Java tutorial
/* * Copyright 2002-2018 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.IOException; import java.util.ArrayList; import java.util.Collections; import java.util.List; import java.util.ListIterator; import javax.servlet.http.HttpServletRequest; import org.springframework.core.io.Resource; import org.springframework.lang.Nullable; import org.springframework.util.Assert; /** * Default immutable implementation of {@link ResourceTransformerChain}. * * @author Rossen Stoyanchev * @since 4.1 */ class DefaultResourceTransformerChain implements ResourceTransformerChain { private final ResourceResolverChain resolverChain; @Nullable private final ResourceTransformer transformer; @Nullable private final ResourceTransformerChain nextChain; public DefaultResourceTransformerChain(ResourceResolverChain resolverChain, @Nullable List<ResourceTransformer> transformers) { Assert.notNull(resolverChain, "ResourceResolverChain is required"); this.resolverChain = resolverChain; transformers = (transformers != null ? transformers : Collections.emptyList()); DefaultResourceTransformerChain chain = initTransformerChain(resolverChain, new ArrayList<>(transformers)); this.transformer = chain.transformer; this.nextChain = chain.nextChain; } private DefaultResourceTransformerChain initTransformerChain(ResourceResolverChain resolverChain, ArrayList<ResourceTransformer> transformers) { DefaultResourceTransformerChain chain = new DefaultResourceTransformerChain(resolverChain, null, null); ListIterator<? extends ResourceTransformer> it = transformers.listIterator(transformers.size()); while (it.hasPrevious()) { chain = new DefaultResourceTransformerChain(resolverChain, it.previous(), chain); } return chain; } public DefaultResourceTransformerChain(ResourceResolverChain resolverChain, @Nullable ResourceTransformer transformer, @Nullable ResourceTransformerChain chain) { Assert.isTrue((transformer == null && chain == null) || (transformer != null && chain != null), "Both transformer and transformer chain must be null, or neither is"); this.resolverChain = resolverChain; this.transformer = transformer; this.nextChain = chain; } public ResourceResolverChain getResolverChain() { return this.resolverChain; } @Override public Resource transform(HttpServletRequest request, Resource resource) throws IOException { return (this.transformer != null && this.nextChain != null ? this.transformer.transform(request, resource, this.nextChain) : resource); } }