Resin Documentation

filters

Filter configuration follows the Servlet 3.0 deployment descriptors. Creating and using a filter has three steps:

1. Create a filter class which extends javax.servlet.Filter
2. Use <filter> in the web.xml to configure the filter.
3. Use <filter-mapping> to select URLs and servlets for the filter.

<web-app id='/'>

<filter-mapping url-pattern='/images/*'
                 filter-name='image'/>

<filter filter-name='image'
         filter-class='test.MyImage'>
  <init-param title='Hello, World'/>
</filter>

</web-app>

<web-app id='/'>

<filter filter-name='test.HelloWorld'>
  <init-param foo='bar'/>

  <init-param>
    <param-name>baz</param-name>
    <param-value>value</param-value>
  </init-param>
</filter>

</web-app>

<caucho.com>
<web-app id='/'>

<servlet servlet-name='hello'
         servlet-class='test.HelloWorld'/>

<servlet-mapping url-pattern='/hello'
                 servlet-name='hello'/>

<filter filter-name='test-filter'
        filter-class='test.MyFilter'/>

<filter-mapping url-pattern='/hello/*'
                 filter-name='test-filter'/>

<filter-mapping servlet-name='hello'
                 filter-name='test.SecondFilter'/>

</web-app>

The GzipFilter compresses the output of pages for browsers which understand compression, and leaves the output unchanged if the browser does not support compression. A browser indicates to the server that it supports gzip compression by including "gzip" in the "Accept-Encoding" request header.

GzipFilter is available in Resin-Professional.

<web-app xmlns="http://caucho.com/ns/resin">
  <filter filter-name="gzip"
          filter-class="com.caucho.filters.GzipFilter"/>

  <filter-mapping url-pattern="/*" filter-name="gzip"/>
</web-app>

See com.caucho.filters.GzipFilter.

The XsltFilter transforms the response using xslt. A Servlet or a JSP can produce XML results which are transformed using xslt.

<web-app xmlns="http://caucho.com/ns/resin">
  <filter filter-name="xslt"
          filter-class="com.caucho.filters.XsltFilter"/>

  <filter-mapping url-pattern="/*.jsp" filter-name="xslt"/>
</web-app>

See com.caucho.servlets.XsltFilter.

<web-app xmlns="http://caucho.com/ns/resin">
  <class-loader>
    <simple-loader path="WEB-INF/xsl"/>
  </class-loader>

  ...
</web-app>


WEB-INF/xsl/default.xsl

<% request.setAttribute("caucho.xsl.stylesheet","transform.xsl"); %>

<?xml-stylesheet type="text/xsl" href="transform.xsl"?>

<web-app xmlns="http://caucho.com/ns/resin">
  <filter filter-name='xslt' filter-class='com.caucho.filters.XsltFilter'>
    <init>
      <unconditional>true</unconditional>
    </init>
  </filter>

  <filter-mapping url-pattern='/xslt/*' filter-name='xslt'/>
</web-app>

The TransactionFilter wraps the request in a UserTransaction and commits the transaction when the servlet completes. All database calls for the request will either succeed together or fail. The UserTransaction is obtained by doing a jndi lookup with the name "java:comp/UserTransaction".

This filter will gracefully handle any exceptions that occur during the request by doing a rollback on the transaction.

<web-app xmlns="http://caucho.com/ns/resin">
  <filter filter-name='transaction-filter'
          filter-class='com.caucho.filters.TransactionFilter'/>

  <filter-mapping url-pattern='/DatabaseServlet/*'
                  filter-name='transaction-filter'/>
</web-app>

See com.caucho.servlets.TransactionFilter.

The ExpiresFilter sets the Expires cache control header, allowing servlet output and jsp results to be cached for a short time.

This is useful for indicating an Expires time to the browser, and it is even more useful when used in conjunction with Resin's HTTP proxy cache. If Resin's HTTP proxy cache is in use, even a short Expires time (like 2s) can result in performance gains.

<web-app xmlns="http://caucho.com/ns/resin">
  <filter filter-name='expires-60s'
          filter-class='com.caucho.filters.ExpiresFilter'>
    <init>
      <cache-time>60s</cache-time>
    </init>
  </filter>

  <filter-mapping servlet-name='StockQuoteServlet'
                  filter-name='expires-60s'/>
</web-app>

In this example, the StockQuoteServlet will be only called once every 60 seconds. This indicates to a browser that it should refresh it's local cache of the url after 60 seconds have passed. If Resin's HTTP proxy cache is being used, the first request from any browser will cause execution of the StockQuoteServlet, any requests from any browser for the next 60 seconds will be served from the proxy cache (the servlet will not be called).

See com.caucho.servlets.ExpiresFilter.

The AnonymousExpiresFilter caches the response for anonymous users. A user is anonymous if the do not have a session. When a page has custom formatting for logged in users, it may still want to cache the results for non-logged in users saving time and database access.

The benefits of using this filter are similar to those described in ExpiresFilter.

Servlets should call request.getSession(false) to get their sessions, because once a session is created the response will no longer be cached. For the same reason, JSP pages should set <jsp:directive.page session='false'/> for all pages that do not need a session.

<web-app xmlns="http://caucho.com/ns/resin">
  <filter filter-name='anonymous-expires'
          filter-class='com.caucho.filters.AnonymousExpiresFilter'>
    <init>
      <cache-time>15m</cache-time>
    </init>
  </filter>

  <filter-mapping url-pattern='*.jsp'
                  filter-name='anonymous-expires'/>
</web-app>

See com.caucho.servlets.AnonymousExpiresFilter.

The RewriteFilter rewrites and forwards URLs matching a regular expression. It is useful either when URLs change during a site redesign or when a site might want to hide its JSP structure. The functionality is similar to mod_rewrite in the Apache web server.

The RewriteFilter is configured with a list of <rewrite> tags. Each tag has a pattern which matches against the URL and a target which specifies the new URL to be forwarded to. Multiple <rewrite> tags are allowed.

<filter filter-name='rewrite'
        filter-class='com.caucho.filters.RewriteFilter'>
  <init>
    <rewrite pattern="/a/([^/]*)/([^?]*)" target="/$2/$1.jsp"/>
    <rewrite pattern="/b/([^/]*)/([^?]*)" target="/$2/$1.html"/>
  </init>
</filter>

<filter-mapping url-pattern='/*' filter-name='rewrite'/>

See com.caucho.servlets.RewriteFilter.

The ThrottleFilter filter restricts the number of requests from the same IP, defaulting to 2 (the HTTP spec limit.) The ThrottleFilter is useful to limit some parallel download programs that can use more threads than they should.

<filter filter-name="throttle"
        filter-class="com.caucho.filters.ThrottleFilter">
  <init>
    <max-concurrent-requests>2</max-concurrent-requests>
  </init>
</filter>

<filter-mapping url-pattern="/*" filter-name="throttle"/>

See com.caucho.filters.ThrottleFilter.