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 - 
  • CacheControlFilter
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  • HttpFilter

Available since OmniFaces 1.7

This filter will control the cache-related headers of the response. Cache-related headers have a major impact on performance (network bandwidth and server load) and user experience (up to date content and non-expired views).

By default, when no initialization parameters are specified, the filter will instruct the client (generally, the webbrowser) to not cache the response. This is recommended on dynamic pages with stateful forms with a javax.faces.ViewState hidden field. If such a page were cached, and the enduser navigates to it by webbrowser's back button, and then re-submits it, then the enduser would face a ViewExpiredException.

However, on stateless resources, caching the response would be beneficial. Set the expire time to the same time as you'd like to use as refresh interval of the resource, which can be 10 seconds (to avoid F5-madness on resources which are subject to quick changes), but also minutes or even hours, days or weeks. For example, a list of links, a news page, a JS/CSS/image file, etc.

Any sane server and client adheres the following rules as to caching:

  • When the enduser performs page-to-page navigation, or when the enduser selects URL in address bar and presses enter key again, while the resource is cached, then the client will just load it from the cache without hitting the server in any way.
  • Or when the cache is expired, or when the enduser does a soft-refresh by pressing refresh button or F5 key, then:
    • When the ETag or Last-Modified header is present on cached resource, then the client will perform a so-called conditional GET request with If-None-Match or If-Modified-Since headers. If the server responds with HTTP status 304 ("not modified") along with the updated cache-related headers, then the client will keep the resource in cache and expand its expire time based on the headers. Note: ETag takes precedence over Last-Modified when both are present and consequently If-None-Match takes precedence over If-Modified-Since when both are present.
    • When those headers are not present, then the behavior is the same as during a hard-refresh.
  • Or when the resource is not cached, or when the enduser does a hard-refresh by pressing Ctrl key along with refresh button or F5, then the webbrowser will perform a fresh new request and purge any cached resource.

Important notice: this filter automatically skips JSF resources, such as the ones served by <h:outputScript>, <h:outputStylesheet>, @ResourceDependency, etc. Their cache-related headers are namely already controlled by the ResourceHandler implementation. In Mojarra and MyFaces, the default expiration time is 1 week (604800000 milliseconds), which can be configured by a web.xml context parameter with the following name and a value in milliseconds, e.g. 3628800000 for 6 weeks:

  • Mojarra: com.sun.faces.defaultResourceMaxAge
  • MyFaces: org.apache.myfaces.RESOURCE_MAX_TIME_EXPIRES

It would not make sense to control their cache-related headers with this filter as they would be overridden anyway.

Configuration

This filter supports the expires initialization parameter which must be a number between 0 and 999999999 with optionally the 'w', 'd', 'h', 'm' or 's' suffix standing for respectively 'week', 'day', 'hour', 'minute' and 'second'. For example: '6w' is 6 weeks. The default suffix is 's'. So, when the suffix is omitted, it's treated as seconds. For example: '86400' is 86400 seconds, which is effectively equal to '86400s', '1440m', '24h' and '1d'.

Imagine that you've the following resources:

  • All /forum/* pages: cache 10 seconds.
  • All *.pdf and *.zip files: cache 2 days.
  • All other pages: no cache.

Then you can configure the filter as follows (filter name is fully free to your choice, but keep it sensible):

<filter>
    <filter-name>noCache</filter-name>
    <filter-class>org.omnifaces.filter.CacheControlFilter</filter-class>
</filter>
<filter>
    <filter-name>cache10seconds</filter-name>
    <filter-class>org.omnifaces.filter.CacheControlFilter</filter-class>
    <init-param>
        <param-name>expires</param-name>
        <param-value>10s</param-value>
    </init-param>
</filter>
<filter>
    <filter-name>cache2days</filter-name>
    <filter-class>org.omnifaces.filter.CacheControlFilter</filter-class>
    <init-param>
        <param-name>expires</param-name>
        <param-value>2d</param-value>
    </init-param>
</filter>

<filter-mapping>
    <filter-name>noCache</filter-name>
    <url-pattern>/*</url-pattern>
</filter-mapping>
<filter-mapping>
    <filter-name>cache10seconds</filter-name>
    <url-pattern>/forum/*</url-pattern>
</filter-mapping>
<filter-mapping>
    <filter-name>cache2days</filter-name>
    <url-pattern>*.pdf</url-pattern>
    <url-pattern>*.zip</url-pattern>
</filter-mapping>

Note: put the more specific URL patterns in the end of filter mappings. Due to the way how filters work, there's unfortunately no simple way to skip the filter on /* when e.g. *.pdf is matched. You can always map the no cache filter specifically to FacesServlet if you intend to disable caching on all JSF pages. Here's an example assuming that you've configured the FacesServlet with a servlet name of facesServlet:

<filter-mapping>
    <filter-name>noCache</filter-name>
    <servlet-name>facesServlet</servlet-name>
</filter-mapping>

Actual headers

If the expires init param is set with a value which represents a time larger than 0 seconds, then the following headers will be set:

  • Cache-Control: public,max-age=[expiration time in seconds],must-revalidate
  • Expires: [expiration date of now plus expiration time in seconds]

If the expires init param is absent, or set with a value which represents a time equal to 0 seconds, then the following headers will be set:

  • Cache-Control: no-cache,no-store,must-revalidate
  • Expires: [expiration date of 0]
  • Pragma: no-cache

JSF development stage

To speed up development, caching by this filter is disabled when JSF project stage is set to Development as per Servlets.isFacesDevelopment(javax.servlet.ServletContext).

Demo

The CacheControlFilter is also configured on this showcase application. You can see it by no-cache related headers being set on JSF pages throughout the showcase application and by the presence of the filter in stacktraces of showcase pages demonstrating some exceptions.