Precompression hates me

[Thomas May]

I'm using GWT with tomcat 6 and 7. I've tried writing a filter to forward things if the requested content + ".gz" exists. That works, except for the fact that the requestDispatcher will commit the request and set the content type to application/x-gzip

How do I fix this?

Here is my current code

package com.ca.myapp.filters;

import java.io.IOException;
import java.net.MalformedURLException;
import java.util.Map;
import java.util.concurrent.ConcurrentHashMap;
import javax.servlet.Filter;
import javax.servlet.FilterChain;
import javax.servlet.FilterConfig;
import javax.servlet.ServletContext;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

public class GzipFilter implements Filter
{
	private static Map<String, String> compressionMap = new ConcurrentHashMap<String, String>();
	private static ServletContext serverletContext;
	
	@Override
	public void init(FilterConfig filterConfig) throws ServletException
	{
		serverletContext = filterConfig.getServletContext();
	}

	@Override
	public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException
	{
		HttpServletResponse hsr = (HttpServletResponse)response;
		String oldContentType = hsr.getContentType();
		if(supportsGzip((HttpServletRequest)request))
		{
			modifyRequestURI((HttpServletRequest)request, (HttpServletResponse)response);
		}
		chain.doFilter(request, hsr);
		hsr.setContentType(oldContentType);
	}

	private boolean supportsGzip(HttpServletRequest httpServletRequest)
	{
		boolean accepts = false;
		String encoding = httpServletRequest.getHeader("Accept-Encoding");
		if (null != encoding && encoding.indexOf("gzip") > -1)
		{
			accepts = true;
		}
		return accepts;
	}

	private boolean modifyRequestURI(HttpServletRequest httpServletRequest, HttpServletResponse response)
	{
		String requestUri = httpServletRequest.getRequestURI();
		String newUri = compressionMap.get(requestUri);
		if (newUri == null)
		{
			newUri = "";
			try
			{
				if (serverletContext.getResource(requestUri + ".gz") != null)
				{
					newUri = requestUri + ".gz";
				}
			}
			catch (MalformedURLException ex)
			{
			}
			compressionMap.put(requestUri, newUri);
		}
		if (!"".equals(newUri)) // no staticly compressed file exists
		{
			try
			{
				response.setHeader("Content-Encoding", "gzip");
				httpServletRequest.getRequestDispatcher(newUri).forward(httpServletRequest, response);
			}
			catch (ServletException ex)
			{
				return false;
			}
			catch (IOException ex)
			{
				return false;
			}
			return true;
		}
		return false;
	}
	
	@Override
	public void destroy()
	{
	}
}

[William Brogden]

The Tomcat default web.xml includes the following:

    <mime-mapping>
        <extension>gz</extension>
        <mime-type>application/x-gzip</mime-type>
    </mime-mapping>

which, as I understand it, controls the way the default servlet sets content type when serving resources.

Bill