HTTP Service proxy sets body type

Closes gh-34793

spring-web/src/test/java/org/springframework/web/client/support/RestClientAdapterTests.java

@@ -22,7 +22,9 @@ import java.lang.annotation.Retention;
 import java.lang.annotation.RetentionPolicy;
 import java.lang.annotation.Target;
 import java.net.URI;
+import java.util.LinkedHashSet;
 import java.util.Optional;
+import java.util.Set;
 import java.util.function.BiFunction;
 import java.util.stream.Stream;
 
@@ -267,6 +269,19 @@ class RestClientAdapterTests {
 		assertThat(this.anotherServer.getRequestCount()).isEqualTo(0);
 	}
 
+	@ParameterizedAdapterTest // gh-34793
+	void postSet(MockWebServer server, Service service) throws InterruptedException {
+		Set<Person> persons = new LinkedHashSet<>();
+		persons.add(new Person("John"));
+		persons.add(new Person("Richard"));
+		service.postPersonSet(persons);
+
+		RecordedRequest request = server.takeRequest();
+		assertThat(request.getMethod()).isEqualTo("POST");
+		assertThat(request.getPath()).isEqualTo("/persons");
+		assertThat(request.getBody().readUtf8()).isEqualTo("[{\"name\":\"John\"},{\"name\":\"Richard\"}]");
+	}
+
 
 	private static MockWebServer anotherServer() {
 		MockWebServer server = new MockWebServer();
@@ -297,6 +312,9 @@ class RestClientAdapterTests {
 		@PostExchange
 		void postMultipart(MultipartFile file, @RequestPart String anotherPart);
 
+		@PostExchange(url = "/persons", contentType = MediaType.APPLICATION_JSON_VALUE)
+		void postPersonSet(@RequestBody Set<Person> set);
+
 		@PutExchange
 		void putWithCookies(@CookieValue String firstCookie, @CookieValue String secondCookie);
 
@@ -315,4 +333,19 @@ class RestClientAdapterTests {
 		ResponseEntity<String> getWithIgnoredUriBuilderFactory(URI uri, UriBuilderFactory uriBuilderFactory);
 	}
 
+
+	static final class Person {
+
+		private final String name;
+
+		Person(String name) {
+			this.name = name;
+		}
+
+		public String getName() {
+			return this.name;
+		}
+
+	}
+
 }

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

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2024 the original author or authors.
+ * 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.
@@ -54,6 +54,7 @@ class RequestBodyArgumentResolverTests {
 		this.service.execute(body);
 
 		assertThat(getBodyValue()).isEqualTo(body);
+		assertThat(getBodyValueType()).isEqualTo(new ParameterizedTypeReference<String>() {});
 		assertThat(getPublisherBody()).isNull();
 	}
 
@@ -173,6 +174,11 @@ class RequestBodyArgumentResolverTests {
 		return getReactiveRequestValues().getBodyValue();
 	}
 
+	@Nullable
+	private ParameterizedTypeReference<?> getBodyValueType() {
+		return getReactiveRequestValues().getBodyValueType();
+	}
+
 	@Nullable
 	private Publisher<?> getPublisherBody() {
 		return getReactiveRequestValues().getBodyPublisher();