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

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

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/*
 * Copyright 2002-2014 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
 *
 * http://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.File;
import java.io.IOException;
import java.io.InputStream;
import java.net.URI;
import java.net.URL;
import java.util.List;

import javax.servlet.http.HttpServletRequest;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.springframework.core.io.AbstractResource;
import org.springframework.core.io.Resource;

/**
 * A {@code ResourceResolver} that delegates to the chain to locate a resource
 * and then attempts to find a variation with the ".gz" extension.
 *
 * <p>The resolver gets involved only if the "Accept-Encoding" request header
 * contains the value "gzip" indicating the client accepts gzipped responses.
 *
 * @author Jeremy Grelle
 * @author Rossen Stoyanchev
 * @since 4.1
 */
public class GzipResourceResolver implements ResourceResolver {

    private static final Log logger = LogFactory.getLog(GzipResourceResolver.class);

    @Override
    public Resource resolveResource(HttpServletRequest request, String requestPath, List<Resource> locations,
            ResourceResolverChain chain) {

        Resource resource = chain.resolveResource(request, requestPath, locations);
        if ((resource == null) || !isGzipAccepted(request)) {
            return resource;
        }

        try {
            Resource gzipped = new GzippedResource(resource);
            if (gzipped.exists()) {
                return gzipped;
            }
        } catch (IOException e) {
            logger.trace("No gzipped resource for [" + resource.getFilename() + "]", e);
        }

        return resource;
    }

    private boolean isGzipAccepted(HttpServletRequest request) {
        String value = request.getHeader("Accept-Encoding");
        return ((value != null) && value.toLowerCase().contains("gzip"));
    }

    @Override
    public String getPublicUrlPath(String resourceUrlPath, List<Resource> locations, ResourceResolverChain chain) {
        return chain.resolveUrlPath(resourceUrlPath, locations);
    }

    private static final class GzippedResource extends AbstractResource implements EncodedResource {

        private final Resource original;

        private final Resource gzipped;

        public GzippedResource(Resource original) throws IOException {
            this.original = original;
            this.gzipped = original.createRelative(original.getFilename() + ".gz");
        }

        public InputStream getInputStream() throws IOException {
            return this.gzipped.getInputStream();
        }

        public boolean exists() {
            return this.gzipped.exists();
        }

        public boolean isReadable() {
            return this.gzipped.isReadable();
        }

        public boolean isOpen() {
            return this.gzipped.isOpen();
        }

        public URL getURL() throws IOException {
            return this.gzipped.getURL();
        }

        public URI getURI() throws IOException {
            return this.gzipped.getURI();
        }

        public File getFile() throws IOException {
            return this.gzipped.getFile();
        }

        public long contentLength() throws IOException {
            return this.gzipped.contentLength();
        }

        public long lastModified() throws IOException {
            return this.gzipped.lastModified();
        }

        public Resource createRelative(String relativePath) throws IOException {
            return this.gzipped.createRelative(relativePath);
        }

        public String getFilename() {
            return this.original.getFilename();
        }

        public String getDescription() {
            return this.gzipped.getDescription();
        }

        public String getContentEncoding() {
            return "gzip";
        }
    }

}