Support HTTP range requests in MVC Controllers

Prior to this commit, HTTP Range requests were only supported by the
ResourceHttpRequestHandler when serving static resources.

This commit improves the `HttpEntityMethodProcessor` and
the `RequestResponseBodyMethodProcessor`. They now extract
`ResourceRegion`s from the `Resource` instance returned by the
Controller and let the Resource-related message converters
handle the writing of the resource (including partial writes).

Controller methods can now handle Range requests for
return types that extend Resource or HttpEntity:

    @RequestMapping("/example/video.mp4")
    public Resource handler() { }

    @RequestMapping("/example/video.mp4")
    public HttpEntity<Resource> handler() { }

Issue: SPR-15789, SPR-13834

spring-webmvc/src/main/java/org/springframework/web/servlet/config/AnnotationDrivenBeanDefinitionParser.java

@@ -44,6 +44,7 @@ import org.springframework.http.MediaType;
 import org.springframework.http.converter.ByteArrayHttpMessageConverter;
 import org.springframework.http.converter.HttpMessageConverter;
 import org.springframework.http.converter.ResourceHttpMessageConverter;
+import org.springframework.http.converter.ResourceRegionHttpMessageConverter;
 import org.springframework.http.converter.StringHttpMessageConverter;
 import org.springframework.http.converter.cbor.MappingJackson2CborHttpMessageConverter;
 import org.springframework.http.converter.feed.AtomFeedHttpMessageConverter;
@@ -579,6 +580,7 @@ class AnnotationDrivenBeanDefinitionParser implements BeanDefinitionParser {
 			messageConverters.add(stringConverterDef);
 
 			messageConverters.add(createConverterDefinition(ResourceHttpMessageConverter.class, source));
+			messageConverters.add(createConverterDefinition(ResourceRegionHttpMessageConverter.class, source));
 			messageConverters.add(createConverterDefinition(SourceHttpMessageConverter.class, source));
 			messageConverters.add(createConverterDefinition(AllEncompassingFormHttpMessageConverter.class, source));
 

spring-webmvc/src/main/java/org/springframework/web/servlet/config/annotation/WebMvcConfigurationSupport.java

@@ -41,6 +41,7 @@ import org.springframework.http.MediaType;
 import org.springframework.http.converter.ByteArrayHttpMessageConverter;
 import org.springframework.http.converter.HttpMessageConverter;
 import org.springframework.http.converter.ResourceHttpMessageConverter;
+import org.springframework.http.converter.ResourceRegionHttpMessageConverter;
 import org.springframework.http.converter.StringHttpMessageConverter;
 import org.springframework.http.converter.cbor.MappingJackson2CborHttpMessageConverter;
 import org.springframework.http.converter.feed.AtomFeedHttpMessageConverter;
@@ -790,6 +791,7 @@ public class WebMvcConfigurationSupport implements ApplicationContextAware, Serv
 		messageConverters.add(new ByteArrayHttpMessageConverter());
 		messageConverters.add(stringConverter);
 		messageConverters.add(new ResourceHttpMessageConverter());
+		messageConverters.add(new ResourceRegionHttpMessageConverter());
 		messageConverters.add(new SourceHttpMessageConverter<>());
 		messageConverters.add(new AllEncompassingFormHttpMessageConverter());
 

spring-webmvc/src/main/java/org/springframework/web/servlet/mvc/method/annotation/AbstractMessageConverterMethodProcessor.java

@@ -30,10 +30,15 @@ import javax.servlet.http.HttpServletRequest;
 import javax.servlet.http.HttpServletResponse;
 
 import org.springframework.core.MethodParameter;
+import org.springframework.core.ParameterizedTypeReference;
 import org.springframework.core.ResolvableType;
+import org.springframework.core.io.Resource;
+import org.springframework.core.io.support.ResourceRegion;
 import org.springframework.http.HttpEntity;
 import org.springframework.http.HttpHeaders;
 import org.springframework.http.HttpOutputMessage;
+import org.springframework.http.HttpRange;
+import org.springframework.http.HttpStatus;
 import org.springframework.http.MediaType;
 import org.springframework.http.converter.GenericHttpMessageConverter;
 import org.springframework.http.converter.HttpMessageConverter;
@@ -75,6 +80,9 @@ public abstract class AbstractMessageConverterMethodProcessor extends AbstractMe
 
 	private static final MediaType MEDIA_TYPE_APPLICATION = new MediaType("application");
 
+	private static final Type RESOURCE_REGION_LIST_TYPE =
+			new ParameterizedTypeReference<List<ResourceRegion>>() { }.getType();
+
 
 	private static final UrlPathHelper decodingUrlPathHelper = new UrlPathHelper();
 
@@ -183,6 +191,24 @@ public abstract class AbstractMessageConverterMethodProcessor extends AbstractMe
 			valueType = getReturnValueType(outputValue, returnType);
 			declaredType = getGenericType(returnType);
 		}
+		
+		if (isResourceType(value, returnType)) {
+			outputMessage.getHeaders().set(HttpHeaders.ACCEPT_RANGES, "bytes");
+			if (value != null && inputMessage.getHeaders().getFirst(HttpHeaders.RANGE) != null) {
+				Resource resource = (Resource) value;
+				try {
+					List<HttpRange> httpRanges = inputMessage.getHeaders().getRange();
+					outputMessage.getServletResponse().setStatus(HttpStatus.PARTIAL_CONTENT.value());
+					outputValue = HttpRange.toResourceRegions(httpRanges, resource);
+					valueType = outputValue.getClass();
+					declaredType = RESOURCE_REGION_LIST_TYPE;
+				}
+				catch (IllegalArgumentException ex) {
+					outputMessage.getHeaders().set(HttpHeaders.CONTENT_RANGE, "bytes */" + resource.contentLength());
+					outputMessage.getServletResponse().setStatus(HttpStatus.REQUESTED_RANGE_NOT_SATISFIABLE.value());
+				}
+			}
+		}
 
 		HttpServletRequest request = inputMessage.getServletRequest();
 		List<MediaType> requestedMediaTypes = getAcceptableMediaTypes(request);
@@ -266,6 +292,13 @@ public abstract class AbstractMessageConverterMethodProcessor extends AbstractMe
 		return (value != null ? value.getClass() : returnType.getParameterType());
 	}
 
+	/**
+	 * Return whether the returned value or the declared return type extend {@link Resource}
+	 */
+	protected boolean isResourceType(@Nullable Object value, MethodParameter returnType) {
+		return Resource.class.isAssignableFrom(value != null ? value.getClass() : returnType.getParameterType());
+	}
+
 	/**
 	 * Return the generic type of the {@code returnType} (or of the nested type
 	 * if it is an {@link HttpEntity}).

spring-webmvc/src/main/java/org/springframework/web/servlet/resource/ResourceHttpRequestHandler.java

@@ -387,14 +387,8 @@ public class ResourceHttpRequestHandler extends WebContentGenerator
 			try {
 				List<HttpRange> httpRanges = inputMessage.getHeaders().getRange();
 				response.setStatus(HttpServletResponse.SC_PARTIAL_CONTENT);
-				if (httpRanges.size() == 1) {
-					ResourceRegion resourceRegion = httpRanges.get(0).toResourceRegion(resource);
-					this.resourceRegionHttpMessageConverter.write(resourceRegion, mediaType, outputMessage);
-				}
-				else {
 					this.resourceRegionHttpMessageConverter.write(
 							HttpRange.toResourceRegions(httpRanges, resource), mediaType, outputMessage);
-				}
 			}
 			catch (IllegalArgumentException ex) {
 				response.setHeader("Content-Range", "bytes */" + resource.contentLength());