body;
-		this.bodyElementType = bodyElementType;
 	}
 
 
@@ -161,8 +152,6 @@ public final class HttpRequestValues {
 
 	/**
 	 * Return the request body as a value to be serialized, if set.
-	 * <p>This is mutually exclusive with {@link #getBody()}.
-	 * Only one of the two or neither is set.
 	 */
 	@Nullable
 	public Object getBodyValue() {
@@ -173,18 +162,24 @@ public final class HttpRequestValues {
 	 * Return the request body as a Publisher.
 	 * <p>This is mutually exclusive with {@link #getBodyValue()}.
 	 * Only one of the two or neither is set.
+	 * @deprecated in favor of {@link ReactiveHttpRequestValues#getBodyPublisher()};
+	 * to be removed in 6.2
 	 */
+	@Deprecated(since = "6.1", forRemoval = true)
 	@Nullable
 	public Publisher<?> getBody() {
-		return this.body;
+		throw new UnsupportedOperationException();
 	}
 
 	/**
-	 * Return the element type for a {@linkplain #getBody() Publisher body}.
+	 * Return the element type for a Publisher body.
+	 * @deprecated in favor of {@link ReactiveHttpRequestValues#getBodyPublisherElementType()};
+	 * to be removed in 6.2
 	 */
+	@Deprecated(since = "6.1", forRemoval = true)
 	@Nullable
 	public ParameterizedTypeReference<?> getBodyElementType() {
-		return this.bodyElementType;
+		throw new UnsupportedOperationException();
 	}
 
 
@@ -196,7 +191,7 @@ public final class HttpRequestValues {
 	/**
 	 * Builder for {@link HttpRequestValues}.
 	 */
-	public final static class Builder {
+	public static class Builder {
 
 		@Nullable
 		private HttpMethod httpMethod;
@@ -220,7 +215,7 @@ public final class HttpRequestValues {
 		private MultiValueMap<String, String> requestParams;
 
 		@Nullable
-		private MultipartBodyBuilder multipartBuilder;
+		private MultiValueMap<String, Object> parts;
 
 		@Nullable
 		private Map<String, Object> attributes;
@@ -228,12 +223,6 @@ public final class HttpRequestValues {
 		@Nullable
 		private Object bodyValue;
 
-		@Nullable
-		private Publisher<?> body;
-
-		@Nullable
-		private ParameterizedTypeReference<?> bodyElementType;
-
 		/**
 		 * Set the HTTP method for the request.
 		 */
@@ -327,23 +316,30 @@ public final class HttpRequestValues {
 		}
 
 		/**
-		 * Add a part to a multipart request. The part value may be as described
-		 * in {@link MultipartBodyBuilder#part(String, Object)}.
+		 * Add a part for a multipart request. The part may be:
+		 * <ul>
+		 * <li>String -- form field
+		 * <li>{@link org.springframework.core.io.Resource Resource} -- file part
+		 * <li>Object -- content to be encoded (e.g. to JSON)
+		 * <li>{@link HttpEntity} -- part content and headers although generally it's
+		 * easier to add headers through the returned builder
+		 * </ul>
 		 */
 		public Builder addRequestPart(String name, Object part) {
-			this.multipartBuilder = (this.multipartBuilder != null ? this.multipartBuilder : new MultipartBodyBuilder());
-			this.multipartBuilder.part(name, part);
+			this.parts = (this.parts != null ? this.parts : new LinkedMultiValueMap<>());
+			this.parts.add(name, part);
 			return this;
 		}
 
 		/**
 		 * Variant of {@link #addRequestPart(String, Object)} that allows the
 		 * part value to be produced by a {@link Publisher}.
+		 * @deprecated in favor of {@link ReactiveHttpRequestValues.Builder#addRequestPartPublisher};
+		 * to be removed in 6.2
 		 */
+		@Deprecated(since = "6.1", forRemoval = true)
 		public <T, P extends Publisher<T>> Builder addRequestPart(String name, P publisher, ResolvableType type) {
-			this.multipartBuilder = (this.multipartBuilder != null ? this.multipartBuilder : new MultipartBodyBuilder());
-			this.multipartBuilder.asyncPart(name, publisher, ParameterizedTypeReference.forType(type.getType()));
-			return this;
+			throw new UnsupportedOperationException();
 		}
 
 		/**
@@ -358,25 +354,22 @@ public final class HttpRequestValues {
 		}
 
 		/**
-		 * Set the request body as a concrete value to be serialized.
-		 * <p>This is mutually exclusive with, and resets any previously set
-		 * {@linkplain #setBody(Publisher, ParameterizedTypeReference) body Publisher}.
+		 * Set the request body as an Object to be serialized.
 		 */
 		public void setBodyValue(Object bodyValue) {
 			this.bodyValue = bodyValue;
-			this.body = null;
-			this.bodyElementType = null;
 		}
 
 		/**
-		 * Set the request body as a concrete value to be serialized.
+		 * Set the request body as a Reactive Streams Publisher.
 		 * <p>This is mutually exclusive with, and resets any previously set
 		 * {@linkplain #setBodyValue(Object) body value}.
+		 * @deprecated in favor of {@link ReactiveHttpRequestValues.Builder#setBodyPublisher};
+		 * to be removed in 6.2
 		 */
+		@Deprecated(since = "6.1", forRemoval = true)
 		public <T, P extends Publisher<T>> void setBody(P body, ParameterizedTypeReference<T> elementTye) {
-			this.body = body;
-			this.bodyElementType = elementTye;
-			this.bodyValue = null;
+			throw new UnsupportedOperationException();
 		}
 
 		/**
@@ -389,15 +382,15 @@ public final class HttpRequestValues {
 			Map<String, String> uriVars = (this.uriVars != null ? new HashMap<>(this.uriVars) : Collections.emptyMap());
 
 			Object bodyValue = this.bodyValue;
-			if (this.multipartBuilder != null) {
-				Assert.isTrue(bodyValue == null && this.body == null, "Expected body or request parts, not both");
-				bodyValue = this.multipartBuilder.build();
+			if (hasParts()) {
+				Assert.isTrue(!hasBody(), "Expected body or request parts, not both");
+				bodyValue = buildMultipartBody();
 			}
 
 			if (!CollectionUtils.isEmpty(this.requestParams)) {
-				if (hasContentType(MediaType.APPLICATION_FORM_URLENCODED)) {
-					Assert.isTrue(this.multipartBuilder == null, "Cannot add parts to form data request");
-					Assert.isTrue(bodyValue == null && this.body == null, "Cannot set body of form data request");
+				if (hasFormDataContentType()) {
+					Assert.isTrue(!hasParts(), "Request parts not expected for a form data request");
+					Assert.isTrue(!hasBody(), "Body not expected for a form data request");
 					bodyValue = new LinkedMultiValueMap<>(this.requestParams);
 				}
 				else if (uri != null) {
@@ -426,13 +419,26 @@ public final class HttpRequestValues {
 			Map<String, Object> attributes = (this.attributes != null ?
 					new HashMap<>(this.attributes) : Collections.emptyMap());
 
-			return new HttpRequestValues(
-					this.httpMethod, uri, uriTemplate, uriVars, headers, cookies, attributes,
-					bodyValue, this.body, this.bodyElementType);
+			return createRequestValues(
+					this.httpMethod, uri, uriTemplate, uriVars, headers, cookies, attributes, bodyValue);
 		}
 
-		private boolean hasContentType(MediaType mediaType) {
-			return (this.headers != null && mediaType.equals(this.headers.getContentType()));
+		protected boolean hasParts() {
+			return (this.parts != null);
+		}
+
+		protected boolean hasBody() {
+			return (this.bodyValue != null);
+		}
+
+		protected Object buildMultipartBody() {
+			Assert.notNull(this.parts, "`parts` is null, was hasParts() not called?");
+			return this.parts;
+		}
+
+		private boolean hasFormDataContentType() {
+			return (this.headers != null &&
+					MediaType.APPLICATION_FORM_URLENCODED.equals(this.headers.getContentType()));
 		}
 
 		private String appendQueryParams(
@@ -453,6 +459,15 @@ public final class HttpRequestValues {
 			return uriComponentsBuilder.build().toUriString();
 		}
 
+		protected HttpRequestValues createRequestValues(
+				@Nullable HttpMethod httpMethod,
+				@Nullable URI uri, @Nullable String uriTemplate, Map<String, String> uriVars,
+				HttpHeaders headers, MultiValueMap<String, String> cookies, Map<String, Object> attributes,
+				@Nullable Object bodyValue) {
+
+			return new HttpRequestValues(
+					this.httpMethod, uri, uriTemplate, uriVars, headers, cookies, attributes, bodyValue);
+		}
 	}
 
 }

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

@@ -22,6 +22,7 @@ import java.util.Arrays;
 import java.util.List;
 import java.util.Optional;
 import java.util.function.Function;
+import java.util.function.Supplier;
 
 import org.reactivestreams.Publisher;
 import reactor.core.publisher.Flux;
@@ -81,13 +82,16 @@ final class HttpServiceMethod {
 		this.parameters = initMethodParameters(method);
 		this.argumentResolvers = argumentResolvers;
 
-		this.requestValuesInitializer =
-				HttpRequestValuesInitializer.create(method, containingClass, embeddedValueResolver);
+		boolean isReactorAdapter = (REACTOR_PRESENT && adapter instanceof ReactorHttpExchangeAdapter);
 
-		this.responseFunction =
-				(REACTOR_PRESENT && adapter instanceof ReactorHttpExchangeAdapter reactorAdapter ?
-						ReactorExchangeResponseFunction.create(reactorAdapter, method) :
-						ExchangeResponseFunction.create(adapter, method));
+		this.requestValuesInitializer =
+				HttpRequestValuesInitializer.create(
+						method, containingClass, embeddedValueResolver,
+						(isReactorAdapter ? ReactiveHttpRequestValues::builder : HttpRequestValues::builder));
+
+		this.responseFunction = (isReactorAdapter ?
+				ReactorExchangeResponseFunction.create((ReactorHttpExchangeAdapter) adapter, method) :
+				ExchangeResponseFunction.create(adapter, method));
 	}
 
 	private static MethodParameter[] initMethodParameters(Method method) {
@@ -147,20 +151,11 @@ final class HttpServiceMethod {
 	 */
 	private record HttpRequestValuesInitializer(
 			@Nullable HttpMethod httpMethod, @Nullable String url,
-			@Nullable MediaType contentType, @Nullable List<MediaType> acceptMediaTypes) {
-
-		private HttpRequestValuesInitializer(
-				HttpMethod httpMethod, @Nullable String url,
-				@Nullable MediaType contentType, @Nullable List<MediaType> acceptMediaTypes) {
-
-			this.url = url;
-			this.httpMethod = httpMethod;
-			this.contentType = contentType;
-			this.acceptMediaTypes = acceptMediaTypes;
-		}
+			@Nullable MediaType contentType, @Nullable List<MediaType> acceptMediaTypes,
+			Supplier<HttpRequestValues.Builder> requestValuesSupplier) {
 
 		public HttpRequestValues.Builder initializeRequestValuesBuilder() {
-			HttpRequestValues.Builder requestValues = HttpRequestValues.builder();
+			HttpRequestValues.Builder requestValues = this.requestValuesSupplier.get();
 			if (this.httpMethod != null) {
 				requestValues.setHttpMethod(this.httpMethod);
 			}
@@ -181,7 +176,8 @@ final class HttpServiceMethod {
 		 * Introspect the method and create the request factory for it.
 		 */
 		public static HttpRequestValuesInitializer create(
-				Method method, Class<?> containingClass, @Nullable StringValueResolver embeddedValueResolver) {
+				Method method, Class<?> containingClass, @Nullable StringValueResolver embeddedValueResolver,
+				Supplier<HttpRequestValues.Builder> requestValuesSupplier) {
 
 			HttpExchange annot1 = AnnotatedElementUtils.findMergedAnnotation(containingClass, HttpExchange.class);
 			HttpExchange annot2 = AnnotatedElementUtils.findMergedAnnotation(method, HttpExchange.class);
@@ -193,7 +189,8 @@ final class HttpServiceMethod {
 			MediaType contentType = initContentType(annot1, annot2);
 			List<MediaType> acceptableMediaTypes = initAccept(annot1, annot2);
 
-			return new HttpRequestValuesInitializer(httpMethod, url, contentType, acceptableMediaTypes);
+			return new HttpRequestValuesInitializer(
+					httpMethod, url, contentType, acceptableMediaTypes, requestValuesSupplier);
 		}
 
 		@Nullable

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

@@ -0,0 +1,275 @@
+/*
+ * Copyright 2002-2023 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.net.URI;
+import java.util.List;
+import java.util.Map;
+
+import org.reactivestreams.Publisher;
+
+import org.springframework.core.ParameterizedTypeReference;
+import org.springframework.core.ResolvableType;
+import org.springframework.http.HttpHeaders;
+import org.springframework.http.HttpMethod;
+import org.springframework.http.MediaType;
+import org.springframework.http.client.MultipartBodyBuilder;
+import org.springframework.lang.Nullable;
+import org.springframework.util.Assert;
+import org.springframework.util.MultiValueMap;
+
+/**
+ * {@link HttpRequestValues} extension for use with {@link ReactorHttpExchangeAdapter}.
+ *
+ * @author Rossen Stoyanchev
+ * @since 6.1
+ */
+public final class ReactiveHttpRequestValues extends HttpRequestValues {
+
+	@Nullable
+	private final Publisher<?> body;
+
+	@Nullable
+	private final ParameterizedTypeReference<?> bodyElementType;
+
+
+	private ReactiveHttpRequestValues(
+			@Nullable HttpMethod httpMethod,
+			@Nullable URI uri, @Nullable String uriTemplate, Map<String, String> uriVariables,
+			HttpHeaders headers, MultiValueMap<String, String> cookies, Map<String, Object> attributes,
+			@Nullable Object bodyValue, @Nullable Publisher<?> body, @Nullable ParameterizedTypeReference<?> elementType) {
+
+		super(httpMethod, uri, uriTemplate, uriVariables, headers, cookies, attributes, bodyValue);
+
+		this.body = body;
+		this.bodyElementType = elementType;
+	}
+
+
+	/**
+	 * Return a {@link Publisher} that will produce for the request body.
+	 * <p>This is mutually exclusive with {@link #getBodyValue()}.
+	 * Only one of the two or neither is set.
+	 */
+	@Nullable
+	public Publisher<?> getBodyPublisher() {
+		return this.body;
+	}
+
+	/**
+	 * Return the element type for a {@linkplain #getBodyPublisher() Publisher body}.
+	 */
+	@Nullable
+	public ParameterizedTypeReference<?> getBodyPublisherElementType() {
+		return this.bodyElementType;
+	}
+
+	/**
+	 * Return the request body as a Publisher.
+	 * <p>This is mutually exclusive with {@link #getBodyValue()}.
+	 * Only one of the two or neither is set.
+	 */
+	@SuppressWarnings("removal")
+	@Nullable
+	public Publisher<?> getBody() {
+		return getBodyPublisher();
+	}
+
+	/**
+	 * Return the element type for a {@linkplain #getBodyPublisher() Publisher body}.
+	 */
+	@SuppressWarnings("removal")
+	@Nullable
+	public ParameterizedTypeReference<?> getBodyElementType() {
+		return getBodyPublisherElementType();
+	}
+
+
+	public static Builder builder() {
+		return new Builder();
+	}
+
+
+	/**
+	 * Builder for {@link ReactiveHttpRequestValues}.
+	 */
+	public final static class Builder extends HttpRequestValues.Builder {
+
+		@Nullable
+		private MultipartBodyBuilder multipartBuilder;
+
+		@Nullable
+		private Publisher<?> body;
+
+		@Nullable
+		private ParameterizedTypeReference<?> bodyElementType;
+
+		@Override
+		public Builder setHttpMethod(HttpMethod httpMethod) {
+			super.setHttpMethod(httpMethod);
+			return this;
+		}
+
+		@Override
+		public Builder setUri(URI uri) {
+			super.setUri(uri);
+			return this;
+		}
+
+		@Override
+		public Builder setUriTemplate(String uriTemplate) {
+			super.setUriTemplate(uriTemplate);
+			return this;
+		}
+
+		@Override
+		public Builder setUriVariable(String name, String value) {
+			super.setUriVariable(name, value);
+			return this;
+		}
+
+		@Override
+		public Builder setAccept(List<MediaType> acceptableMediaTypes) {
+			super.setAccept(acceptableMediaTypes);
+			return this;
+		}
+
+		@Override
+		public Builder setContentType(MediaType contentType) {
+			super.setContentType(contentType);
+			return this;
+		}
+
+		@Override
+		public Builder addHeader(String headerName, String... headerValues) {
+			super.addHeader(headerName, headerValues);
+			return this;
+		}
+
+		@Override
+		public Builder addCookie(String name, String... values) {
+			super.addCookie(name, values);
+			return this;
+		}
+
+		@Override
+		public Builder addRequestParameter(String name, String... values) {
+			super.addRequestParameter(name, values);
+			return this;
+		}
+
+		@Override
+		public Builder addAttribute(String name, Object value) {
+			super.addAttribute(name, value);
+			return this;
+		}
+
+		/**
+		 * Add a part to a multipart request. The part value may be as described
+		 * in {@link MultipartBodyBuilder#part(String, Object)}.
+		 */
+		@Override
+		public Builder addRequestPart(String name, Object part) {
+			this.multipartBuilder = (this.multipartBuilder != null ? this.multipartBuilder : new MultipartBodyBuilder());
+			this.multipartBuilder.part(name, part);
+			return this;
+		}
+
+		/**
+		 * Variant of {@link #addRequestPart(String, Object)} that allows the
+		 * part value to be produced by a {@link Publisher}.
+		 */
+		public <T, P extends Publisher<T>> Builder addRequestPartPublisher(
+				String name, P publisher, ParameterizedTypeReference<T> elementTye) {
+
+			this.multipartBuilder = (this.multipartBuilder != null ? this.multipartBuilder : new MultipartBodyBuilder());
+			this.multipartBuilder.asyncPart(name, publisher, elementTye);
+			return this;
+		}
+
+		@SuppressWarnings("removal")
+		@Override
+		public <T, P extends Publisher<T>> Builder addRequestPart(String name, P publisher, ResolvableType type) {
+			return addRequestPartPublisher(name, publisher, ParameterizedTypeReference.forType(type.getType()));
+		}
+
+		/**
+		 * {@inheritDoc}
+		 * <p>This is mutually exclusive with, and resets any previously set
+		 * {@linkplain #setBodyPublisher(Publisher, ParameterizedTypeReference)}.
+		 */
+		@Override
+		public void setBodyValue(Object bodyValue) {
+			super.setBodyValue(bodyValue);
+			this.body = null;
+			this.bodyElementType = null;
+		}
+
+		/**
+		 * Set the request body as a Reactive Streams Publisher.
+		 * <p>This is mutually exclusive with, and resets any previously set
+		 * {@linkplain #setBodyValue(Object) body value}.
+		 */
+		@SuppressWarnings("DataFlowIssue")
+		public <T, P extends Publisher<T>> void setBodyPublisher(P body, ParameterizedTypeReference<T> elementTye) {
+			this.body = body;
+			this.bodyElementType = elementTye;
+			super.setBodyValue(null);
+		}
+
+		@SuppressWarnings("removal")
+		@Override
+		public <T, P extends Publisher<T>> void setBody(P body, ParameterizedTypeReference<T> elementTye) {
+			setBodyPublisher(body, elementTye);
+		}
+
+		@Override
+		public ReactiveHttpRequestValues build() {
+			return (ReactiveHttpRequestValues) super.build();
+		}
+
+		@Override
+		protected boolean hasParts() {
+			return (this.multipartBuilder != null);
+		}
+
+		@Override
+		protected boolean hasBody() {
+			return (super.hasBody() || this.body != null);
+		}
+
+		@Override
+		protected Object buildMultipartBody() {
+			Assert.notNull(this.multipartBuilder, "`multipartBuilder` is null, was hasParts() not called?");
+			return this.multipartBuilder.build();
+		}
+
+		@Override
+		protected ReactiveHttpRequestValues createRequestValues(
+				@Nullable HttpMethod httpMethod,
+				@Nullable URI uri, @Nullable String uriTemplate, Map<String, String> uriVars,
+				HttpHeaders headers, MultiValueMap<String, String> cookies, Map<String, Object> attributes,
+				@Nullable Object bodyValue) {
+
+			return new ReactiveHttpRequestValues(
+					httpMethod, uri, uriTemplate, uriVars, headers, cookies, attributes,
+					bodyValue, this.body, this.bodyElementType);
+		}
+
+	}
+
+}

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

@@ -78,9 +78,14 @@ public class RequestBodyArgumentResolver implements HttpServiceArgumentResolver
 					Assert.isTrue(!adapter.isNoValue(), message);
 					Assert.isTrue(nestedParameter.getNestedParameterType() != Void.class, message);
 
-					requestValues.setBody(
-							adapter.toPublisher(argument),
-							ParameterizedTypeReference.forType(nestedParameter.getNestedGenericParameterType()));
+					if (requestValues instanceof ReactiveHttpRequestValues.Builder reactiveRequestValues) {
+						reactiveRequestValues.setBodyPublisher(
+								adapter.toPublisher(argument), asParameterizedTypeRef(nestedParameter));
+					}
+					else {
+						throw new IllegalStateException(
+								"RequestBody with a reactive type is only supported with reactive client");
+					}
 
 					return true;
 				}
@@ -93,4 +98,8 @@ public class RequestBodyArgumentResolver implements HttpServiceArgumentResolver
 		return true;
 	}
 
+	private static ParameterizedTypeReference<Object> asParameterizedTypeRef(MethodParameter nestedParam) {
+		return ParameterizedTypeReference.forType(nestedParam.getNestedGenericParameterType());
+	}
+
 }

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

@@ -19,9 +19,9 @@ package org.springframework.web.service.invoker;
 import org.reactivestreams.Publisher;
 
 import org.springframework.core.MethodParameter;
+import org.springframework.core.ParameterizedTypeReference;
 import org.springframework.core.ReactiveAdapter;
 import org.springframework.core.ReactiveAdapterRegistry;
-import org.springframework.core.ResolvableType;
 import org.springframework.http.HttpEntity;
 import org.springframework.http.codec.multipart.Part;
 import org.springframework.lang.Nullable;
@@ -89,9 +89,20 @@ public class RequestPartArgumentResolver extends AbstractNamedValueArgumentResol
 			Class<?> type = parameter.getParameterType();
 			ReactiveAdapter adapter = this.reactiveAdapterRegistry.getAdapter(type);
 			if (adapter != null) {
-				Assert.isTrue(!adapter.isNoValue(), "Expected publisher that produces a value");
-				Publisher<?> publisher = adapter.toPublisher(value);
-				requestValues.addRequestPart(name, publisher, ResolvableType.forMethodParameter(parameter.nested()));
+				MethodParameter nestedParameter = parameter.nested();
+
+				String message = "Async type for @RequestPart should produce value(s)";
+				Assert.isTrue(!adapter.isNoValue(), message);
+				Assert.isTrue(nestedParameter.getNestedParameterType() != Void.class, message);
+
+				if (requestValues instanceof ReactiveHttpRequestValues.Builder reactiveValues) {
+					reactiveValues.addRequestPartPublisher(
+							name, adapter.toPublisher(value), asParameterizedTypeRef(nestedParameter));
+				}
+				else {
+					throw new IllegalStateException(
+							"RequestPart with a reactive type is only supported with reactive client");
+				}
 				return;
 			}
 		}
@@ -99,4 +110,8 @@ public class RequestPartArgumentResolver extends AbstractNamedValueArgumentResol
 		requestValues.addRequestPart(name, value);
 	}
 
+	private static ParameterizedTypeReference<Object> asParameterizedTypeRef(MethodParameter nestedParam) {
+		return ParameterizedTypeReference.forType(nestedParam.getNestedGenericParameterType());
+	}
+
 }