Add ContentTypeResolver strategy

A starting point for an alternative to the existing
ContentNegotiationStrategy but for use with ServerWebExchange.

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

@@ -0,0 +1,42 @@
+/*
+ * Copyright 2002-2016 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.springframework.web.reactive.accept;
+
+import java.util.List;
+
+import org.springframework.http.MediaType;
+import org.springframework.web.HttpMediaTypeNotAcceptableException;
+import org.springframework.web.server.ServerWebExchange;
+
+/**
+ *
+ * @author Rossen Stoyanchev
+ */
+public interface ContentTypeResolver {
+
+	/**
+	 * Resolve the given request to a list of requested media types. The returned
+	 * list is ordered by specificity first and by quality parameter second.
+	 *
+	 * @param exchange the current exchange
+	 * @return the requested media types or an empty list
+	 *
+	 * @throws HttpMediaTypeNotAcceptableException if the requested media
+	 * types cannot be parsed
+	 */
+	List<MediaType> resolveMediaTypes(ServerWebExchange exchange) throws HttpMediaTypeNotAcceptableException;
+
+}

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

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+/*
+ * Copyright 2002-2016 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.springframework.web.reactive.accept;
+
+import java.util.List;
+
+import org.springframework.http.MediaType;
+
+/**
+ * An extension of {@link ContentTypeResolver} for a resolver that uses file
+ * extensions and can expose file extension mappings.
+ *
+ * @author Rossen Stoyanchev
+ */
+public interface FileExtensionContentTypeResolver extends ContentTypeResolver {
+
+	/**
+	 * Resolve the given media type to a list of path extensions.
+	 *
+	 * @param mediaType the media type to resolve
+	 * @return a list of extensions or an empty list, never {@code null}
+	 */
+	List<String> getFileExtensions(MediaType mediaType);
+
+	/**
+	 * Return all registered file extensions.
+	 * @return a list of extensions or an empty list, never {@code null}
+	 */
+	List<String> getAllFileExtensions();
+
+}

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

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+/*
+ * Copyright 2002-2016 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.springframework.web.reactive.accept;
+
+import java.util.List;
+
+import org.springframework.http.InvalidMediaTypeException;
+import org.springframework.http.MediaType;
+import org.springframework.web.HttpMediaTypeNotAcceptableException;
+import org.springframework.web.server.ServerWebExchange;
+
+/**
+ * A {@link ContentTypeResolver} that checks the 'Accept' request header.
+ *
+ * @author Rossen Stoyanchev
+ */
+public class HeaderContentTypeResolver implements ContentTypeResolver {
+
+	@Override
+	public List<MediaType> resolveMediaTypes(ServerWebExchange exchange)
+			throws HttpMediaTypeNotAcceptableException {
+
+		try {
+			List<MediaType> mediaTypes = exchange.getRequest().getHeaders().getAccept();
+			MediaType.sortBySpecificityAndQuality(mediaTypes);
+			return mediaTypes;
+		}
+		catch (InvalidMediaTypeException ex) {
+			String value = exchange.getRequest().getHeaders().getFirst("Accept");
+			throw new HttpMediaTypeNotAcceptableException(
+					"Could not parse 'Accept' header [" + value + "]: " + ex.getMessage());
+		}
+	}
+}

spring-web-reactive/src/main/java/org/springframework/web/reactive/accept/package-info.java

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+/**
+ * This package provides support for various strategies to resolve the requested
+ * content type for a given request.
+ */
+package org.springframework.web.reactive.accept;