net.sf.ehcache.constructs.web.filter
Class SimpleCachingHeadersPageCachingFilter

java.lang.Object
  net.sf.ehcache.constructs.web.filter.Filter
      net.sf.ehcache.constructs.web.filter.CachingFilter
          net.sf.ehcache.constructs.web.filter.SimplePageCachingFilter
              net.sf.ehcache.constructs.web.filter.SimpleCachingHeadersPageCachingFilter

All Implemented Interfaces:

javax.servlet.Filter

public class SimpleCachingHeadersPageCachingFilter
extends SimplePageCachingFilter

This Filter extends SimplePageCachingFilter, adding support for the HTTP cache headers: ETag, Last-Modified and Expires.

Because browsers and other HTTP clients have the expiry information returned in the response headers, they do not even need to request the page again. Even once the local browser copy has expired, the browser will do a conditional GET.

So why would you ever want to use SimplePageCachingFilter, which does not set these headers? Because in some caching scenarios you may wish to remove a page before its natural expiry. Consider a scenario where a web page shows dynamic data. Under Ehcache the Element can be removed at any time. However if a browser is holding expiry information, those browsers will have to wait until the expiry time before getting updated. The caching in this scenario is more about defraying server load rather than minimising browser calls.

Author:

Craig Andrews, Greg Luck

See Also:

SimplePageCachingFilter

Field Summary

static String

NAME The name of the filter.

Fields inherited from class net.sf.ehcache.constructs.web.filter.SimplePageCachingFilter

DEFAULT_CACHE_NAME

Fields inherited from class net.sf.ehcache.constructs.web.filter.CachingFilter

blockingCache, cacheName

Fields inherited from class net.sf.ehcache.constructs.web.filter.Filter

exceptionsToLogDifferently, filterConfig, NO_FILTER, suppressStackTraces

Constructor Summary

SimpleCachingHeadersPageCachingFilter()

Method Summary

protected PageInfo	buildPage(javax.servlet.http.HttpServletRequest request, javax.servlet.http.HttpServletResponse response, javax.servlet.FilterChain chain) Builds the PageInfo object by passing the request along the filter chain
protected long	calculateTimeToLiveMilliseconds() Get the time to live for a page, in milliseconds
protected HttpDateFormatter	getHttpDateFormatter()
protected void	writeResponse(javax.servlet.http.HttpServletRequest request, javax.servlet.http.HttpServletResponse response, PageInfo pageInfo) Writes the response from a PageInfo object.

Methods inherited from class net.sf.ehcache.constructs.web.filter.SimplePageCachingFilter

calculateKey, getCacheManager, getCacheName

Methods inherited from class net.sf.ehcache.constructs.web.filter.CachingFilter

buildPageInfo, checkNoReentry, doDestroy, doFilter, doInit, setCacheNameIfAnyConfigured, setContentType, setCookies, setHeaders, setStatus, writeContent

Methods inherited from class net.sf.ehcache.constructs.web.filter.Filter

acceptsEncoding, acceptsGzipEncoding, destroy, doFilter, filterNotDisabled, getFilterConfig, init, logRequestHeaders, processInitParams

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Detail

NAME

public static final String NAME

The name of the filter. This should match a cache name in ehcache.xml

See Also:

Constant Field Values

Constructor Detail

SimpleCachingHeadersPageCachingFilter

public SimpleCachingHeadersPageCachingFilter()

Method Detail

buildPage

protected PageInfo buildPage(javax.servlet.http.HttpServletRequest request,
                             javax.servlet.http.HttpServletResponse response,
                             javax.servlet.FilterChain chain)
                      throws AlreadyGzippedException,
                             Exception

Builds the PageInfo object by passing the request along the filter chain

The following headers are set:

• Last-Modified
• Expires
• Cache-Control
• ETag

Any of these headers aleady set in the response are ignored, and new ones generated. To control your own caching headers, use SimplePageCachingFilter.

Overrides:

buildPage in class CachingFilter

Parameters:

request -

response -

chain -

Returns:

a Serializable value object for the page or page fragment

Throws:

AlreadyGzippedException - if an attempt is made to double gzip the body

Exception

getHttpDateFormatter

protected final HttpDateFormatter getHttpDateFormatter()

Returns:

A lazily created HttpDateFormatter instance scoped to this filter

writeResponse

protected void writeResponse(javax.servlet.http.HttpServletRequest request,
                             javax.servlet.http.HttpServletResponse response,
                             PageInfo pageInfo)
                      throws IOException,
                             DataFormatException,
                             ResponseHeadersNotModifiableException

Writes the response from a PageInfo object. This method actually performs the conditional GET and returns 304 if not modified, short-circuiting the normal writeResponse.

Indeed, if the short cicruit does not occur it calls the super method.

Overrides:

writeResponse in class CachingFilter

Throws:

IOException

DataFormatException

ResponseHeadersNotModifiableException

calculateTimeToLiveMilliseconds

protected long calculateTimeToLiveMilliseconds()

Get the time to live for a page, in milliseconds

Returns:

time to live in milliseconds