Java tutorial
/* * Copyright 2002-2017 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 * * https://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.ByteArrayOutputStream; import java.io.IOException; import java.io.StringWriter; import java.nio.charset.Charset; import java.nio.charset.StandardCharsets; import java.util.Arrays; import java.util.Collection; import java.util.Collections; import java.util.Scanner; import javax.servlet.http.HttpServletRequest; import org.apache.commons.logging.Log; import org.apache.commons.logging.LogFactory; import org.springframework.core.io.Resource; import org.springframework.lang.Nullable; import org.springframework.util.DigestUtils; import org.springframework.util.FileCopyUtils; import org.springframework.util.StringUtils; /** * A {@link ResourceTransformer} implementation that helps handling resources * within HTML5 AppCache manifests for HTML5 offline applications. * * <p>This transformer: * <ul> * <li>modifies links to match the public URL paths that should be exposed to clients, * using configured {@code ResourceResolver} strategies * <li>appends a comment in the manifest, containing a Hash (e.g. "# Hash: 9de0f09ed7caf84e885f1f0f11c7e326"), * thus changing the content of the manifest in order to trigger an appcache reload in the browser. * </ul> * * <p>All files that have the ".appcache" file extension, or the extension given in the constructor, * will be transformed by this class. This hash is computed using the content of the appcache manifest * and the content of the linked resources; so changing a resource linked in the manifest * or the manifest itself should invalidate the browser cache. * * <p>In order to serve manifest files with the proper {@code "text/manifest"} content type, * it is required to configure it with * {@code contentNegotiationConfigurer.mediaType("appcache", MediaType.valueOf("text/manifest")} * in a {@code WebMvcConfigurer}. * * @author Brian Clozel * @since 4.1 * @see <a href="https://html.spec.whatwg.org/multipage/browsers.html#offline">HTML5 offline applications spec</a> */ public class AppCacheManifestTransformer extends ResourceTransformerSupport { private static final Collection<String> MANIFEST_SECTION_HEADERS = Arrays.asList("CACHE MANIFEST", "NETWORK:", "FALLBACK:", "CACHE:"); private static final String MANIFEST_HEADER = "CACHE MANIFEST"; private static final String CACHE_HEADER = "CACHE:"; private static final Charset DEFAULT_CHARSET = StandardCharsets.UTF_8; private static final Log logger = LogFactory.getLog(AppCacheManifestTransformer.class); private final String fileExtension; /** * Create an AppCacheResourceTransformer that transforms files with extension ".appcache". */ public AppCacheManifestTransformer() { this("appcache"); } /** * Create an AppCacheResourceTransformer that transforms files with the extension * given as a parameter. */ public AppCacheManifestTransformer(String fileExtension) { this.fileExtension = fileExtension; } @Override public Resource transform(HttpServletRequest request, Resource resource, ResourceTransformerChain chain) throws IOException { resource = chain.transform(request, resource); if (!this.fileExtension.equals(StringUtils.getFilenameExtension(resource.getFilename()))) { return resource; } byte[] bytes = FileCopyUtils.copyToByteArray(resource.getInputStream()); String content = new String(bytes, DEFAULT_CHARSET); if (!content.startsWith(MANIFEST_HEADER)) { if (logger.isTraceEnabled()) { logger.trace("Skipping " + resource + ": Manifest does not start with 'CACHE MANIFEST'"); } return resource; } @SuppressWarnings("resource") Scanner scanner = new Scanner(content); LineInfo previous = null; LineAggregator aggregator = new LineAggregator(resource, content); while (scanner.hasNext()) { String line = scanner.nextLine(); LineInfo current = new LineInfo(line, previous); LineOutput lineOutput = processLine(current, request, resource, chain); aggregator.add(lineOutput); previous = current; } return aggregator.createResource(); } private static byte[] getResourceBytes(Resource resource) throws IOException { return FileCopyUtils.copyToByteArray(resource.getInputStream()); } private LineOutput processLine(LineInfo info, HttpServletRequest request, Resource resource, ResourceTransformerChain transformerChain) { if (!info.isLink()) { return new LineOutput(info.getLine(), null); } Resource appCacheResource = transformerChain.getResolverChain().resolveResource(null, info.getLine(), Collections.singletonList(resource)); String path = info.getLine(); String absolutePath = toAbsolutePath(path, request); String newPath = resolveUrlPath(absolutePath, request, resource, transformerChain); return new LineOutput((newPath != null ? newPath : path), appCacheResource); } private static class LineInfo { private final String line; private final boolean cacheSection; private final boolean link; public LineInfo(String line, @Nullable LineInfo previous) { this.line = line; this.cacheSection = initCacheSectionFlag(line, previous); this.link = iniLinkFlag(line, this.cacheSection); } private static boolean initCacheSectionFlag(String line, @Nullable LineInfo previousLine) { if (MANIFEST_SECTION_HEADERS.contains(line.trim())) { return line.trim().equals(CACHE_HEADER); } else if (previousLine != null) { return previousLine.isCacheSection(); } throw new IllegalStateException("Manifest does not start with " + MANIFEST_HEADER + ": " + line); } private static boolean iniLinkFlag(String line, boolean isCacheSection) { return (isCacheSection && StringUtils.hasText(line) && !line.startsWith("#") && !line.startsWith("//") && !hasScheme(line)); } private static boolean hasScheme(String line) { int index = line.indexOf(':'); return (line.startsWith("//") || (index > 0 && !line.substring(0, index).contains("/"))); } public String getLine() { return this.line; } public boolean isCacheSection() { return this.cacheSection; } public boolean isLink() { return this.link; } } private static class LineOutput { private final String line; @Nullable private final Resource resource; public LineOutput(String line, @Nullable Resource resource) { this.line = line; this.resource = resource; } public String getLine() { return this.line; } @Nullable public Resource getResource() { return this.resource; } } private static class LineAggregator { private final StringWriter writer = new StringWriter(); private final ByteArrayOutputStream baos; private final Resource resource; public LineAggregator(Resource resource, String content) { this.resource = resource; this.baos = new ByteArrayOutputStream(content.length()); } public void add(LineOutput lineOutput) throws IOException { this.writer.write(lineOutput.getLine() + "\n"); byte[] bytes = (lineOutput.getResource() != null ? DigestUtils.md5Digest(getResourceBytes(lineOutput.getResource())) : lineOutput.getLine().getBytes(DEFAULT_CHARSET)); this.baos.write(bytes); } public TransformedResource createResource() { String hash = DigestUtils.md5DigestAsHex(this.baos.toByteArray()); this.writer.write("\n" + "# Hash: " + hash); byte[] bytes = this.writer.toString().getBytes(DEFAULT_CHARSET); return new TransformedResource(this.resource, bytes); } } }