Optimize some iterations in BodyExtractor and BodyInserter

This commit turns some stream-based iterations back into simpler
enhanced for loops.

For simple use cases like these, where the stream API is merely used to
map/filter + collect to a List, a for loop is more efficient.
This is especially true for small collections like the ones we deal
with in BodyInserters/BodyExtractors here (in the order of 50ns/op vs
5ns/op). These cases are also simple enough that they don't lose in
readability after the conversion.

Closes gh-30136

spring-web/src/main/java/org/springframework/http/client/reactive/AbstractClientHttpRequest.java

@@ -147,8 +147,10 @@ protected Mono<Void> doCommit(@Nullable Supplier<? extends Publisher<Void>> writ
 			this.commitActions.add(writeAction);
 		}
 
-		List<? extends Publisher<Void>> actions = this.commitActions.stream()
-				.map(Supplier::get).toList();
+		List<Publisher<Void>> actions = new ArrayList<>(this.commitActions.size());
+		for (Supplier<? extends Publisher<Void>> commitAction : this.commitActions) {
+			actions.add(commitAction.get());
+		}
 
 		return Flux.concat(actions).then();
 	}

spring-webflux/src/main/java/org/springframework/web/reactive/function/BodyExtractors.java

@@ -194,18 +194,16 @@ private static <T, S extends Publisher<T>> S readWithMessageReaders(
 		MediaType contentType = Optional.ofNullable(message.getHeaders().getContentType())
 				.orElse(MediaType.APPLICATION_OCTET_STREAM);
 
-		return context.messageReaders().stream()
-				.filter(reader -> reader.canRead(elementType, contentType))
-				.findFirst()
-				.map(BodyExtractors::<T>cast)
-				.map(readerFunction)
-				.orElseGet(() -> {
-					List<MediaType> mediaTypes = context.messageReaders().stream()
-							.flatMap(reader -> reader.getReadableMediaTypes(elementType).stream())
-							.toList();
-					return errorFunction.apply(
-							new UnsupportedMediaTypeException(contentType, mediaTypes, elementType));
-				});
+		for (HttpMessageReader<?> messageReader : context.messageReaders()) {
+			if (messageReader.canRead(elementType, contentType)) {
+				return readerFunction.apply(cast(messageReader));
+			}
+		}
+		List<MediaType> mediaTypes = context.messageReaders().stream()
+				.flatMap(reader -> reader.getReadableMediaTypes(elementType).stream())
+				.toList();
+		return errorFunction.apply(
+				new UnsupportedMediaTypeException(contentType, mediaTypes, elementType));
 	}
 
 	private static <T> Mono<T> readToMono(ReactiveHttpInputMessage message, BodyExtractor.Context context,
@@ -245,12 +243,13 @@ private static <T> Flux<T> unsupportedErrorHandler(
 	private static <T> HttpMessageReader<T> findReader(
 			ResolvableType elementType, MediaType mediaType, BodyExtractor.Context context) {
 
-		return context.messageReaders().stream()
-				.filter(messageReader -> messageReader.canRead(elementType, mediaType))
-				.findFirst()
-				.map(BodyExtractors::<T>cast)
-				.orElseThrow(() -> new IllegalStateException(
-						"No HttpMessageReader for \"" + mediaType + "\" and \"" + elementType + "\""));
+		for (HttpMessageReader<?> messageReader : context.messageReaders()) {
+			if (messageReader.canRead(elementType, mediaType)) {
+				return cast(messageReader);
+			}
+		}
+		throw new IllegalStateException(
+						"No HttpMessageReader for \"" + mediaType + "\" and \"" + elementType + "\"");
 	}
 
 	@SuppressWarnings("unchecked")

spring-webflux/src/main/java/org/springframework/web/reactive/function/BodyInserters.java

@@ -373,12 +373,13 @@ else if (adapter != null) {
 			publisher = Mono.just(body);
 		}
 		MediaType mediaType = outputMessage.getHeaders().getContentType();
-		return context.messageWriters().stream()
-				.filter(messageWriter -> messageWriter.canWrite(bodyType, mediaType))
-				.findFirst()
-				.map(BodyInserters::cast)
-				.map(writer -> write(publisher, bodyType, mediaType, outputMessage, context, writer))
-				.orElseGet(() -> Mono.error(unsupportedError(bodyType, context, mediaType)));
+		for (HttpMessageWriter<?> messageWriter : context.messageWriters()) {
+			if (messageWriter.canWrite(bodyType, mediaType)) {
+				HttpMessageWriter<Object> typedMessageWriter = cast(messageWriter);
+				return write(publisher, bodyType, mediaType, outputMessage, context, typedMessageWriter);
+			}
+		}
+		return Mono.error(unsupportedError(bodyType, context, mediaType));
 	}
 
 	private static UnsupportedMediaTypeException unsupportedError(ResolvableType bodyType,
@@ -406,12 +407,13 @@ private static <T> Mono<Void> write(Publisher<? extends T> input, ResolvableType
 	private static <T> HttpMessageWriter<T> findWriter(
 			BodyInserter.Context context, ResolvableType elementType, @Nullable MediaType mediaType) {
 
-		return context.messageWriters().stream()
-				.filter(messageWriter -> messageWriter.canWrite(elementType, mediaType))
-				.findFirst()
-				.map(BodyInserters::<T>cast)
-				.orElseThrow(() -> new IllegalStateException(
-						"No HttpMessageWriter for \"" + mediaType + "\" and \"" + elementType + "\""));
+		for (HttpMessageWriter<?> messageWriter : context.messageWriters()) {
+			if (messageWriter.canWrite(elementType, mediaType)) {
+				return cast(messageWriter);
+			}
+		}
+		throw new IllegalStateException(
+						"No HttpMessageWriter for \"" + mediaType + "\" and \"" + elementType + "\"");
 	}
 
 	@SuppressWarnings("unchecked")