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.config.annotation;
018
019import java.util.ArrayList;
020import java.util.List;
021
022import org.springframework.cache.Cache;
023import org.springframework.cache.concurrent.ConcurrentMapCache;
024import org.springframework.lang.Nullable;
025import org.springframework.util.Assert;
026import org.springframework.util.ClassUtils;
027import org.springframework.web.servlet.resource.CachingResourceResolver;
028import org.springframework.web.servlet.resource.CachingResourceTransformer;
029import org.springframework.web.servlet.resource.CssLinkResourceTransformer;
030import org.springframework.web.servlet.resource.PathResourceResolver;
031import org.springframework.web.servlet.resource.ResourceResolver;
032import org.springframework.web.servlet.resource.ResourceTransformer;
033import org.springframework.web.servlet.resource.VersionResourceResolver;
034import org.springframework.web.servlet.resource.WebJarsResourceResolver;
035
036/**
037 * Assists with the registration of resource resolvers and transformers.
038 *
039 * @author Rossen Stoyanchev
040 * @since 4.1
041 */
042public class ResourceChainRegistration {
043
044        private static final String DEFAULT_CACHE_NAME = "spring-resource-chain-cache";
045
046        private static final boolean isWebJarsAssetLocatorPresent = ClassUtils.isPresent(
047                        "org.webjars.WebJarAssetLocator", ResourceChainRegistration.class.getClassLoader());
048
049
050        private final List<ResourceResolver> resolvers = new ArrayList<>(4);
051
052        private final List<ResourceTransformer> transformers = new ArrayList<>(4);
053
054        private boolean hasVersionResolver;
055
056        private boolean hasPathResolver;
057
058        private boolean hasCssLinkTransformer;
059
060        private boolean hasWebjarsResolver;
061
062
063        public ResourceChainRegistration(boolean cacheResources) {
064                this(cacheResources, (cacheResources ? new ConcurrentMapCache(DEFAULT_CACHE_NAME) : null));
065        }
066
067        public ResourceChainRegistration(boolean cacheResources, @Nullable Cache cache) {
068                Assert.isTrue(!cacheResources || cache != null, "'cache' is required when cacheResources=true");
069                if (cacheResources) {
070                        this.resolvers.add(new CachingResourceResolver(cache));
071                        this.transformers.add(new CachingResourceTransformer(cache));
072                }
073        }
074
075
076        /**
077         * Add a resource resolver to the chain.
078         * @param resolver the resolver to add
079         * @return the current instance for chained method invocation
080         */
081        public ResourceChainRegistration addResolver(ResourceResolver resolver) {
082                Assert.notNull(resolver, "The provided ResourceResolver should not be null");
083                this.resolvers.add(resolver);
084                if (resolver instanceof VersionResourceResolver) {
085                        this.hasVersionResolver = true;
086                }
087                else if (resolver instanceof PathResourceResolver) {
088                        this.hasPathResolver = true;
089                }
090                else if (resolver instanceof WebJarsResourceResolver) {
091                        this.hasWebjarsResolver = true;
092                }
093                return this;
094        }
095
096        /**
097         * Add a resource transformer to the chain.
098         * @param transformer the transformer to add
099         * @return the current instance for chained method invocation
100         */
101        public ResourceChainRegistration addTransformer(ResourceTransformer transformer) {
102                Assert.notNull(transformer, "The provided ResourceTransformer should not be null");
103                this.transformers.add(transformer);
104                if (transformer instanceof CssLinkResourceTransformer) {
105                        this.hasCssLinkTransformer = true;
106                }
107                return this;
108        }
109
110        protected List<ResourceResolver> getResourceResolvers() {
111                if (!this.hasPathResolver) {
112                        List<ResourceResolver> result = new ArrayList<>(this.resolvers);
113                        if (isWebJarsAssetLocatorPresent && !this.hasWebjarsResolver) {
114                                result.add(new WebJarsResourceResolver());
115                        }
116                        result.add(new PathResourceResolver());
117                        return result;
118                }
119                return this.resolvers;
120        }
121
122        protected List<ResourceTransformer> getResourceTransformers() {
123                if (this.hasVersionResolver && !this.hasCssLinkTransformer) {
124                        List<ResourceTransformer> result = new ArrayList<>(this.transformers);
125                        boolean hasTransformers = !this.transformers.isEmpty();
126                        boolean hasCaching = hasTransformers && this.transformers.get(0) instanceof CachingResourceTransformer;
127                        result.add(hasCaching ? 1 : 0, new CssLinkResourceTransformer());
128                        return result;
129                }
130                return this.transformers;
131        }
132
133}