Introduce 'useRegisteredExtensionsOnly' property in classes using MediaTypeFactory

This commit introduces a `useRegisteredExtensionsOnly` property that
indicates whether classes that use the `MediaTypeFactory` for supplying
default media types can do so.

 - In classes that were introduced in Spring 5.0, the
 `useRegisteredExtensionsOnly` property takes the place of the
 `useJaf` property that was removed in 0aaa652
 - In classes that existed before Spring 5.0, the
 `useRegisteredExtensionsOnly` property is added in addition to the
 deprecated `useJaf`, the latter delegating to the former, but with
 flipped behavior.

Issue: SPR-14908

spring-webflux/src/main/java/org/springframework/web/reactive/accept/PathExtensionContentTypeResolver.java

@@ -42,6 +42,8 @@ import org.springframework.web.util.UriUtils;
  */
 public class PathExtensionContentTypeResolver extends AbstractMappingContentTypeResolver {
 
+	private boolean useRegisteredExtensionsOnly = false;
+
 	private boolean ignoreUnknownExtensions = true;
 
 
@@ -61,6 +63,15 @@ public class PathExtensionContentTypeResolver extends AbstractMappingContentType
 	}
 
 
+	/**
+	 * Whether to only use the registered mappings to look up file extensions, or also refer to
+	 * defaults.
+	 * <p>By default this is set to {@code false}, meaning that defaults are used.
+	 */
+	public void setUseRegisteredExtensionsOnly(boolean useRegisteredExtensionsOnly) {
+		this.useRegisteredExtensionsOnly = useRegisteredExtensionsOnly;
+	}
+
 	/**
 	 * Whether to ignore requests with unknown file extension. Setting this to
 	 * {@code false} results in {@code HttpMediaTypeNotAcceptableException}.
@@ -80,14 +91,16 @@ public class PathExtensionContentTypeResolver extends AbstractMappingContentType
 
 	@Override
 	protected MediaType handleNoMatch(String key) throws NotAcceptableStatusException {
-		Optional<MediaType> mediaType = MediaTypeFactory.getMediaType("file." + key);
-		if (mediaType.isPresent()) {
-			return mediaType.get();
+		if (!this.useRegisteredExtensionsOnly) {
+			Optional<MediaType> mediaType = MediaTypeFactory.getMediaType("file." + key);
+			if (mediaType.isPresent()) {
+				return mediaType.get();
+			}
 		}
-		if (!this.ignoreUnknownExtensions) {
-			throw new NotAcceptableStatusException(getAllMediaTypes());
+		if (this.ignoreUnknownExtensions) {
+			return null;
 		}
-		return null;
+		throw new NotAcceptableStatusException(getAllMediaTypes());
 	}
 
 	/**

spring-webflux/src/main/java/org/springframework/web/reactive/accept/RequestedContentTypeResolverBuilder.java

@@ -93,6 +93,8 @@ public class RequestedContentTypeResolverBuilder {
 
 	private boolean ignoreUnknownPathExtensions = true;
 
+	private Boolean useRegisteredExtensionsOnly;
+
 	private String parameterName = "format";
 
 	private RequestedContentTypeResolver contentTypeResolver;
@@ -152,6 +154,18 @@ public class RequestedContentTypeResolverBuilder {
 		return this;
 	}
 
+	/**
+	 * When {@link #favorPathExtension favorPathExtension} is set, this
+	 * property determines whether to use only registered {@code MediaType} mappings
+	 * to resolve a path extension to a specific MediaType.
+	 * <p>By default this is not set in which case
+	 * {@code PathExtensionContentNegotiationStrategy} will use defaults if available.
+	 */
+	public RequestedContentTypeResolverBuilder useRegisteredExtensionsOnly(boolean useRegisteredExtensionsOnly) {
+		this.useRegisteredExtensionsOnly = useRegisteredExtensionsOnly;
+		return this;
+	}
+
 	/**
 	 * Whether a request parameter ("format" by default) should be used to
 	 * determine the requested media type. For this option to work you must
@@ -211,6 +225,9 @@ public class RequestedContentTypeResolverBuilder {
 		if (this.favorPathExtension) {
 			PathExtensionContentTypeResolver resolver = new PathExtensionContentTypeResolver(this.mediaTypes);
 			resolver.setIgnoreUnknownExtensions(this.ignoreUnknownPathExtensions);
+			if (this.useRegisteredExtensionsOnly != null) {
+				resolver.setUseRegisteredExtensionsOnly(this.useRegisteredExtensionsOnly);
+			}
 			resolvers.add(resolver);
 		}