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-web/src/main/java/org/springframework/http/MediaTypeFactory.java

@@ -104,11 +104,9 @@ public class MediaTypeFactory {
 	 * @return the corresponding media type, or {@code null} if none found
 	 */
 	public static Optional<MediaType> getMediaType(Resource resource) {
-		if (resource == null) {
-			return Optional.empty();
-		}
-		String filename = resource.getFilename();
-		return (filename != null ? getMediaType(filename) : Optional.empty());
+		return Optional.ofNullable(resource)
+				.map(Resource::getFilename)
+				.flatMap(MediaTypeFactory::getMediaType);
 	}
 
 	/**
@@ -117,8 +115,7 @@ public class MediaTypeFactory {
 	 * @return the corresponding media type, or {@code null} if none found
 	 */
 	public static Optional<MediaType> getMediaType(String filename) {
-		List<MediaType> mediaTypes = getMediaTypes(filename);
-		return (!mediaTypes.isEmpty() ? Optional.of(mediaTypes.get(0)) : Optional.empty());
+		return getMediaTypes(filename).stream().findFirst();
 	}
 
 	/**

spring-web/src/main/java/org/springframework/web/accept/ContentNegotiationManager.java

@@ -143,7 +143,9 @@ public class ContentNegotiationManager implements ContentNegotiationStrategy, Me
 	 * <p>At startup this method returns extensions explicitly registered with
 	 * either {@link PathExtensionContentNegotiationStrategy} or
 	 * {@link ParameterContentNegotiationStrategy}. At runtime if there is a
-	 * "path extension" strategy, the list of extensions may
+	 * "path extension" strategy and its
+	 * {@link PathExtensionContentNegotiationStrategy#setUseRegisteredExtensionsOnly(boolean)
+	 * useRegisteredExtensionsOnly} property is set to "false", the list of extensions may
 	 * increase as file extensions are resolved via
 	 * {@link org.springframework.http.MediaTypeFactory} and cached.
 	 */

spring-web/src/main/java/org/springframework/web/accept/ContentNegotiationManagerFactoryBean.java

@@ -100,6 +100,8 @@ public class ContentNegotiationManagerFactoryBean
 
 	private boolean ignoreUnknownPathExtensions = true;
 
+	private Boolean useRegisteredExtensionsOnly;
+
 	private String parameterName = "format";
 
 	private ContentNegotiationStrategy defaultNegotiationStrategy;
@@ -175,10 +177,27 @@ public class ContentNegotiationManagerFactoryBean
 	}
 
 	/**
-	 * @deprecated as 5.0, in favor of {@link MediaTypeFactory}, which has no JAF dependency.
+	 * @deprecated as of 5.0, in favor of {@link #setUseRegisteredExtensionsOnly(boolean)}, which
+	 * has reverse behavior.
 	 */
 	@Deprecated
 	public void setUseJaf(boolean useJaf) {
+		setUseRegisteredExtensionsOnly(!useJaf);
+	}
+
+	/**
+	 * When {@link #setFavorPathExtension 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 void setUseRegisteredExtensionsOnly(boolean useRegisteredExtensionsOnly) {
+		this.useRegisteredExtensionsOnly = useRegisteredExtensionsOnly;
+	}
+
+	private boolean useRegisteredExtensionsOnly() {
+		return (this.useRegisteredExtensionsOnly != null && this.useRegisteredExtensionsOnly);
 	}
 
 	/**
@@ -244,7 +263,7 @@ public class ContentNegotiationManagerFactoryBean
 
 		if (this.favorPathExtension) {
 			PathExtensionContentNegotiationStrategy strategy;
-			if (this.servletContext != null) {
+			if (this.servletContext != null && !useRegisteredExtensionsOnly()) {
 				strategy = new ServletPathExtensionContentNegotiationStrategy(
 						this.servletContext, this.mediaTypes);
 			}
@@ -252,6 +271,9 @@ public class ContentNegotiationManagerFactoryBean
 				strategy = new PathExtensionContentNegotiationStrategy(this.mediaTypes);
 			}
 			strategy.setIgnoreUnknownExtensions(this.ignoreUnknownPathExtensions);
+			if (this.useRegisteredExtensionsOnly != null) {
+				strategy.setUseRegisteredExtensionsOnly(this.useRegisteredExtensionsOnly);
+			}
 			strategies.add(strategy);
 		}
 

spring-web/src/main/java/org/springframework/web/accept/PathExtensionContentNegotiationStrategy.java

@@ -51,6 +51,8 @@ public class PathExtensionContentNegotiationStrategy extends AbstractMappingCont
 
 	private UrlPathHelper urlPathHelper = new UrlPathHelper();
 
+	private boolean useRegisteredExtensionsOnly = false;
+
 	private boolean ignoreUnknownExtensions = true;
 
 
@@ -81,10 +83,20 @@ public class PathExtensionContentNegotiationStrategy extends AbstractMappingCont
 	}
 
 	/**
-	 * @deprecated as 5.0, in favor of {@link MediaTypeFactory}, which has no JAF dependency.
+	 * @deprecated as of 5.0, in favor of {@link #setUseRegisteredExtensionsOnly(boolean)}.
 	 */
 	@Deprecated
 	public void setUseJaf(boolean useJaf) {
+		setUseRegisteredExtensionsOnly(!useJaf);
+	}
+
+	/**
+	 * 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;
 	}
 
 	/**
@@ -113,9 +125,11 @@ public class PathExtensionContentNegotiationStrategy extends AbstractMappingCont
 	protected MediaType handleNoMatch(NativeWebRequest webRequest, String extension)
 			throws HttpMediaTypeNotAcceptableException {
 
-		Optional<MediaType> mediaType = MediaTypeFactory.getMediaType("file." + extension);
-		if (mediaType.isPresent()) {
-			return mediaType.get();
+		if (!this.useRegisteredExtensionsOnly) {
+			Optional<MediaType> mediaType = MediaTypeFactory.getMediaType("file." + extension);
+			if (mediaType.isPresent()) {
+				return mediaType.get();
+			}
 		}
 		if (this.ignoreUnknownExtensions) {
 			return null;

spring-web/src/main/java/org/springframework/web/accept/ServletPathExtensionContentNegotiationStrategy.java

@@ -93,6 +93,7 @@ public class ServletPathExtensionContentNegotiationStrategy extends PathExtensio
 	 * @return the MediaType for the extension or {@code null}.
 	 * @since 4.3
 	 */
+	@Override
 	public MediaType getMediaTypeForResource(Resource resource) {
 		MediaType mediaType = null;
 		if (this.servletContext != null) {