CompressionFilter.java

/*
 * Copyright LGPL3
 * YES Technology Association
 * http://yestech.org
 *
 * http://www.opensource.org/licenses/lgpl-3.0.html
 */
package org.yestech.lib.web.filter;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.yestech.lib.web.GenericResponseWrapper;
import static org.yestech.lib.web.RequestUtils.*;
import static org.yestech.lib.web.ResponseUtils.*;

import javax.servlet.*;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.util.zip.GZIPOutputStream;

/**
 * Provides compression of responses. Currently only GZip is supported. In the future other compression
 * algorithms will be integrated.
 * <p/>
 * See the filter-mappings.xml entry for the gzip filter for the URL patterns
 * which will be gzipped. At present this includes .jsp, .js and .css.
 * <p/>
 *
 * @author Artie Copeland
 * @version $Revision: $
 */
public class CompressionFilter implements Filter {
    final private static Logger logger = LoggerFactory.getLogger(CompressionFilter.class);

    @Override
    public void init(FilterConfig filterConfig) throws ServletException {
        //To change body of implemented methods use File | Settings | File Templates.
    }

    @Override
    public void doFilter(ServletRequest rawRequest, ServletResponse rawResponse, FilterChain chain) throws IOException, ServletException {
        HttpServletRequest request = (HttpServletRequest) rawRequest;
        HttpServletResponse response = (HttpServletResponse) rawResponse;
        if (!isIncluded(request) && acceptsEncoding(request, "gzip")) {
            // Client accepts zipped content
            if (logger.isDebugEnabled()) {
                logger.debug(request.getRequestURL() + ". Writing with gzip compression");
            }

            // Create a gzip stream
            final ByteArrayOutputStream compressed = new ByteArrayOutputStream();
            final GZIPOutputStream gzout = new GZIPOutputStream(compressed);

            // Handle the request
            final GenericResponseWrapper wrapper = new GenericResponseWrapper(response, gzout);
            chain.doFilter(request, wrapper);
            wrapper.flush();

            gzout.close();

            //return on error or redirect code, because response is already committed
            int statusCode = wrapper.getStatus();
            if (statusCode != HttpServletResponse.SC_OK) {
                return;
            }

            //Saneness checks
            byte[] compressedBytes = compressed.toByteArray();
            boolean shouldGzippedBodyBeZero = shouldGzippedBodyBeZero(compressedBytes, request);
            boolean shouldBodyBeZero = shouldBodyBeZero(request, wrapper.getStatus());
            if (shouldGzippedBodyBeZero || shouldBodyBeZero) {
                compressedBytes = new byte[0];
            }

            // Write the zipped body
            addGzipHeader(response);
            response.setContentLength(compressedBytes.length);


            response.getOutputStream().write(compressedBytes);
        } else {
            // Client does not accept zipped content - don't bother zipping
            if (logger.isDebugEnabled()) {
                logger.debug(request.getRequestURL()
                        + ". Writing without gzip compression because the request does not accept gzip.");
            }
            chain.doFilter(request, response);
        }
    }

    @Override
    public void destroy() {
        //To change body of implemented methods use File | Settings | File Templates.
    }
}