001/*
002 * Copyright 2002-2017 the original author or authors.
003 *
004 * Licensed under the Apache License, Version 2.0 (the "License");
005 * you may not use this file except in compliance with the License.
006 * You may obtain a copy of the License at
007 *
008 *      https://www.apache.org/licenses/LICENSE-2.0
009 *
010 * Unless required by applicable law or agreed to in writing, software
011 * distributed under the License is distributed on an "AS IS" BASIS,
012 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
013 * See the License for the specific language governing permissions and
014 * limitations under the License.
015 */
016
017package org.springframework.web.servlet.resource;
018
019import java.util.List;
020
021import javax.servlet.http.HttpServletRequest;
022
023import org.webjars.WebJarAssetLocator;
024
025import org.springframework.core.io.Resource;
026
027/**
028 * A {@code ResourceResolver} that delegates to the chain to locate a resource and then
029 * attempts to find a matching versioned resource contained in a WebJar JAR file.
030 *
031 * <p>This allows WebJars.org users to write version agnostic paths in their templates,
032 * like {@code <script src="/jquery/jquery.min.js"/>}.
033 * This path will be resolved to the unique version {@code <script src="/jquery/1.2.0/jquery.min.js"/>},
034 * which is a better fit for HTTP caching and version management in applications.
035 *
036 * <p>This also resolves resources for version agnostic HTTP requests {@code "GET /jquery/jquery.min.js"}.
037 *
038 * <p>This resolver requires the "org.webjars:webjars-locator" library on classpath,
039 * and is automatically registered if that library is present.
040 *
041 * @author Brian Clozel
042 * @since 4.2
043 * @see org.springframework.web.servlet.config.annotation.ResourceChainRegistration
044 * @see <a href="https://www.webjars.org">webjars.org</a>
045 */
046public class WebJarsResourceResolver extends AbstractResourceResolver {
047
048        private final static String WEBJARS_LOCATION = "META-INF/resources/webjars/";
049
050        private final static int WEBJARS_LOCATION_LENGTH = WEBJARS_LOCATION.length();
051
052
053        private final WebJarAssetLocator webJarAssetLocator;
054
055
056        /**
057         * Create a {@code WebJarsResourceResolver} with a default {@code WebJarAssetLocator} instance.
058         */
059        public WebJarsResourceResolver() {
060                this(new WebJarAssetLocator());
061        }
062
063        /**
064         * Create a {@code WebJarsResourceResolver} with a custom {@code WebJarAssetLocator} instance,
065         * e.g. with a custom index.
066         * @since 4.3
067         */
068        public WebJarsResourceResolver(WebJarAssetLocator webJarAssetLocator) {
069                this.webJarAssetLocator = webJarAssetLocator;
070        }
071
072
073        @Override
074        protected Resource resolveResourceInternal(HttpServletRequest request, String requestPath,
075                        List<? extends Resource> locations, ResourceResolverChain chain) {
076
077                Resource resolved = chain.resolveResource(request, requestPath, locations);
078                if (resolved == null) {
079                        String webJarResourcePath = findWebJarResourcePath(requestPath);
080                        if (webJarResourcePath != null) {
081                                return chain.resolveResource(request, webJarResourcePath, locations);
082                        }
083                }
084                return resolved;
085        }
086
087        @Override
088        protected String resolveUrlPathInternal(String resourceUrlPath,
089                        List<? extends Resource> locations, ResourceResolverChain chain) {
090
091                String path = chain.resolveUrlPath(resourceUrlPath, locations);
092                if (path == null) {
093                        String webJarResourcePath = findWebJarResourcePath(resourceUrlPath);
094                        if (webJarResourcePath != null) {
095                                return chain.resolveUrlPath(webJarResourcePath, locations);
096                        }
097                }
098                return path;
099        }
100
101        protected String findWebJarResourcePath(String path) {
102                int startOffset = (path.startsWith("/") ? 1 : 0);
103                int endOffset = path.indexOf('/', 1);
104                if (endOffset != -1) {
105                        String webjar = path.substring(startOffset, endOffset);
106                        String partialPath = path.substring(endOffset + 1);
107                        String webJarPath = webJarAssetLocator.getFullPathExact(webjar, partialPath);
108                        if (webJarPath != null) {
109                                return webJarPath.substring(WEBJARS_LOCATION_LENGTH);
110                        }
111                }
112                return null;
113        }
114
115}