compressionfilter.java

jGossip是一个简单而功能强大的Java论坛软件（消息板）

/*
 * $$Id: CompressionFilter.java,v 1.4 2004/05/30 20:03:56 bel70 Exp $$
 *
 * ***** BEGIN LICENSE BLOCK *****
 * The contents of this file are subject to the Mozilla Public License
 * Version 1.1 (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.mozilla.org/MPL/
 *
 * Software distributed under the License is distributed on an "AS IS"
 * basis, WITHOUT WARRANTY OF ANY KIND, either express or implied. See
 * the License for the specific language governing rights and
 * limitations under the License.
 *
 * The Original Code is JGossip forum code.
 *
 * The Initial Developer of the Original Code is the JResearch, Org.
 * Portions created by the Initial Developer are Copyright (C) 2004
 * the Initial Developer. All Rights Reserved.
 *
 * Contributor(s):
 *              Dmitry Belov <[e-mail]>
 *
 * ***** END LICENSE BLOCK ***** */
package org.jresearch.gossip.filters;

import org.jresearch.filters.CharArrayWrapper;

import org.jresearch.gossip.IConst;
import org.jresearch.gossip.configuration.Configurator;
import org.jresearch.gossip.exception.ConfiguratorException;

import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.io.OutputStream;
import java.io.OutputStreamWriter;

import java.util.zip.GZIPOutputStream;

import javax.servlet.Filter;
import javax.servlet.FilterChain;
import javax.servlet.FilterConfig;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;


/**
 * Filter that compresses output with gzip (assuming that browser supports
 * gzip).
 */
public class CompressionFilter implements Filter {
    public static final String GZIP_NOT_ALLOWED = "GZIP_NOT_ALLOWED";
    private FilterConfig config;

    /**
     * If browser does not support gzip, invoke resource normally. If browser
     * <I>does</I> support gzip, set the Content-Encoding response header and
     * invoke resource with a wrapped response that collects all the output.
     * Extract the output and write it into a gzipped byte array. Finally,
     * write that array to the client's output stream.
     *
     * @param request DOCUMENT ME!
     * @param response DOCUMENT ME!
     * @param chain DOCUMENT ME!
     *
     * @throws ServletException DOCUMENT ME!
     * @throws IOException DOCUMENT ME!
     */
    public void doFilter(ServletRequest request, ServletResponse response,
        FilterChain chain) throws ServletException, IOException {
        HttpServletRequest req = (HttpServletRequest) request;
        HttpServletResponse res = (HttpServletResponse) response;

        try {
            if (!isGzipSupported(req) ||
                    (IConst.VALUES.FALSE.equals(Configurator.getInstance().get(IConst.CONFIG.GZIP_COMPRESS))) ||
                    (req.getParameter(GZIP_NOT_ALLOWED) != null)) {
                // Invoke resource normally.
                chain.doFilter(req, res);
            } else {
                // Tell browser we are sending it gzipped data.
                res.setHeader("Content-Encoding", "gzip");

                // Invoke resource, accumulating output in the wrapper.
                CharArrayWrapper responseWrapper = new CharArrayWrapper(res);
                chain.doFilter(req, responseWrapper);

                // Get character array representing output.
                char[] responseChars = responseWrapper.toCharArray();

                // Make a writer that compresses data and puts
                // it into a byte array.
                ByteArrayOutputStream byteStream = new ByteArrayOutputStream();
                GZIPOutputStream zipOut = new GZIPOutputStream(byteStream);
                OutputStreamWriter tempOut = new OutputStreamWriter(zipOut);

                // Compress original output and put it into byte array.
                tempOut.write(responseChars);

                // Gzip streams must be explicitly closed.
                tempOut.close();

                // Update the Content-Length header.
                res.setContentLength(byteStream.size());

                // Send compressed result to client.
                OutputStream realOut = res.getOutputStream();
                byteStream.writeTo(realOut);
            }
        } catch (ConfiguratorException e) {
            throw new ServletException(e);
        }
    }

    /**
     * Store the FilterConfig object in case subclasses want it.
     *
     * @param config DOCUMENT ME!
     *
     * @throws ServletException DOCUMENT ME!
     */
    public void init(FilterConfig config) throws ServletException {
        this.config = config;
    }

    /**
     * DOCUMENT ME!
     *
     * @return DOCUMENT ME!
     */
    protected FilterConfig getFilterConfig() {
        return (config);
    }

    /**
     * DOCUMENT ME!
     */
    public void destroy() {
    }

    private boolean isGzipSupported(HttpServletRequest req) {
        String browserEncodings = req.getHeader("Accept-Encoding");

        return ((browserEncodings != null) &&
        (browserEncodings.indexOf("gzip") != -1));
    }
}