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

+/*
+ * 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

+/*
+ * 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

+/*
+ * 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

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

spring-web-reactive/src/test/java/org/springframework/web/reactive/accept/HeaderContentTypeResolverTests.java

+/*
+ * 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.net.URI;
+import java.net.URISyntaxException;
+import java.util.List;
+
+import org.junit.Before;
+import org.junit.Test;
+
+import org.springframework.http.HttpMethod;
+import org.springframework.http.MediaType;
+import org.springframework.http.server.reactive.MockServerHttpRequest;
+import org.springframework.http.server.reactive.MockServerHttpResponse;
+import org.springframework.http.server.reactive.ServerHttpRequest;
+import org.springframework.web.HttpMediaTypeNotAcceptableException;
+import org.springframework.web.server.ServerWebExchange;
+import org.springframework.web.server.adapter.DefaultServerWebExchange;
+import org.springframework.web.server.session.WebSessionManager;
+
+import static org.junit.Assert.assertEquals;
+import static org.mockito.Mockito.mock;
+
+/**
+ * Unit tests for {@link HeaderContentTypeResolver}.
+ *
+ * @author Rossen Stoyanchev
+ */
+public class HeaderContentTypeResolverTests {
+
+	private HeaderContentTypeResolver resolver;
+
+
+	@Before
+	public void setup() {
+		this.resolver = new HeaderContentTypeResolver();
+	}
+
+
+	@Test
+	public void resolveMediaTypes() throws Exception {
+		ServerWebExchange exchange = createExchange("text/plain; q=0.5, text/html, text/x-dvi; q=0.8, text/x-c");
+		List<MediaType> mediaTypes = this.resolver.resolveMediaTypes(exchange);
+
+		assertEquals(4, mediaTypes.size());
+		assertEquals("text/html", mediaTypes.get(0).toString());
+		assertEquals("text/x-c", mediaTypes.get(1).toString());
+		assertEquals("text/x-dvi;q=0.8", mediaTypes.get(2).toString());
+		assertEquals("text/plain;q=0.5", mediaTypes.get(3).toString());
+	}
+
+	@Test(expected=HttpMediaTypeNotAcceptableException.class)
+	public void resolveMediaTypesParseError() throws Exception {
+		ServerWebExchange exchange = createExchange("textplain; q=0.5");
+		this.resolver.resolveMediaTypes(exchange);
+	}
+
+
+	private ServerWebExchange createExchange(String accept) throws URISyntaxException {
+		ServerHttpRequest request = new MockServerHttpRequest(HttpMethod.GET, new URI("/"));
+		if (accept != null) {
+			request.getHeaders().add("Accept", accept);
+		}
+		WebSessionManager sessionManager = mock(WebSessionManager.class);
+		return new DefaultServerWebExchange(request, new MockServerHttpResponse(), sessionManager);
+	}
+
+}