org.hd.d.pg2k.webSvr.util
Class CompressionFilter

java.lang.Object
  org.hd.d.pg2k.webSvr.util.CompressionFilter

All Implemented Interfaces:

javax.servlet.Filter

public final class CompressionFilter
extends java.lang.Object
implements javax.servlet.Filter

Implementation of javax.servlet.Filter used to compress the ServletResponse if it is bigger than a threshold.

We might need to modify this to suppress caching for HTTP/1.0 clients (eg by setting Pragma: no-cache and Expires: 0).

Version:

$Revision: 1.8 $, $Date: 2005/08/18 09:30:46 $

Author:

Amy Roh (original), Damon Hart-Davis

GZIP_TOKEN

static final java.lang.String GZIP_TOKEN

Encoding token indicating that GZIP compression is accepted. The test should be case-insensitive and work if the client-supplied token starts with "x-".

See Also:

Constant Field Values

logger

private final WebUtils.ServletLoggerWithFallback logger

Our logger which falls back to System.out if servlet log not available; never null.

statsIDCompression

private final StatsLogger.StatsConfig statsIDCompression

The stats set to which we log HTTP gzip-(un)compressed-transport counts. This is one of three codes for:

• The compression filter is invoked (may only be available in debug modes).
• Not compressable (eg explicitly disabled).
• Compressable (including client browser support, though possibly not compressed if not large enough, etc).

We may enable or disable this logging (etc) from system parameters, but this is nonetheless our unique identifier.

config

private javax.servlet.FilterConfig config

The filter configuration object we are associated with. If this value is null, this filter instance is not currently configured.

overrideAttribute

private java.lang.String overrideAttribute

The name of the application-level attribute to disable compression if Boolean.FALSE, or null.

compressionThreshold

protected int compressionThreshold

The threshold result size below which not to try to compress.

debug

private int debug

Debug level for this filter.

ANTI_DUP_ATTR_NAME

private static final java.lang.String ANTI_DUP_ATTR_NAME

Name of attribute that we use to avoid duplicate application of this filter on one filter chain.

See Also:

Constant Field Values

CompressionFilter

public CompressionFilter()

getFilterConfig

public javax.servlet.FilterConfig getFilterConfig()

setFilterConfig

public void setFilterConfig(javax.servlet.FilterConfig c)

init

public void init(javax.servlet.FilterConfig filterConfig)

Place this filter into service.

Specified by:

init in interface javax.servlet.Filter

Parameters:

filterConfig - The filter configuration object

destroy

public void destroy()

Take this filter out of service.

Specified by:

destroy in interface javax.servlet.Filter

doFilter

public void doFilter(javax.servlet.ServletRequest request,
                     javax.servlet.ServletResponse response,
                     javax.servlet.FilterChain chain)
              throws java.io.IOException,
                     javax.servlet.ServletException

Filters the server operation. The doFilter method of the Filter is called by the container each time a request/response pair is passed through the chain due to a client request for a resource at the end of the chain. The FilterChain passed into this method allows the Filter to pass on the request and response to the next entity in the chain.

This method first examines the request to check whether the client supports compression.

It passes the request and response unaltered if there is no support for compression.

If compression support is available, this filter creates a CompressionServletResponseWrapper object which compresses the content and modifies the header if the content length is big enough. It then invokes the next entity in the chain using the FilterChain object (chain.doFilter()).

Specified by:

doFilter in interface javax.servlet.Filter

Throws:

java.io.IOException

javax.servlet.ServletException