Add ResolvedResource in resource handling chain

Prior to this commit, the resource handling chain and its
`ResourceResolvers` would use specific `Resource` implementations in
order to add resource metadata to the HTTP response. For example,
`VersionedResource` and `EncodedResource` are both adding specific HTTP
response headers.

This commit aims at making this mechanism more stable and reusable,
since the previous implementation would fail in case a resolved resource
would be both a `VersionedResource` wrapping a `EncodedResource` (or the
other way arount). Only one of the specific implementations would
contribute its metadata since the code supporting that in
`ResourceHttpRequestHandler` would only check for `instanceof` tests,
whereas those implementations are acutally delegating calls to
the wrapped resource.

Now both `VersionedResource` and `EncodedResource` have been replaced by
specific implementations of `ResolvedResource`, which directly provides
those HTTP response headers as part of `getResponseHeaders()`.

This commit applies the same changes for the web reactive
implementations and its `ResourceWebHandler`.

Issue: SPR-14264

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

@@ -1,43 +0,0 @@
-/*
- * Copyright 2002-2015 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.servlet.resource;
-
-import org.springframework.core.io.Resource;
-
-/**
- * Interface for a resource descriptor that describes the encoding
- * applied to the entire resource content.
- *
- * <p>This information is required if the client consuming that resource
- * needs additional decoding capabilities to retrieve the resource's content.
- *
- * @author Jeremy Grelle
- * @since 4.1
- * @see <a href="http://tools.ietf.org/html/rfc7231#section-3.1.2.2">HTTP/1.1: Semantics
- * and Content, section 3.1.2.2</a>
- */
-public interface EncodedResource extends Resource {
-
-	/**
-	 * The content coding value, as defined in the IANA registry
-	 * @return the content encoding
-	 * @see <a href="http://tools.ietf.org/html/rfc7231#section-3.1.2.1">HTTP/1.1: Semantics
-	 * and Content, section 3.1.2.1</a>
-	 */
-	String getContentEncoding();
-
-}

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

@@ -22,10 +22,12 @@ import java.io.InputStream;
 import java.net.URI;
 import java.net.URL;
 import java.util.List;
+
 import javax.servlet.http.HttpServletRequest;
 
 import org.springframework.core.io.AbstractResource;
 import org.springframework.core.io.Resource;
+import org.springframework.http.HttpHeaders;
 
 /**
  * A {@code ResourceResolver} that delegates to the chain to locate a resource
@@ -76,7 +78,7 @@ public class GzipResourceResolver extends AbstractResourceResolver {
 	}
 
 
-	private static final class GzippedResource extends AbstractResource implements EncodedResource {
+	private static final class GzippedResource extends AbstractResource implements ResolvedResource {
 
 		private final Resource original;
 
@@ -140,9 +142,19 @@ public class GzipResourceResolver extends AbstractResourceResolver {
 			return this.gzipped.getDescription();
 		}
 
-		public String getContentEncoding() {
-			return "gzip";
+		@Override
+		public HttpHeaders getResponseHeaders() {
+			HttpHeaders headers;
+			if(this.original instanceof ResolvedResource) {
+				headers = ((ResolvedResource) this.original).getResponseHeaders();
+			}
+			else {
+				headers = new HttpHeaders();
+			}
+			headers.add(HttpHeaders.CONTENT_ENCODING, "gzip");
+			return headers;
 		}
+
 	}
 
 }

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

@@ -0,0 +1,27 @@
+package org.springframework.web.servlet.resource;
+
+import org.springframework.core.io.Resource;
+import org.springframework.http.HttpHeaders;
+
+/**
+ * Interface for resources resolved through the
+ * {@link org.springframework.web.servlet.resource.ResourceResolverChain}
+ * that may contribute HTTP response headers as they're served to HTTP clients.
+ *
+ * <p>Some resource implementations, while served by the
+ * {@link org.springframework.web.servlet.resource.ResourceResolverChain} need
+ * to contribute resource metadata as HTTP response headers so that HTTP clients
+ * can interpret them properly.
+ *
+ * @author Brian Clozel
+ * @since 5.0
+ */
+public interface ResolvedResource extends Resource {
+
+	/**
+	 * The HTTP headers to be contributed to the HTTP response
+	 * that serves the current resource.
+	 * @return the HTTP response headers
+	 */
+	HttpHeaders getResponseHeaders();
+}

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

@@ -542,11 +542,10 @@ public class ResourceHttpRequestHandler extends WebContentGenerator
 		if (mediaType != null) {
 			response.setContentType(mediaType.toString());
 		}
-		if (resource instanceof EncodedResource) {
-			response.setHeader(HttpHeaders.CONTENT_ENCODING, ((EncodedResource) resource).getContentEncoding());
-		}
-		if (resource instanceof VersionedResource) {
-			response.setHeader(HttpHeaders.ETAG, "\"" + ((VersionedResource) resource).getVersion() + "\"");
+		if (resource instanceof ResolvedResource) {
+			HttpHeaders resourceHeaders = ((ResolvedResource) resource).getResponseHeaders();
+			resourceHeaders.toSingleValueMap().entrySet()
+					.stream().forEach(entry -> response.setHeader(entry.getKey(), entry.getValue()));
 		}
 		response.setHeader(HttpHeaders.ACCEPT_RANGES, "bytes");
 	}

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

@@ -32,6 +32,7 @@ import javax.servlet.http.HttpServletRequest;
 
 import org.springframework.core.io.AbstractResource;
 import org.springframework.core.io.Resource;
+import org.springframework.http.HttpHeaders;
 import org.springframework.util.AntPathMatcher;
 import org.springframework.util.StringUtils;
 
@@ -238,7 +239,7 @@ public class VersionResourceResolver extends AbstractResourceResolver {
 	}
 
 
-	private class FileNameVersionedResource extends AbstractResource implements VersionedResource {
+	private class FileNameVersionedResource extends AbstractResource implements ResolvedResource {
 
 		private final Resource original;
 
@@ -315,9 +316,18 @@ public class VersionResourceResolver extends AbstractResourceResolver {
 		}
 
 		@Override
-		public String getVersion() {
-			return this.version;
+		public HttpHeaders getResponseHeaders() {
+			HttpHeaders headers;
+			if(this.original instanceof ResolvedResource) {
+				headers = ((ResolvedResource) this.original).getResponseHeaders();
+			}
+			else {
+				headers = new HttpHeaders();
+			}
+			headers.setETag("\"" + this.version + "\"");
+			return headers;
 		}
+
 	}
 
 }

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

@@ -1,33 +0,0 @@
-/*
- * 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.servlet.resource;
-
-import org.springframework.core.io.Resource;
-
-/**
- * Interface for a resource descriptor that describes its version with a
- * version string that can be derived from its content and/or metadata.
- *
- * @author Brian Clozel
- * @since 4.2.5
- * @see VersionResourceResolver
- */
-public interface VersionedResource extends Resource {
-
-	String getVersion();
-
-}