001/*
002 * Copyright 2002-2019 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.reactive.resource;
018
019import java.util.List;
020
021import org.webjars.WebJarAssetLocator;
022import reactor.core.publisher.Mono;
023
024import org.springframework.core.io.Resource;
025import org.springframework.lang.Nullable;
026import org.springframework.web.server.ServerWebExchange;
027
028/**
029 * A {@code ResourceResolver} that delegates to the chain to locate a resource and then
030 * attempts to find a matching versioned resource contained in a WebJar JAR file.
031 *
032 * <p>This allows WebJars.org users to write version agnostic paths in their templates,
033 * like {@code <script src="/jquery/jquery.min.js"/>}.
034 * This path will be resolved to the unique version {@code <script src="/jquery/1.2.0/jquery.min.js"/>},
035 * which is a better fit for HTTP caching and version management in applications.
036 *
037 * <p>This also resolves resources for version agnostic HTTP requests {@code "GET /jquery/jquery.min.js"}.
038 *
039 * <p>This resolver requires the {@code org.webjars:webjars-locator-core} library
040 * on the classpath and is automatically registered if that library is present.
041 *
042 * @author Rossen Stoyanchev
043 * @author Brian Clozel
044 * @since 5.0
045 * @see <a href="https://www.webjars.org">webjars.org</a>
046 */
047public class WebJarsResourceResolver extends AbstractResourceResolver {
048
049        private static final String WEBJARS_LOCATION = "META-INF/resources/webjars/";
050
051        private static final int WEBJARS_LOCATION_LENGTH = WEBJARS_LOCATION.length();
052
053
054        private final WebJarAssetLocator webJarAssetLocator;
055
056
057        /**
058         * Create a {@code WebJarsResourceResolver} with a default {@code WebJarAssetLocator} instance.
059         */
060        public WebJarsResourceResolver() {
061                this(new WebJarAssetLocator());
062        }
063
064        /**
065         * Create a {@code WebJarsResourceResolver} with a custom {@code WebJarAssetLocator} instance,
066         * e.g. with a custom index.
067         */
068        public WebJarsResourceResolver(WebJarAssetLocator webJarAssetLocator) {
069                this.webJarAssetLocator = webJarAssetLocator;
070        }
071
072
073        @Override
074        protected Mono<Resource> resolveResourceInternal(@Nullable ServerWebExchange exchange,
075                        String requestPath, List<? extends Resource> locations, ResourceResolverChain chain) {
076
077                return chain.resolveResource(exchange, requestPath, locations)
078                                .switchIfEmpty(Mono.defer(() -> {
079                                        String webJarsResourcePath = findWebJarResourcePath(requestPath);
080                                        if (webJarsResourcePath != null) {
081                                                return chain.resolveResource(exchange, webJarsResourcePath, locations);
082                                        }
083                                        else {
084                                                return Mono.empty();
085                                        }
086                                }));
087        }
088
089        @Override
090        protected Mono<String> resolveUrlPathInternal(String resourceUrlPath,
091                        List<? extends Resource> locations, ResourceResolverChain chain) {
092
093                return chain.resolveUrlPath(resourceUrlPath, locations)
094                                .switchIfEmpty(Mono.defer(() -> {
095                                        String webJarResourcePath = findWebJarResourcePath(resourceUrlPath);
096                                        if (webJarResourcePath != null) {
097                                                return chain.resolveUrlPath(webJarResourcePath, locations);
098                                        }
099                                        else {
100                                                return Mono.empty();
101                                        }
102                                }));
103        }
104
105        @Nullable
106        protected String findWebJarResourcePath(String path) {
107                int startOffset = (path.startsWith("/") ? 1 : 0);
108                int endOffset = path.indexOf('/', 1);
109                if (endOffset != -1) {
110                        String webjar = path.substring(startOffset, endOffset);
111                        String partialPath = path.substring(endOffset + 1);
112                        String webJarPath = this.webJarAssetLocator.getFullPathExact(webjar, partialPath);
113                        if (webJarPath != null) {
114                                return webJarPath.substring(WEBJARS_LOCATION_LENGTH);
115                        }
116                }
117                return null;
118        }
119
120}