Package org.openremote.container.web.file

Class GzipResponseFilter

java.lang.Object

org.openremote.container.web.file.HttpFilter

org.openremote.container.web.file.GzipResponseFilter

All Implemented Interfaces:

javax.servlet.Filter

public class GzipResponseFilter
extends HttpFilter

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 comma separated 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/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.

The zipped init parameter is a list of file name extensions which are considered already zipped, so only a gzip header must be added to the response for such files.

Since:

1.1

See Also:

• GzipHttpServletResponse
• HttpServletResponseOutputWrapper
• ResettableBuffer
• ResettableBufferedOutputStream
• ResettableBufferedWriter
• HttpFilter

Constructor Summary

Constructors

Constructor	Description
GzipResponseFilter()
GzipResponseFilter(String[] mimetypes)

Method Summary

Modifier and Type	Method	Description
void	doFilter(javax.servlet.http.HttpServletRequest request, javax.servlet.http.HttpServletResponse response, javax.servlet.http.HttpSession session, javax.servlet.FilterChain chain)	Perform the filtering job.
void	init()	Initializes the filter parameters.

Methods inherited from class org.openremote.container.web.file.HttpFilter

destroy, doFilter, getFilterConfig, getInitParameter, getServletContext, init

Methods inherited from class java.lang.Object

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

Constructor Details

GzipResponseFilter

public GzipResponseFilter()

GzipResponseFilter

public GzipResponseFilter(String[] mimetypes)

Method Details

init

public void init()
          throws javax.servlet.ServletException

Initializes the filter parameters.

Overrides:

init in class HttpFilter

Throws:

javax.servlet.ServletException - When filter's initialization failed.

doFilter

public void doFilter(javax.servlet.http.HttpServletRequest request,
 javax.servlet.http.HttpServletResponse response,
 javax.servlet.http.HttpSession session,
 javax.servlet.FilterChain chain)
              throws javax.servlet.ServletException,
IOException

Perform the filtering job. Only if the client accepts GZIP based on the request headers, then wrap the response in a GzipHttpServletResponse and pass it through the filter chain.

Specified by:

doFilter in class HttpFilter

Parameters:

request - The HTTP request.

response - The HTTP response.

session - The HTTP session, if any, else null.

chain - The filter chain to continue.

Throws:

javax.servlet.ServletException - As wrapper exception when something fails in the request processing.

IOException - Whenever something fails at I/O level.

See Also:

• Filter.doFilter(ServletRequest, ServletResponse, FilterChain)