compressionfilter.java

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package org.roller.presentation.filters;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;

import java.io.ByteArrayOutputStream;
import java.io.IOException;
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).
 *  <P>
 *  Taken from More Servlets and JavaServer Pages
 *  from Prentice Hall and Sun Microsystems Press,
 *  http://www.moreservlets.com/.
 *  &copy; 2002 Marty Hall; may be freely used or adapted.
 * 
 * @web.filter name="PageGzipFilter"
 * *web.filter-mapping url-pattern="/page/*"
 */

public class CompressionFilter implements Filter
{
    private static Log mLogger =
        LogFactory.getFactory().getInstance(CompressionFilter.class);
        
	/** 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.
	 */
	public void doFilter(
		ServletRequest request,
		ServletResponse response,
		FilterChain chain)
		throws ServletException, IOException
	{
		HttpServletRequest req = (HttpServletRequest) request;
		HttpServletResponse res = (HttpServletResponse) response;
		if (!isGzipSupported(req))
		{
			// 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.
            ByteArrayResponseWrapper responseWrapper =
                new ByteArrayResponseWrapper(response);
            
			chain.doFilter(req, responseWrapper);

            ByteArrayOutputStream outputStream = responseWrapper.getByteArrayOutputStream();

			// Get character array representing output.
            if (mLogger.isDebugEnabled())
            {
                mLogger.debug("Pre-zip size:" + outputStream.size());
            }
            
			// Make a writer that compresses data and puts
			// it into a byte array.
			ByteArrayOutputStream byteStream = new ByteArrayOutputStream();
			GZIPOutputStream zipOut = new GZIPOutputStream(byteStream);

			// Compress original output and put it into byte array.
            zipOut.write(responseWrapper.getByteArrayOutputStream().toByteArray());

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

            if (mLogger.isDebugEnabled())
            {
                mLogger.debug("Gzip size:" + byteStream.size());
            }
            
            // Update the Content-Length header.
			res.setContentLength(byteStream.size());

            ByteArrayOutputStreamWrapper newOut =
                (ByteArrayOutputStreamWrapper) responseWrapper.getOutputStream();
            newOut.clear();
            newOut.setFinallized();
        
            /* now force close of OutputStream */
            newOut.write(byteStream.toByteArray());
            newOut.close();            
		}
	}

	/** Store the FilterConfig object in case subclasses
	 *  want it.
	 */
	public void init(FilterConfig config) throws ServletException
	{
	}

	public void destroy()
	{
	}

	private boolean isGzipSupported(HttpServletRequest req)
	{
		String browserEncodings = req.getHeader("Accept-Encoding");
		return (
			(browserEncodings != null)
				&& (browserEncodings.indexOf("gzip") != -1));
	}
 
}