package org.realityforge.gwt.cache_filter;

import java.io.File;
import java.io.IOException;
import javax.servlet.FilterChain;
import javax.servlet.RequestDispatcher;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
import javax.servlet.annotation.WebFilter;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

/**
 * Filter to redirect all files to their corresponding .gz file, if it exists, and serve
 * it with the proper encoding / content type. Works best if called after GWTCacheControlFilter
 */
@WebFilter( filterName = "GWTGzipControlFilter" )
public class GWTGzipControlFilter
  extends AbstractFilter
{
  private static final String GZIP_EXTENSION = ".gz";

  @Override
  public void doFilter( final ServletRequest servletRequest,
                        final ServletResponse servletResponse,
                        final FilterChain filterChain )
    throws IOException, ServletException
  {
    final HttpServletRequest request = (HttpServletRequest) servletRequest;
    final HttpServletResponse response = (HttpServletResponse) servletResponse;

    if ( !acceptsGzip( request ) )
    {
      filterChain.doFilter( request, response );
    }
    else
    {
      final String resourcePath = request.getServletPath();
      final String realPath = request.getServletContext().getRealPath( resourcePath );
      final File file = null == realPath ? null : new File( realPath );
      if ( null == file ||
           resourcePath.endsWith( GZIP_EXTENSION ) ||
           !file.exists() ||
           file.isDirectory() )
      {
        filterChain.doFilter( request, response );
      }
      else
      {
        final String gzippedPath = realPath + GZIP_EXTENSION;
        final File gzippedFile = new File( gzippedPath );

        if ( !gzippedFile.exists() || gzippedFile.isDirectory() )
        {
          filterChain.doFilter( request, servletResponse );
        }
        else
        {
          final RequestDispatcher dispatcher =
            request.getServletContext().getRequestDispatcher( resourcePath + GZIP_EXTENSION );
          response.setHeader( "Content-Encoding", "gzip" );
          dispatcher.include( request, response );
        }
      }
    }
  }

  public static boolean acceptsGzip( final HttpServletRequest request )
  {
    final String header = request.getHeader( "Accept-Encoding" );
    return null != header && header.contains( "gzip" );
  }
}

package org.realityforge.gwt.cache_filter;

import java.io.File;
import java.io.IOException;
import javax.servlet.FilterChain;
import javax.servlet.RequestDispatcher;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
import javax.servlet.annotation.WebFilter;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

/**
 * Filter to redirect all files to their corresponding .gz file, if it exists, and serve
 * it with the proper encoding / content type. Works best if called after GWTCacheControlFilter
 */
@WebFilter( filterName = "GWTGzipControlFilter" )
public class GWTGzipControlFilter
  extends AbstractFilter
{
  private static final String GZIP_EXTENSION = ".gz";

  @Override
  public void doFilter( final ServletRequest servletRequest,
                        final ServletResponse servletResponse,
                        final FilterChain filterChain )
    throws IOException, ServletException
  {
    final HttpServletRequest request = (HttpServletRequest) servletRequest;
    final HttpServletResponse response = (HttpServletResponse) servletResponse;

    if ( !acceptsGzip( request ) )
    {
      filterChain.doFilter( request, response );
    }
    else
    {
      final String resourcePath = request.getServletPath();
      final String realPath = request.getServletContext().getRealPath( resourcePath );
      final File file = null == realPath ? null : new File( realPath );
      if ( null == file ||
           resourcePath.endsWith( GZIP_EXTENSION ) ||
           !file.exists() ||
           file.isDirectory() )
      {
        filterChain.doFilter( request, response );
      }
      else
      {
        final String gzippedPath = realPath + GZIP_EXTENSION;
        final File gzippedFile = new File( gzippedPath );

        if ( !gzippedFile.exists() || gzippedFile.isDirectory() )
        {
          filterChain.doFilter( request, servletResponse );
        }
        else
        {
          final RequestDispatcher dispatcher =
            request.getServletContext().getRequestDispatcher( resourcePath + GZIP_EXTENSION );
          response.setHeader( "Content-Encoding", "gzip" );
          dispatcher.include( request, response );
        }
      }
    }
  }

  private boolean acceptsGzip( final HttpServletRequest request )
  {
    final String header = request.getHeader( "Accept-Encoding" );
    return null != header && header.contains( "gzip" );
  }
}

Make acceptsGzip into a private method