org.springframework.web.servlet.resource.DefaultResourceResolverChain.java Source code

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Here is the source code for org.springframework.web.servlet.resource.DefaultResourceResolverChain.java

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/*
 * 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.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 ResourceResolverChain}.
 *
 * @author Rossen Stoyanchev
 * @since 4.1
 */
class DefaultResourceResolverChain implements ResourceResolverChain {

    @Nullable
    private final ResourceResolver resolver;

    @Nullable
    private final ResourceResolverChain nextChain;

    public DefaultResourceResolverChain(@Nullable List<? extends ResourceResolver> resolvers) {
        resolvers = (resolvers != null ? resolvers : Collections.emptyList());
        DefaultResourceResolverChain chain = initChain(new ArrayList<>(resolvers));
        this.resolver = chain.resolver;
        this.nextChain = chain.nextChain;
    }

    private static DefaultResourceResolverChain initChain(ArrayList<? extends ResourceResolver> resolvers) {
        DefaultResourceResolverChain chain = new DefaultResourceResolverChain(null, null);
        ListIterator<? extends ResourceResolver> it = resolvers.listIterator(resolvers.size());
        while (it.hasPrevious()) {
            chain = new DefaultResourceResolverChain(it.previous(), chain);
        }
        return chain;
    }

    private DefaultResourceResolverChain(@Nullable ResourceResolver resolver,
            @Nullable ResourceResolverChain chain) {
        Assert.isTrue((resolver == null && chain == null) || (resolver != null && chain != null),
                "Both resolver and resolver chain must be null, or neither is");
        this.resolver = resolver;
        this.nextChain = chain;
    }

    @Override
    @Nullable
    public Resource resolveResource(@Nullable HttpServletRequest request, String requestPath,
            List<? extends Resource> locations) {

        return (this.resolver != null && this.nextChain != null
                ? this.resolver.resolveResource(request, requestPath, locations, this.nextChain)
                : null);
    }

    @Override
    @Nullable
    public String resolveUrlPath(String resourcePath, List<? extends Resource> locations) {
        return (this.resolver != null && this.nextChain != null
                ? this.resolver.resolveUrlPath(resourcePath, locations, this.nextChain)
                : null);
    }

}