Polishing in ResourceHttpMessageWriter

See gh-35536

spring-web/src/main/java/org/springframework/http/codec/ResourceHttpMessageWriter.java

@@ -51,12 +51,14 @@ import org.springframework.lang.Nullable;
 import org.springframework.util.MimeTypeUtils;
 
 /**
- * {@code HttpMessageWriter} that can write a {@link Resource}.
+ * {@code HttpMessageWriter} that can write a {@link Resource} from both`` client
+ * and server perspectives.
  *
- * <p>Also an implementation of {@code HttpMessageWriter} with support for writing one
- * or more {@link ResourceRegion}'s based on the HTTP ranges specified in the request.
+ * <p>From a server perspective, the server-side only write method supports
+ * writing one or more {@link ResourceRegion}'s based on HTTP ranges specified
+ * in the request.
  *
- * <p>For reading to a Resource, use {@link ResourceDecoder} wrapped with
+ * <p>To read a Resource, use {@link ResourceDecoder} wrapped with
  * {@link DecoderHttpMessageReader}.
  *
  * @author Arjen Poutsma
@@ -122,16 +124,19 @@ public class ResourceHttpMessageWriter implements HttpMessageWriter<Resource> {
 					if (result != null) {
 						return result;
 					}
-					else {
+
 					Mono<Resource> input = Mono.just(resource);
 					DataBufferFactory factory = message.bufferFactory();
-						Flux<DataBuffer> body = this.encoder.encode(input, factory, type, message.getHeaders().getContentType(), hints)
+					MediaType contentType = message.getHeaders().getContentType();
+
+					Flux<DataBuffer> body = this.encoder.encode(input, factory, type, contentType, hints)
 							.subscribeOn(Schedulers.boundedElastic());
+
 					if (logger.isDebugEnabled()) {
 						body = body.doOnNext(buffer -> Hints.touchDataBuffer(buffer, hints, logger));
 					}
+
 					return message.writeWith(body);
-					}
 				}));
 	}
 
@@ -139,7 +144,10 @@ public class ResourceHttpMessageWriter implements HttpMessageWriter<Resource> {
 	 * Adds the default headers for the given resource to the given message.
 	 * @since 6.1
 	 */
-	public Mono<Void> addDefaultHeaders(ReactiveHttpOutputMessage message, Resource resource, @Nullable MediaType contentType, Map<String, Object> hints) {
+	public Mono<Void> addDefaultHeaders(
+			ReactiveHttpOutputMessage message, Resource resource, @Nullable MediaType contentType,
+			Map<String, Object> hints) {
+
 		return Mono.defer(() -> {
 			HttpHeaders headers = message.getHeaders();
 			MediaType resourceMediaType = getResourceMediaType(contentType, resource, hints);
@@ -149,16 +157,15 @@ public class ResourceHttpMessageWriter implements HttpMessageWriter<Resource> {
 				headers.set(HttpHeaders.ACCEPT_RANGES, "bytes");
 			}
 
-			if (headers.getContentLength() < 0) {
+			if (headers.getContentLength() >= 0) {
+				return Mono.empty();
+			}
+
 			return lengthOf(resource)
 					.flatMap(contentLength -> {
 						headers.setContentLength(contentLength);
 						return Mono.empty();
 					});
-			}
-			else {
-				return Mono.empty();
-			}
 		});
 	}