OmniFaces Showcase

The GzipResponseFilter will apply GZIP compression on responses whenever applicable. GZIP will greatly reduce the response size when applied on character based responses like HTML, CSS and JS, on average it can save up to ~70% of bandwidth.

While GZIP is normally to be configured in the servlet container (e.g. <Context compression="on"> in Tomcat, or <property name="compression" value="on"> in Glassfish), this filter allows a servlet container independent way of configuring GZIP compression and also allows enabling GZIP compression anyway on 3rd party hosts where you have no control over servlet container configuration.

Installation

To get it to run, map this filter on the desired <url-pattern> or maybe even on the <servlet-name> of the FacesServlet. A Filter is by default dispatched on REQUEST only, you might want to explicitly add the ERROR dispatcher to get it to run on error pages as well.

<filter>
    <filter-name>gzipResponseFilter</filter-name>
    <filter-class>org.omnifaces.filter.GzipResponseFilter</filter-class>
</filter>
<filter-mapping>
    <filter-name>gzipResponseFilter</filter-name>
    <url-pattern>/*</url-pattern>
    <dispatcher>REQUEST</dispatcher>
    <dispatcher>ERROR</dispatcher>
</filter-mapping>

Mapping on /* may be too global as some types of requests (comet, long polling, etc) cannot be gzipped. In that case, consider mapping it to the exact <servlet-name> of the FacesServlet in the same web.xml.

<filter>
    <filter-name>gzipResponseFilter</filter-name>
    <filter-class>org.omnifaces.filter.GzipResponseFilter</filter-class>
</filter>
<filter-mapping>
    <filter-name>gzipResponseFilter</filter-name>
    <servlet-name>facesServlet</servlet-name>
    <dispatcher>REQUEST</dispatcher>
    <dispatcher>ERROR</dispatcher>
</filter-mapping>

Configuration (optional)

This filter supports two initialization parameters which needs to be placed in <filter> element as follows:

<init-param>
    <description>The threshold size in bytes. Must be a number between 0 and 9999. Defaults to 150.</description>
    <param-name>threshold</param-name>
    <param-value>150</param-value>
</init-param>
<init-param>
    <description>The mimetypes which needs to be compressed. Must be a commaseparated string. Defaults to the below values.</description>
    <param-name>mimetypes</param-name>
    <param-value>
        text/plain, text/html, text/xml, text/css, text/javascript, text/csv, text/rtf,
        application/xml, application/xhtml+xml, application/javascript, application/x-javascript, application/json,
        image/svg+xml
    </param-value>
</init-param>

The default threshold is thus 150 bytes. This means that when the response is not larger than 150 bytes, then it will not be compressed with GZIP. Only when it's larger than 150 bytes, then it will be compressed. A threshold of between 150 and 1000 bytes is recommended due to overhead and latency of compression/decompression. The value must be a number between 0 and 9999. A value larger than 2000 is not recommended.

The mimetypes represents a comma separated string of mime types which needs to be compressed. It's exactly that value which appears in the Content-Type header of the response. The in the above example mentioned mime types are already the default values. Note that GZIP does not have any benefit when applied on binary mimetypes like images, office documents, PDF files, etcetera. So setting it for them is not recommended.

Since 3.11, application/x-javascript has been added to default mimetypes.