Extract base interface for VersionStrategy

This change splits out a base VersionPathStrategy interface that
focuses on where in the URL path the version is embedded.

Author: rstoyanchev

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

@@ -6,6 +6,7 @@
 import org.apache.commons.logging.Log;
 import org.apache.commons.logging.LogFactory;
 
+import org.springframework.util.Assert;
 import org.springframework.util.StringUtils;
 
 /**
@@ -20,73 +21,106 @@
  * version string.
  *
  * @author Brian Clozel
+ * @author Rossen Stoyanchev
  * @since 4.1
  */
 public abstract class AbstractVersionStrategy implements VersionStrategy {
 
-	private static final Pattern pattern = Pattern.compile("-(\\S*)\\.");
-
 	protected final Log logger = LogFactory.getLog(getClass());
 
-	/**
-	 * Extracts a version string from the request path, as a suffix in the resource
-	 * file name.
-	 * @param requestPath the request path to extract the version string from
-	 * @return a version string or an empty string if none was found
-	 */
-	protected String extractVersionFromFilename(String requestPath) {
-		Matcher matcher = pattern.matcher(requestPath);
-		if (matcher.find()) {
-			String match = matcher.group(1);
-			return match.contains("-") ? match.substring(match.lastIndexOf("-") + 1) : match;
-		}
-		else {
-			return "";
-		}
+	private final VersionPathStrategy pathStrategy;
+
+
+	protected AbstractVersionStrategy(VersionPathStrategy pathStrategy) {
+		Assert.notNull(pathStrategy, "'pathStrategy' is required");
+		this.pathStrategy = pathStrategy;
 	}
 
-	/**
-	 * Deletes the given candidate version string from the request path.
-	 * The version string should be a suffix in the resource file name.
-	 */
-	protected String deleteVersionFromFilename(String requestPath, String candidateVersion) {
-		return StringUtils.delete(requestPath, "-" + candidateVersion);
+
+	public VersionPathStrategy getVersionPathStrategy() {
+		return this.pathStrategy;
 	}
 
-	/**
-	 * Adds the given version string to the baseUrl, as a file name suffix.
-	 */
-	protected String addVersionToFilename(String baseUrl, String version) {
-		String baseFilename = StringUtils.stripFilenameExtension(baseUrl);
-		String extension = StringUtils.getFilenameExtension(baseUrl);
-		return baseFilename + "-" + version + "." + extension;
+
+	@Override
+	public String extractVersion(String requestPath) {
+		return this.pathStrategy.extractVersion(requestPath);
 	}
 
-	/**
-	 * Extracts a version string from the request path, as a prefix in the request path.
-	 * @param requestPath the request path to extract the version string from
-	 * @return a version string or an empty string if none was found
-	 */
-	protected String extractVersionAsPrefix(String requestPath, String prefix) {
-		if (requestPath.startsWith(prefix)) {
-			return prefix;
-		}
-		return "";
+	@Override
+	public String removeVersion(String requestPath, String version) {
+		return this.pathStrategy.removeVersion(requestPath, version);
+	}
+
+	@Override
+	public String addVersion(String requestPath, String version) {
+		return this.pathStrategy.addVersion(requestPath, version);
 	}
 
+
 	/**
-	 * Deletes the given candidate version string from the request path.
-	 * The version string should be a prefix in the request path.
+	 * A prefix-based {@code VersionPathStrategy},
+	 * e.g. {@code "{version}/path/foo.js"}.
 	 */
-	protected String deleteVersionAsPrefix(String requestPath, String version) {
-		return requestPath.substring(version.length());
+	protected static class PrefixVersionPathStrategy implements VersionPathStrategy {
+
+		private final String prefix;
+
+
+		public PrefixVersionPathStrategy(String version) {
+			Assert.hasText(version, "'version' is required and must not be empty");
+			this.prefix = version;
+		}
+
+		@Override
+		public String extractVersion(String requestPath) {
+			return (requestPath.startsWith(this.prefix) ? this.prefix : null);
+		}
+
+		@Override
+		public String removeVersion(String requestPath, String version) {
+			return requestPath.substring(this.prefix.length());
+		}
+
+		@Override
+		public String addVersion(String path, String version) {
+			return (this.prefix.endsWith("/") || path.startsWith("/") ? this.prefix + path : this.prefix + "/" + path);
+		}
+
 	}
 
 	/**
-	 * Adds the given version string to the baseUrl, as a prefix in the request path.
+	 * File name-based {@code VersionPathStrategy},
+	 * e.g. {@code "path/foo-{version}.css"}.
 	 */
-	protected String addVersionAsPrefix(String baseUrl, String version) {
-		return version + baseUrl;
+	protected static class FileNameVersionPathStrategy implements VersionPathStrategy {
+
+		private static final Pattern pattern = Pattern.compile("-(\\S*)\\.");
+
+
+		@Override
+		public String extractVersion(String requestPath) {
+			Matcher matcher = pattern.matcher(requestPath);
+			if (matcher.find()) {
+				String match = matcher.group(1);
+				return match.contains("-") ? match.substring(match.lastIndexOf("-") + 1) : match;
+			}
+			else {
+				return null;
+			}
+		}
+
+		@Override
+		public String removeVersion(String requestPath, String version) {
+			return StringUtils.delete(requestPath, "-" + version);
+		}
+
+		@Override
+		public String addVersion(String requestPath, String version) {
+			String baseFilename = StringUtils.stripFilenameExtension(requestPath);
+			String extension = StringUtils.getFilenameExtension(requestPath);
+			return baseFilename + "-" + version + "." + extension;
+		}
 	}
 
 }

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

@@ -0,0 +1,53 @@
+/*
+ * Copyright 2002-2014 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 java.io.IOException;
+
+import org.springframework.core.io.Resource;
+import org.springframework.util.DigestUtils;
+import org.springframework.util.FileCopyUtils;
+
+/**
+ * A {@code VersionStrategy} that calculates an Hex MD5 hashes from the content
+ * of the resource and appends it to the file name, e.g.
+ * {@code "styles/main-e36d2e05253c6c7085a91522ce43a0b4.css"}.
+ *
+ * @author Brian Clozel
+ * @author Rossen Stoyanchev
+ * @since 4.1
+ * @see VersionResourceResolver
+ */
+public class ContentVersionStrategy extends AbstractVersionStrategy {
+
+
+	public ContentVersionStrategy() {
+		super(new FileNameVersionPathStrategy());
+	}
+
+
+	@Override
+	public String getResourceVersion(Resource resource) {
+		try {
+			byte[] content = FileCopyUtils.copyToByteArray(resource.getInputStream());
+			return DigestUtils.md5DigestAsHex(content);
+		}
+		catch (IOException ex) {
+			throw new IllegalStateException("Failed to calculate hash for resource [" + resource + "]", ex);
+		}
+	}
+
+}

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

@@ -15,28 +15,18 @@
  */
 package org.springframework.web.servlet.resource;
 
-import java.util.List;
-import java.util.concurrent.Callable;
-
 import org.springframework.core.io.Resource;
-import org.springframework.util.Assert;
 
 /**
- * A {@code VersionStrategy} that handles unique, static, application-wide version strings
- * as prefixes in the request path.
- *
- * <p>Enables inserting a unique and static version String (e.g. reduced SHA, version name,
- * release date) at the beginning of resource paths so that when a new version of the application
- * is released, clients are forced to reload application resources.
+ * A {@code VersionStrategy} that relies on a fixed version applied as a request
+ * path prefix, e.g. reduced SHA, version name, release date, etc.
  *
- * <p>This is useful when changing resource names is not an option (e.g. when
- * using JavaScript module loaders). If that's not the case, the use of
- * {@link ContentBasedVersionStrategy} provides more optimal performance since
- * version is generated on a per-resource basis: only actually modified resources are reloaded
- * by the client.
+ * <p>This is useful for example when {@link ContentVersionStrategy} cannot be
+ * used such as when using JavaScript module loaders which are in charge of
+ * loading the JavaScript resources and need to know their relative paths.
  *
  * @author Brian Clozel
- * @author Sam Brannen
+ * @author Rossen Stoyanchev
  * @since 4.1
  * @see VersionResourceResolver
  */
@@ -46,44 +36,17 @@ public class FixedVersionStrategy extends AbstractVersionStrategy {
 
 	/**
 	 * Create a new FixedVersionStrategy with the given version string.
-	 * @param fixedVersion the fixed version string to use
-	 */
-	public FixedVersionStrategy(String fixedVersion) {
-		Assert.hasText(fixedVersion, "version must not be null or empty");
-		this.version = fixedVersion.endsWith("/") ? fixedVersion : fixedVersion + "/";
-	}
-
-	/**
-	 * Create a new FixedVersionStrategy and get the version string to use by
-	 * calling the given {@code Callable} instance.
+	 * @param version the fixed version string to use
 	 */
-	public FixedVersionStrategy(Callable<String> versionInitializer) throws Exception {
-		String fixedVersion = versionInitializer.call();
-		Assert.hasText(fixedVersion, "version must not be null or empty");
-		this.version = fixedVersion.endsWith("/") ? fixedVersion : fixedVersion + "/";
-	}
-
-	@Override
-	public String extractVersionFromPath(String requestPath) {
-
-		return extractVersionAsPrefix(requestPath, this.version);
-	}
-
-	@Override
-	public String deleteVersionFromPath(String requestPath, String candidateVersion) {
-		return deleteVersionAsPrefix(requestPath, candidateVersion);
+	public FixedVersionStrategy(String version) {
+		super(new PrefixVersionPathStrategy(version));
+		this.version = version;
 	}
 
-	@Override
-	public boolean resourceVersionMatches(Resource baseResource, String candidateVersion) {
-		return this.version.equals(candidateVersion);
-	}
 
 	@Override
-	public String addVersionToUrl(String baseUrl, List<? extends Resource> locations,
-			ResourceResolverChain chain) {
-
-		return addVersionAsPrefix(baseUrl, this.version);
+	public String getResourceVersion(Resource resource) {
+		return this.version;
 	}
 
 }